#
cargo/core/
global_cache_tracker.rs

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    1815
    1816

    //! Support for tracking the last time files were used to assist with cleaning
    //! up those files if they haven't been used in a while.
    //!
    //! Tracking of cache files is stored in a sqlite database which contains a
    //! timestamp of the last time the file was used, as well as the size of the
    //! file.
    //!
    //! While cargo is running, when it detects a use of a cache file, it adds a
    //! timestamp to [`DeferredGlobalLastUse`]. This batches up a set of changes
    //! that are then flushed to the database all at once (via
    //! [`DeferredGlobalLastUse::save`]). Ideally saving would only be done once
    //! for performance reasons, but that is not really possible due to the way
    //! cargo works, since there are different ways cargo can be used (like `cargo
    //! generate-lockfile`, `cargo fetch`, and `cargo build` are all very
    //! different ways the code is used).
    //!
    //! All of the database interaction is done through the [`GlobalCacheTracker`]
    //! type.
    //!
    //! There is a single global [`GlobalCacheTracker`] and
    //! [`DeferredGlobalLastUse`] stored in [`GlobalContext`].
    //!
    //! The high-level interface for performing garbage collection is defined in
    //! the [`crate::core::gc`] module. The functions there are responsible for
    //! interacting with the [`GlobalCacheTracker`] to handle cleaning of global
    //! cache data.
    //!
    //! ## Automatic gc
    //!
    //! Some commands (primarily the build commands) will trigger an automatic
    //! deletion of files that haven't been used in a while. The high-level
    //! interface for this is the [`crate::core::gc::auto_gc`] function.
    //!
    //! The [`GlobalCacheTracker`] database tracks the last time an automatic gc
    //! was performed so that it is only done once per day for performance
    //! reasons.
    //!
    //! ## Manual gc
    //!
    //! The user can perform a manual garbage collection with the `cargo clean`
    //! command. That command has a variety of options to specify what to delete.
    //! Manual gc supports deleting based on age or size or both. From a
    //! high-level, this is done by the [`crate::core::gc::Gc::gc`] method, which
    //! calls into [`GlobalCacheTracker`] to handle all the cleaning.
    //!
    //! ## Locking
    //!
    //! Usage of the database requires that the package cache is locked to prevent
    //! concurrent access. Although sqlite has built-in locking support, we want
    //! to use cargo's locking so that the "Blocking" message gets displayed, and
    //! so that locks can block indefinitely for long-running build commands.
    //! [`rusqlite`] has a default timeout of 5 seconds, though that is
    //! configurable.
    //!
    //! When garbage collection is being performed, the package cache lock must be
    //! in [`CacheLockMode::MutateExclusive`] to ensure no other cargo process is
    //! running. See [`crate::util::cache_lock`] for more detail on locking.
    //!
    //! When performing automatic gc, [`crate::core::gc::auto_gc`] will skip the
    //! GC if the package cache lock is already held by anything else. Automatic
    //! GC is intended to be opportunistic, and should impose as little disruption
    //! to the user as possible.
    //!
    //! ## Compatibility
    //!
    //! The database must retain both forwards and backwards compatibility between
    //! different versions of cargo. For the most part, this shouldn't be too
    //! difficult to maintain. Generally sqlite doesn't change on-disk formats
    //! between versions (the introduction of WAL is one of the few examples where
    //! version 3 had a format change, but we wouldn't use it anyway since it has
    //! shared-memory requirements cargo can't depend on due to things like
    //! network mounts).
    //!
    //! Schema changes must be managed through [`migrations`] by adding new
    //! entries that make a change to the database. Changes must not break older
    //! versions of cargo. Generally, adding columns should be fine (either with a
    //! default value, or NULL). Adding tables should also be fine. Just don't do
    //! destructive things like removing a column, or changing the semantics of an
    //! existing column.
    //!
    //! Since users may run older versions of cargo that do not do cache tracking,
    //! the [`GlobalCacheTracker::sync_db_with_files`] method helps dealing with
    //! keeping the database in sync in the presence of older versions of cargo
    //! touching the cache directories.
    //!
    //! ## Performance
    //!
    //! A lot of focus on the design of this system is to minimize the performance
    //! impact. Every build command needs to save updates which we try to avoid
    //! having a noticeable impact on build times. Systems like Windows,
    //! particularly with a magnetic hard disk, can experience a fairly large
    //! impact of cargo's overhead. Cargo's benchsuite has some benchmarks to help
    //! compare different environments, or changes to the code here. Please try to
    //! keep performance in mind if making any major changes.
    //!
    //! Performance of `cargo clean` is not quite as important since it is not
    //! expected to be run often. However, it is still courteous to the user to
    //! try to not impact it too much. One part that has a performance concern is
    //! that the clean command will synchronize the database with whatever is on
    //! disk if needed (in case files were added by older versions of cargo that
    //! don't do cache tracking, or if the user manually deleted some files). This
    //! can potentially be very slow, especially if the two are very out of sync.
    //!
    //! ## Filesystems
    //!
    //! Everything here is sensitive to the kind of filesystem it is running on.
    //! People tend to run cargo in all sorts of strange environments that have
    //! limited capabilities, or on things like read-only mounts. The code here
    //! needs to gracefully handle as many situations as possible.
    //!
    //! See also the information in the [Performance](#performance) and
    //! [Locking](#locking) sections when considering different filesystems and
    //! their impact on performance and locking.
    //!
    //! There are checks for read-only filesystems, which is generally ignored.

    use crate::core::gc::GcOpts;
    use crate::core::Verbosity;
    use crate::ops::CleanContext;
    use crate::util::cache_lock::CacheLockMode;
    use crate::util::interning::InternedString;
    use crate::util::sqlite::{self, basic_migration, Migration};
    use crate::util::{Filesystem, Progress, ProgressStyle};
    use crate::{CargoResult, GlobalContext};
    use anyhow::{bail, Context as _};
    use cargo_util::paths;
    use rusqlite::{params, Connection, ErrorCode};
    use std::collections::{hash_map, HashMap};
    use std::path::{Path, PathBuf};
    use std::time::{Duration, SystemTime};
    use tracing::{debug, trace};

    /// The filename of the database.
    const GLOBAL_CACHE_FILENAME: &str = ".global-cache";

    const REGISTRY_INDEX_TABLE: &str = "registry_index";
    const REGISTRY_CRATE_TABLE: &str = "registry_crate";
    const REGISTRY_SRC_TABLE: &str = "registry_src";
    const GIT_DB_TABLE: &str = "git_db";
    const GIT_CO_TABLE: &str = "git_checkout";

    /// How often timestamps will be updated.
    ///
    /// As an optimization timestamps are not updated unless they are older than
    /// the given number of seconds. This helps reduce the amount of disk I/O when
    /// running cargo multiple times within a short window.
    const UPDATE_RESOLUTION: u64 = 60 * 5;

    /// Type for timestamps as stored in the database.
    ///
    /// These are seconds since the Unix epoch.
    type Timestamp = u64;

    /// The key for a registry index entry stored in the database.
    #[derive(Clone, Debug, Hash, Eq, PartialEq)]
    pub struct RegistryIndex {
        /// A unique name of the registry source.
        pub encoded_registry_name: InternedString,
    }

    /// The key for a registry `.crate` entry stored in the database.
    #[derive(Clone, Debug, Hash, Eq, PartialEq)]
    pub struct RegistryCrate {
        /// A unique name of the registry source.
        pub encoded_registry_name: InternedString,
        /// The filename of the compressed crate, like `foo-1.2.3.crate`.
        pub crate_filename: InternedString,
        /// The size of the `.crate` file.
        pub size: u64,
    }

    /// The key for a registry src directory entry stored in the database.
    #[derive(Clone, Debug, Hash, Eq, PartialEq)]
    pub struct RegistrySrc {
        /// A unique name of the registry source.
        pub encoded_registry_name: InternedString,
        /// The directory name of the extracted source, like `foo-1.2.3`.
        pub package_dir: InternedString,
        /// Total size of the src directory in bytes.
        ///
        /// This can be None when the size is unknown. For example, when the src
        /// directory already exists on disk, and we just want to update the
        /// last-use timestamp. We don't want to take the expense of computing disk
        /// usage unless necessary. [`GlobalCacheTracker::populate_untracked`]
        /// will handle any actual NULL values in the database, which can happen
        /// when the src directory is created by an older version of cargo that
        /// did not track sizes.
        pub size: Option<u64>,
    }

    /// The key for a git db entry stored in the database.
    #[derive(Clone, Debug, Hash, Eq, PartialEq)]
    pub struct GitDb {
        /// A unique name of the git database.
        pub encoded_git_name: InternedString,
    }

    /// The key for a git checkout entry stored in the database.
    #[derive(Clone, Debug, Hash, Eq, PartialEq)]
    pub struct GitCheckout {
        /// A unique name of the git database.
        pub encoded_git_name: InternedString,
        /// A unique name of the checkout without the database.
        pub short_name: InternedString,
        /// Total size of the checkout directory.
        ///
        /// This can be None when the size is unknown. See [`RegistrySrc::size`]
        /// for an explanation.
        pub size: Option<u64>,
    }

    /// Filesystem paths in the global cache.
    ///
    /// Accessing these assumes a lock has already been acquired.
    struct BasePaths {
        /// Root path to the index caches.
        index: PathBuf,
        /// Root path to the git DBs.
        git_db: PathBuf,
        /// Root path to the git checkouts.
        git_co: PathBuf,
        /// Root path to the `.crate` files.
        crate_dir: PathBuf,
        /// Root path to the `src` directories.
        src: PathBuf,
    }

    /// Migrations which initialize the database, and can be used to evolve it over time.
    ///
    /// See [`Migration`] for more detail.
    ///
    /// **Be sure to not change the order or entries here!**
    fn migrations() -> Vec<Migration> {
        vec![
            // registry_index tracks the overall usage of an index cache, and tracks a
            // numeric ID to refer to that index that is used in other tables.
            basic_migration(
                "CREATE TABLE registry_index (
                    id INTEGER PRIMARY KEY AUTOINCREMENT,
                    name TEXT UNIQUE NOT NULL,
                    timestamp INTEGER NOT NULL
                )",
            ),
            // .crate files
            basic_migration(
                "CREATE TABLE registry_crate (
                    registry_id INTEGER NOT NULL,
                    name TEXT NOT NULL,
                    size INTEGER NOT NULL,
                    timestamp INTEGER NOT NULL,
                    PRIMARY KEY (registry_id, name),
                    FOREIGN KEY (registry_id) REFERENCES registry_index (id) ON DELETE CASCADE
                 )",
            ),
            // Extracted src directories
            //
            // Note that `size` can be NULL. This will happen when marking a src
            // directory as used that was created by an older version of cargo
            // that didn't do size tracking.
            basic_migration(
                "CREATE TABLE registry_src (
                    registry_id INTEGER NOT NULL,
                    name TEXT NOT NULL,
                    size INTEGER,
                    timestamp INTEGER NOT NULL,
                    PRIMARY KEY (registry_id, name),
                    FOREIGN KEY (registry_id) REFERENCES registry_index (id) ON DELETE CASCADE
                 )",
            ),
            // Git db directories
            basic_migration(
                "CREATE TABLE git_db (
                    id INTEGER PRIMARY KEY AUTOINCREMENT,
                    name TEXT UNIQUE NOT NULL,
                    timestamp INTEGER NOT NULL
                 )",
            ),
            // Git checkout directories
            basic_migration(
                "CREATE TABLE git_checkout (
                    git_id INTEGER NOT NULL,
                    name TEXT UNIQUE NOT NULL,
                    size INTEGER,
                    timestamp INTEGER NOT NULL,
                    PRIMARY KEY (git_id, name),
                    FOREIGN KEY (git_id) REFERENCES git_db (id) ON DELETE CASCADE
                 )",
            ),
            // This is a general-purpose single-row table that can store arbitrary
            // data. Feel free to add columns (with ALTER TABLE) if necessary.
            basic_migration(
                "CREATE TABLE global_data (
                    last_auto_gc INTEGER NOT NULL
                )",
            ),
            // last_auto_gc tracks the last time auto-gc was run (so that it only
            // runs roughly once a day for performance reasons). Prime it with the
            // current time to establish a baseline.
            Box::new(|conn| {
                conn.execute(
                    "INSERT INTO global_data (last_auto_gc) VALUES (?1)",
                    [now()],
                )?;
                Ok(())
            }),
        ]
    }

    /// Type for SQL columns that refer to the primary key of their parent table.
    ///
    /// For example, `registry_crate.registry_id` refers to its parent `registry_index.id`.
    #[derive(Copy, Clone, Debug, PartialEq)]
    struct ParentId(i64);

    impl rusqlite::types::FromSql for ParentId {
        fn column_result(value: rusqlite::types::ValueRef<'_>) -> rusqlite::types::FromSqlResult<Self> {
            let i = i64::column_result(value)?;
            Ok(ParentId(i))
        }
    }

    impl rusqlite::types::ToSql for ParentId {
        fn to_sql(&self) -> rusqlite::Result<rusqlite::types::ToSqlOutput<'_>> {
            Ok(rusqlite::types::ToSqlOutput::from(self.0))
        }
    }

    /// Tracking for the global shared cache (registry files, etc.).
    ///
    /// This is the interface to the global cache database, used for tracking and
    /// cleaning. See the [`crate::core::global_cache_tracker`] module docs for
    /// details.
    #[derive(Debug)]
    pub struct GlobalCacheTracker {
        /// Connection to the SQLite database.
        conn: Connection,
        /// This is an optimization used to make sure cargo only checks if gc
        /// needs to run once per session. This starts as `false`, and then the
        /// first time it checks if automatic gc needs to run, it will be set to
        /// `true`.
        auto_gc_checked_this_session: bool,
    }

    impl GlobalCacheTracker {
        /// Creates a new [`GlobalCacheTracker`].
        ///
        /// The caller is responsible for locking the package cache with
        /// [`CacheLockMode::DownloadExclusive`] before calling this.
        pub fn new(gctx: &GlobalContext) -> CargoResult<GlobalCacheTracker> {
            let db_path = Self::db_path(gctx);
            // A package cache lock is required to ensure only one cargo is
            // accessing at the same time. If there is concurrent access, we
            // want to rely on cargo's own "Blocking" system (which can
            // provide user feedback) rather than blocking inside sqlite
            // (which by default has a short timeout).
            let db_path = gctx.assert_package_cache_locked(CacheLockMode::DownloadExclusive, &db_path);
            let mut conn = Connection::open(db_path)?;
            conn.pragma_update(None, "foreign_keys", true)?;
            sqlite::migrate(&mut conn, &migrations())?;
            Ok(GlobalCacheTracker {
                conn,
                auto_gc_checked_this_session: false,
            })
        }

        /// The path to the database.
        pub fn db_path(gctx: &GlobalContext) -> Filesystem {
            gctx.home().join(GLOBAL_CACHE_FILENAME)
        }

        /// Given an encoded registry name, returns its ID.
        ///
        /// Returns None if the given name isn't in the database.
        fn id_from_name(
            conn: &Connection,
            table_name: &str,
            encoded_name: &str,
        ) -> CargoResult<Option<ParentId>> {
            let mut stmt =
                conn.prepare_cached(&format!("SELECT id FROM {table_name} WHERE name = ?"))?;
            match stmt.query_row([encoded_name], |row| row.get(0)) {
                Ok(id) => Ok(Some(id)),
                Err(rusqlite::Error::QueryReturnedNoRows) => Ok(None),
                Err(e) => Err(e.into()),
            }
        }

        /// Returns a map of ID to path for the given ids in the given table.
        ///
        /// For example, given `registry_index` IDs, it returns filenames of the
        /// form "index.crates.io-6f17d22bba15001f".
        fn get_id_map(
            conn: &Connection,
            table_name: &str,
            ids: &[i64],
        ) -> CargoResult<HashMap<i64, PathBuf>> {
            let mut stmt =
                conn.prepare_cached(&format!("SELECT name FROM {table_name} WHERE id = ?1"))?;
            ids.iter()
                .map(|id| {
                    let name = stmt.query_row(params![id], |row| {
                        Ok(PathBuf::from(row.get::<_, String>(0)?))
                    })?;
                    Ok((*id, name))
                })
                .collect()
        }

        /// Returns all index cache timestamps.
        pub fn registry_index_all(&self) -> CargoResult<Vec<(RegistryIndex, Timestamp)>> {
            let mut stmt = self
                .conn
                .prepare_cached("SELECT name, timestamp FROM registry_index")?;
            let rows = stmt
                .query_map([], |row| {
                    let encoded_registry_name = row.get_unwrap(0);
                    let timestamp = row.get_unwrap(1);
                    let kind = RegistryIndex {
                        encoded_registry_name,
                    };
                    Ok((kind, timestamp))
                })?
                .collect::<Result<Vec<_>, _>>()?;
            Ok(rows)
        }

        /// Returns all registry crate cache timestamps.
        pub fn registry_crate_all(&self) -> CargoResult<Vec<(RegistryCrate, Timestamp)>> {
            let mut stmt = self.conn.prepare_cached(
                "SELECT registry_index.name, registry_crate.name, registry_crate.size, registry_crate.timestamp
                 FROM registry_index, registry_crate
                 WHERE registry_crate.registry_id = registry_index.id",
            )?;
            let rows = stmt
                .query_map([], |row| {
                    let encoded_registry_name = row.get_unwrap(0);
                    let crate_filename = row.get_unwrap(1);
                    let size = row.get_unwrap(2);
                    let timestamp = row.get_unwrap(3);
                    let kind = RegistryCrate {
                        encoded_registry_name,
                        crate_filename,
                        size,
                    };
                    Ok((kind, timestamp))
                })?
                .collect::<Result<Vec<_>, _>>()?;
            Ok(rows)
        }

        /// Returns all registry source cache timestamps.
        pub fn registry_src_all(&self) -> CargoResult<Vec<(RegistrySrc, Timestamp)>> {
            let mut stmt = self.conn.prepare_cached(
                "SELECT registry_index.name, registry_src.name, registry_src.size, registry_src.timestamp
                 FROM registry_index, registry_src
                 WHERE registry_src.registry_id = registry_index.id",
            )?;
            let rows = stmt
                .query_map([], |row| {
                    let encoded_registry_name = row.get_unwrap(0);
                    let package_dir = row.get_unwrap(1);
                    let size = row.get_unwrap(2);
                    let timestamp = row.get_unwrap(3);
                    let kind = RegistrySrc {
                        encoded_registry_name,
                        package_dir,
                        size,
                    };
                    Ok((kind, timestamp))
                })?
                .collect::<Result<Vec<_>, _>>()?;
            Ok(rows)
        }

        /// Returns all git db timestamps.
        pub fn git_db_all(&self) -> CargoResult<Vec<(GitDb, Timestamp)>> {
            let mut stmt = self
                .conn
                .prepare_cached("SELECT name, timestamp FROM git_db")?;
            let rows = stmt
                .query_map([], |row| {
                    let encoded_git_name = row.get_unwrap(0);
                    let timestamp = row.get_unwrap(1);
                    let kind = GitDb { encoded_git_name };
                    Ok((kind, timestamp))
                })?
                .collect::<Result<Vec<_>, _>>()?;
            Ok(rows)
        }

        /// Returns all git checkout timestamps.
        pub fn git_checkout_all(&self) -> CargoResult<Vec<(GitCheckout, Timestamp)>> {
            let mut stmt = self.conn.prepare_cached(
                "SELECT git_db.name, git_checkout.name, git_checkout.size, git_checkout.timestamp
                 FROM git_db, git_checkout
                 WHERE git_checkout.git_id = git_db.id",
            )?;
            let rows = stmt
                .query_map([], |row| {
                    let encoded_git_name = row.get_unwrap(0);
                    let short_name = row.get_unwrap(1);
                    let size = row.get_unwrap(2);
                    let timestamp = row.get_unwrap(3);
                    let kind = GitCheckout {
                        encoded_git_name,
                        short_name,
                        size,
                    };
                    Ok((kind, timestamp))
                })?
                .collect::<Result<Vec<_>, _>>()?;
            Ok(rows)
        }

        /// Returns whether or not an auto GC should be performed, compared to the
        /// last time it was recorded in the database.
        pub fn should_run_auto_gc(&mut self, frequency: Duration) -> CargoResult<bool> {
            trace!(target: "gc", "should_run_auto_gc");
            if self.auto_gc_checked_this_session {
                return Ok(false);
            }
            let last_auto_gc: Timestamp =
                self.conn
                    .query_row("SELECT last_auto_gc FROM global_data", [], |row| row.get(0))?;
            let should_run = last_auto_gc + frequency.as_secs() < now();
            trace!(target: "gc",
                "last auto gc was {}, {}",
                last_auto_gc,
                if should_run { "running" } else { "skipping" }
            );
            self.auto_gc_checked_this_session = true;
            Ok(should_run)
        }

        /// Writes to the database to indicate that an automatic GC has just been
        /// completed.
        pub fn set_last_auto_gc(&self) -> CargoResult<()> {
            self.conn
                .execute("UPDATE global_data SET last_auto_gc = ?1", [now()])?;
            Ok(())
        }

        /// Deletes files from the global cache based on the given options.
        pub fn clean(&mut self, clean_ctx: &mut CleanContext<'_>, gc_opts: &GcOpts) -> CargoResult<()> {
            self.clean_inner(clean_ctx, gc_opts)
                .context("failed to clean entries from the global cache")
        }

        #[tracing::instrument(skip_all)]
        fn clean_inner(
            &mut self,
            clean_ctx: &mut CleanContext<'_>,
            gc_opts: &GcOpts,
        ) -> CargoResult<()> {
            let gctx = clean_ctx.gctx;
            let base = BasePaths {
                index: gctx.registry_index_path().into_path_unlocked(),
                git_db: gctx.git_db_path().into_path_unlocked(),
                git_co: gctx.git_checkouts_path().into_path_unlocked(),
                crate_dir: gctx.registry_cache_path().into_path_unlocked(),
                src: gctx.registry_source_path().into_path_unlocked(),
            };
            let now = now();
            trace!(target: "gc", "cleaning {gc_opts:?}");
            let tx = self.conn.transaction()?;
            let mut delete_paths = Vec::new();
            // This can be an expensive operation, so only perform it if necessary.
            if gc_opts.is_download_cache_opt_set() {
                // TODO: Investigate how slow this might be.
                Self::sync_db_with_files(
                    &tx,
                    now,
                    gctx,
                    &base,
                    gc_opts.is_download_cache_size_set(),
                    &mut delete_paths,
                )
                .context("failed to sync tracking database")?
            }
            if let Some(max_age) = gc_opts.max_index_age {
                let max_age = now - max_age.as_secs();
                Self::get_registry_index_to_clean(&tx, max_age, &base, &mut delete_paths)?;
            }
            if let Some(max_age) = gc_opts.max_src_age {
                let max_age = now - max_age.as_secs();
                Self::get_registry_items_to_clean_age(
                    &tx,
                    max_age,
                    REGISTRY_SRC_TABLE,
                    &base.src,
                    &mut delete_paths,
                )?;
            }
            if let Some(max_age) = gc_opts.max_crate_age {
                let max_age = now - max_age.as_secs();
                Self::get_registry_items_to_clean_age(
                    &tx,
                    max_age,
                    REGISTRY_CRATE_TABLE,
                    &base.crate_dir,
                    &mut delete_paths,
                )?;
            }
            if let Some(max_age) = gc_opts.max_git_db_age {
                let max_age = now - max_age.as_secs();
                Self::get_git_db_items_to_clean(&tx, max_age, &base, &mut delete_paths)?;
            }
            if let Some(max_age) = gc_opts.max_git_co_age {
                let max_age = now - max_age.as_secs();
                Self::get_git_co_items_to_clean(&tx, max_age, &base.git_co, &mut delete_paths)?;
            }
            // Size collection must happen after date collection so that dates
            // have precedence, since size constraints are a more blunt
            // instrument.
            //
            // These are also complicated by the `--max-download-size` option
            // overlapping with `--max-crate-size` and `--max-src-size`, which
            // requires some coordination between those options which isn't
            // necessary with the age-based options. An item's age is either older
            // or it isn't, but contrast that with size which is based on the sum
            // of all tracked items. Also, `--max-download-size` is summed against
            // both the crate and src tracking, which requires combining them to
            // compute the size, and then separating them to calculate the correct
            // paths.
            if let Some(max_size) = gc_opts.max_crate_size {
                Self::get_registry_items_to_clean_size(
                    &tx,
                    max_size,
                    REGISTRY_CRATE_TABLE,
                    &base.crate_dir,
                    &mut delete_paths,
                )?;
            }
            if let Some(max_size) = gc_opts.max_src_size {
                Self::get_registry_items_to_clean_size(
                    &tx,
                    max_size,
                    REGISTRY_SRC_TABLE,
                    &base.src,
                    &mut delete_paths,
                )?;
            }
            if let Some(max_size) = gc_opts.max_git_size {
                Self::get_git_items_to_clean_size(&tx, max_size, &base, &mut delete_paths)?;
            }
            if let Some(max_size) = gc_opts.max_download_size {
                Self::get_registry_items_to_clean_size_both(&tx, max_size, &base, &mut delete_paths)?;
            }

            clean_ctx.remove_paths(&delete_paths)?;

            if clean_ctx.dry_run {
                tx.rollback()?;
            } else {
                tx.commit()?;
            }
            Ok(())
        }

        /// Returns a list of directory entries in the given path.
        fn names_from(path: &Path) -> CargoResult<Vec<String>> {
            let entries = match path.read_dir() {
                Ok(e) => e,
                Err(e) => {
                    if e.kind() == std::io::ErrorKind::NotFound {
                        return Ok(Vec::new());
                    } else {
                        return Err(
                            anyhow::Error::new(e).context(format!("failed to read path `{path:?}`"))
                        );
                    }
                }
            };
            let names = entries
                .filter_map(|entry| entry.ok()?.file_name().into_string().ok())
                .collect();
            Ok(names)
        }

        /// Synchronizes the database to match the files on disk.
        ///
        /// This performs the following cleanups:
        ///
        /// 1. Remove entries from the database that are missing on disk.
        /// 2. Adds missing entries to the database that are on disk (such as when
        ///    files are added by older versions of cargo).
        /// 3. Fills in the `size` column where it is NULL (such as when something
        ///    is added to disk by an older version of cargo, and one of the mark
        ///    functions marked it without knowing the size).
        ///
        ///    Size computations are only done if `sync_size` is set since it can
        ///    be a very expensive operation. This should only be set if the user
        ///    requested to clean based on the cache size.
        /// 4. Checks for orphaned files. For example, if there are `.crate` files
        ///    associated with an index that does not exist.
        ///
        ///    These orphaned files will be added to `delete_paths` so that the
        ///    caller can delete them.
        #[tracing::instrument(skip(conn, gctx, base, delete_paths))]
        fn sync_db_with_files(
            conn: &Connection,
            now: Timestamp,
            gctx: &GlobalContext,
            base: &BasePaths,
            sync_size: bool,
            delete_paths: &mut Vec<PathBuf>,
        ) -> CargoResult<()> {
            debug!(target: "gc", "starting db sync");
            // For registry_index and git_db, add anything that is missing in the db.
            Self::update_parent_for_missing_from_db(conn, now, REGISTRY_INDEX_TABLE, &base.index)?;
            Self::update_parent_for_missing_from_db(conn, now, GIT_DB_TABLE, &base.git_db)?;

            // For registry_crate, registry_src, and git_checkout, remove anything
            // from the db that isn't on disk.
            Self::update_db_for_removed(
                conn,
                REGISTRY_INDEX_TABLE,
                "registry_id",
                REGISTRY_CRATE_TABLE,
                &base.crate_dir,
            )?;
            Self::update_db_for_removed(
                conn,
                REGISTRY_INDEX_TABLE,
                "registry_id",
                REGISTRY_SRC_TABLE,
                &base.src,
            )?;
            Self::update_db_for_removed(conn, GIT_DB_TABLE, "git_id", GIT_CO_TABLE, &base.git_co)?;

            // For registry_index and git_db, remove anything from the db that
            // isn't on disk.
            //
            // This also collects paths for any child files that don't have their
            // respective parent on disk.
            Self::update_db_parent_for_removed_from_disk(
                conn,
                REGISTRY_INDEX_TABLE,
                &base.index,
                &[&base.crate_dir, &base.src],
                delete_paths,
            )?;
            Self::update_db_parent_for_removed_from_disk(
                conn,
                GIT_DB_TABLE,
                &base.git_db,
                &[&base.git_co],
                delete_paths,
            )?;

            // For registry_crate, registry_src, and git_checkout, add anything
            // that is missing in the db.
            Self::populate_untracked_crate(conn, now, &base.crate_dir)?;
            Self::populate_untracked(
                conn,
                now,
                gctx,
                REGISTRY_INDEX_TABLE,
                "registry_id",
                REGISTRY_SRC_TABLE,
                &base.src,
                sync_size,
            )?;
            Self::populate_untracked(
                conn,
                now,
                gctx,
                GIT_DB_TABLE,
                "git_id",
                GIT_CO_TABLE,
                &base.git_co,
                sync_size,
            )?;

            // Update any NULL sizes if needed.
            if sync_size {
                Self::update_null_sizes(
                    conn,
                    gctx,
                    REGISTRY_INDEX_TABLE,
                    "registry_id",
                    REGISTRY_SRC_TABLE,
                    &base.src,
                )?;
                Self::update_null_sizes(
                    conn,
                    gctx,
                    GIT_DB_TABLE,
                    "git_id",
                    GIT_CO_TABLE,
                    &base.git_co,
                )?;
            }
            Ok(())
        }

        /// For parent tables, add any entries that are on disk but aren't tracked in the db.
        #[tracing::instrument(skip(conn, now, base_path))]
        fn update_parent_for_missing_from_db(
            conn: &Connection,
            now: Timestamp,
            parent_table_name: &str,
            base_path: &Path,
        ) -> CargoResult<()> {
            trace!(target: "gc", "checking for untracked parent to add to {parent_table_name}");
            let names = Self::names_from(base_path)?;

            let mut stmt = conn.prepare_cached(&format!(
                "INSERT INTO {parent_table_name} (name, timestamp)
                    VALUES (?1, ?2)
                    ON CONFLICT DO NOTHING",
            ))?;
            for name in names {
                stmt.execute(params![name, now])?;
            }
            Ok(())
        }

        /// Removes database entries for any files that are not on disk for the child tables.
        ///
        /// This could happen for example if the user manually deleted the file or
        /// any such scenario where the filesystem and db are out of sync.
        #[tracing::instrument(skip(conn, base_path))]
        fn update_db_for_removed(
            conn: &Connection,
            parent_table_name: &str,
            id_column_name: &str,
            table_name: &str,
            base_path: &Path,
        ) -> CargoResult<()> {
            trace!(target: "gc", "checking for db entries to remove from {table_name}");
            let mut select_stmt = conn.prepare_cached(&format!(
                "SELECT {table_name}.rowid, {parent_table_name}.name, {table_name}.name
                 FROM {parent_table_name}, {table_name}
                 WHERE {table_name}.{id_column_name} = {parent_table_name}.id",
            ))?;
            let mut delete_stmt =
                conn.prepare_cached(&format!("DELETE FROM {table_name} WHERE rowid = ?1"))?;
            let mut rows = select_stmt.query([])?;
            while let Some(row) = rows.next()? {
                let rowid: i64 = row.get_unwrap(0);
                let id_name: String = row.get_unwrap(1);
                let name: String = row.get_unwrap(2);
                if !base_path.join(id_name).join(name).exists() {
                    delete_stmt.execute([rowid])?;
                }
            }
            Ok(())
        }

        /// Removes database entries for any files that are not on disk for the parent tables.
        #[tracing::instrument(skip(conn, base_path, child_base_paths, delete_paths))]
        fn update_db_parent_for_removed_from_disk(
            conn: &Connection,
            parent_table_name: &str,
            base_path: &Path,
            child_base_paths: &[&Path],
            delete_paths: &mut Vec<PathBuf>,
        ) -> CargoResult<()> {
            trace!(target: "gc", "checking for db entries to remove from {parent_table_name}");
            let mut select_stmt =
                conn.prepare_cached(&format!("SELECT rowid, name FROM {parent_table_name}"))?;
            let mut delete_stmt =
                conn.prepare_cached(&format!("DELETE FROM {parent_table_name} WHERE rowid = ?1"))?;
            let mut rows = select_stmt.query([])?;
            while let Some(row) = rows.next()? {
                let rowid: i64 = row.get_unwrap(0);
                let id_name: String = row.get_unwrap(1);
                if !base_path.join(&id_name).exists() {
                    delete_stmt.execute([rowid])?;
                    // Make sure any child data is also cleaned up.
                    for child_base in child_base_paths {
                        let child_path = child_base.join(&id_name);
                        if child_path.exists() {
                            debug!(target: "gc", "removing orphaned path {child_path:?}");
                            delete_paths.push(child_path);
                        }
                    }
                }
            }
            Ok(())
        }

        /// Updates the database to add any `.crate` files that are currently
        /// not tracked (such as when they are downloaded by an older version of
        /// cargo).
        #[tracing::instrument(skip(conn, now, base_path))]
        fn populate_untracked_crate(
            conn: &Connection,
            now: Timestamp,
            base_path: &Path,
        ) -> CargoResult<()> {
            trace!(target: "gc", "populating untracked crate files");
            let mut insert_stmt = conn.prepare_cached(
                "INSERT INTO registry_crate (registry_id, name, size, timestamp)
                 VALUES (?1, ?2, ?3, ?4)
                 ON CONFLICT DO NOTHING",
            )?;
            let index_names = Self::names_from(&base_path)?;
            for index_name in index_names {
                let Some(id) = Self::id_from_name(conn, REGISTRY_INDEX_TABLE, &index_name)? else {
                    // The id is missing from the database. This should be resolved
                    // via update_db_parent_for_removed_from_disk.
                    continue;
                };
                let index_path = base_path.join(index_name);
                for crate_name in Self::names_from(&index_path)? {
                    if crate_name.ends_with(".crate") {
                        // Missing files should have already been taken care of by
                        // update_db_for_removed.
                        let size = paths::metadata(index_path.join(&crate_name))?.len();
                        insert_stmt.execute(params![id, crate_name, size, now])?;
                    }
                }
            }
            Ok(())
        }

        /// Updates the database to add any files that are currently not tracked
        /// (such as when they are downloaded by an older version of cargo).
        #[tracing::instrument(skip(conn, now, gctx, base_path, populate_size))]
        fn populate_untracked(
            conn: &Connection,
            now: Timestamp,
            gctx: &GlobalContext,
            id_table_name: &str,
            id_column_name: &str,
            table_name: &str,
            base_path: &Path,
            populate_size: bool,
        ) -> CargoResult<()> {
            trace!(target: "gc", "populating untracked files for {table_name}");
            // Gather names (and make sure they are in the database).
            let id_names = Self::names_from(&base_path)?;

            // This SELECT is used to determine if the directory is already
            // tracked. We don't want to do the expensive size computation unless
            // necessary.
            let mut select_stmt = conn.prepare_cached(&format!(
                "SELECT 1 FROM {table_name}
                 WHERE {id_column_name} = ?1 AND name = ?2",
            ))?;
            let mut insert_stmt = conn.prepare_cached(&format!(
                "INSERT INTO {table_name} ({id_column_name}, name, size, timestamp)
                 VALUES (?1, ?2, ?3, ?4)
                 ON CONFLICT DO NOTHING",
            ))?;
            let mut progress = Progress::with_style("Scanning", ProgressStyle::Ratio, gctx);
            // Compute the size of any directory not in the database.
            for id_name in id_names {
                let Some(id) = Self::id_from_name(conn, id_table_name, &id_name)? else {
                    // The id is missing from the database. This should be resolved
                    // via update_db_parent_for_removed_from_disk.
                    continue;
                };
                let index_path = base_path.join(id_name);
                let names = Self::names_from(&index_path)?;
                let max = names.len();
                for (i, name) in names.iter().enumerate() {
                    if select_stmt.exists(params![id, name])? {
                        continue;
                    }
                    let dir_path = index_path.join(name);
                    if !dir_path.is_dir() {
                        continue;
                    }
                    progress.tick(i, max, "")?;
                    let size = if populate_size {
                        Some(du(&dir_path, table_name)?)
                    } else {
                        None
                    };
                    insert_stmt.execute(params![id, name, size, now])?;
                }
            }
            Ok(())
        }

        /// Fills in the `size` column where it is NULL.
        ///
        /// This can happen when something is added to disk by an older version of
        /// cargo, and one of the mark functions marked it without knowing the
        /// size.
        ///
        /// `update_db_for_removed` should be called before this is called.
        #[tracing::instrument(skip(conn, gctx, base_path))]
        fn update_null_sizes(
            conn: &Connection,
            gctx: &GlobalContext,
            parent_table_name: &str,
            id_column_name: &str,
            table_name: &str,
            base_path: &Path,
        ) -> CargoResult<()> {
            trace!(target: "gc", "updating NULL size information in {table_name}");
            let mut null_stmt = conn.prepare_cached(&format!(
                "SELECT {table_name}.rowid, {table_name}.name, {parent_table_name}.name
                 FROM {table_name}, {parent_table_name}
                 WHERE {table_name}.size IS NULL AND {table_name}.{id_column_name} = {parent_table_name}.id",
            ))?;
            let mut update_stmt = conn.prepare_cached(&format!(
                "UPDATE {table_name} SET size = ?1 WHERE rowid = ?2"
            ))?;
            let mut progress = Progress::with_style("Scanning", ProgressStyle::Ratio, gctx);
            let rows: Vec<_> = null_stmt
                .query_map([], |row| {
                    Ok((row.get_unwrap(0), row.get_unwrap(1), row.get_unwrap(2)))
                })?
                .collect();
            let max = rows.len();
            for (i, row) in rows.into_iter().enumerate() {
                let (rowid, name, id_name): (i64, String, String) = row?;
                let path = base_path.join(id_name).join(name);
                progress.tick(i, max, "")?;
                // Missing files should have already been taken care of by
                // update_db_for_removed.
                let size = du(&path, table_name)?;
                update_stmt.execute(params![size, rowid])?;
            }
            Ok(())
        }

        /// Adds paths to delete from either registry_crate or registry_src whose
        /// last use is older than the given timestamp.
        fn get_registry_items_to_clean_age(
            conn: &Connection,
            max_age: Timestamp,
            table_name: &str,
            base_path: &Path,
            delete_paths: &mut Vec<PathBuf>,
        ) -> CargoResult<()> {
            debug!(target: "gc", "cleaning {table_name} since {max_age:?}");
            let mut stmt = conn.prepare_cached(&format!(
                "DELETE FROM {table_name} WHERE timestamp < ?1
                    RETURNING registry_id, name"
            ))?;
            let rows = stmt
                .query_map(params![max_age], |row| {
                    let registry_id = row.get_unwrap(0);
                    let name: String = row.get_unwrap(1);
                    Ok((registry_id, name))
                })?
                .collect::<Result<Vec<_>, _>>()?;
            let ids: Vec<_> = rows.iter().map(|r| r.0).collect();
            let id_map = Self::get_id_map(conn, REGISTRY_INDEX_TABLE, &ids)?;
            for (id, name) in rows {
                let encoded_registry_name = &id_map[&id];
                delete_paths.push(base_path.join(encoded_registry_name).join(name));
            }
            Ok(())
        }

        /// Adds paths to delete from either `registry_crate` or `registry_src` in
        /// order to keep the total size under the given max size.
        fn get_registry_items_to_clean_size(
            conn: &Connection,
            max_size: u64,
            table_name: &str,
            base_path: &Path,
            delete_paths: &mut Vec<PathBuf>,
        ) -> CargoResult<()> {
            debug!(target: "gc", "cleaning {table_name} till under {max_size:?}");
            let total_size: u64 = conn.query_row(
                &format!("SELECT coalesce(SUM(size), 0) FROM {table_name}"),
                [],
                |row| row.get(0),
            )?;
            if total_size <= max_size {
                return Ok(());
            }
            // This SQL statement selects all of the rows ordered by timestamp,
            // and then uses a window function to keep a running total of the
            // size. It selects all rows until the running total exceeds the
            // threshold of the total number of bytes that we want to delete.
            //
            // The window function essentially computes an aggregate over all
            // previous rows as it goes along. As long as the running size is
            // below the total amount that we need to delete, it keeps picking
            // more rows.
            //
            // The ORDER BY includes `name` mainly for test purposes so that
            // entries with the same timestamp have deterministic behavior.
            //
            // The coalesce helps convert NULL to 0.
            let mut stmt = conn.prepare(&format!(
                "DELETE FROM {table_name} WHERE rowid IN \
                    (SELECT x.rowid FROM \
                        (SELECT rowid, size, SUM(size) OVER \
                            (ORDER BY timestamp, name ROWS UNBOUNDED PRECEDING) AS running_amount \
                            FROM {table_name}) x \
                        WHERE coalesce(x.running_amount, 0) - x.size < ?1) \
                    RETURNING registry_id, name;"
            ))?;
            let rows = stmt
                .query_map(params![total_size - max_size], |row| {
                    let id = row.get_unwrap(0);
                    let name: String = row.get_unwrap(1);
                    Ok((id, name))
                })?
                .collect::<Result<Vec<_>, _>>()?;
            // Convert registry_id to the encoded registry name, and join those.
            let ids: Vec<_> = rows.iter().map(|r| r.0).collect();
            let id_map = Self::get_id_map(conn, REGISTRY_INDEX_TABLE, &ids)?;
            for (id, name) in rows {
                let encoded_name = &id_map[&id];
                delete_paths.push(base_path.join(encoded_name).join(name));
            }
            Ok(())
        }

        /// Adds paths to delete from both `registry_crate` and `registry_src` in
        /// order to keep the total size under the given max size.
        fn get_registry_items_to_clean_size_both(
            conn: &Connection,
            max_size: u64,
            base: &BasePaths,
            delete_paths: &mut Vec<PathBuf>,
        ) -> CargoResult<()> {
            debug!(target: "gc", "cleaning download till under {max_size:?}");

            // This SQL statement selects from both registry_src and
            // registry_crate so that sorting of timestamps incorporates both of
            // them at the same time. It uses a const value of 1 or 2 as the first
            // column so that the code below can determine which table the value
            // came from.
            let mut stmt = conn.prepare_cached(
                "SELECT 1, registry_src.rowid, registry_src.name AS name, registry_index.name,
                        registry_src.size, registry_src.timestamp AS timestamp
                 FROM registry_src, registry_index
                 WHERE registry_src.registry_id = registry_index.id AND registry_src.size NOT NULL

                 UNION

                 SELECT 2, registry_crate.rowid, registry_crate.name AS name, registry_index.name,
                        registry_crate.size, registry_crate.timestamp AS timestamp
                 FROM registry_crate, registry_index
                 WHERE registry_crate.registry_id = registry_index.id

                 ORDER BY timestamp, name",
            )?;
            let mut delete_src_stmt =
                conn.prepare_cached("DELETE FROM registry_src WHERE rowid = ?1")?;
            let mut delete_crate_stmt =
                conn.prepare_cached("DELETE FROM registry_crate WHERE rowid = ?1")?;
            let rows = stmt
                .query_map([], |row| {
                    Ok((
                        row.get_unwrap(0),
                        row.get_unwrap(1),
                        row.get_unwrap(2),
                        row.get_unwrap(3),
                        row.get_unwrap(4),
                    ))
                })?
                .collect::<Result<Vec<(i64, i64, String, String, u64)>, _>>()?;
            let mut total_size: u64 = rows.iter().map(|r| r.4).sum();
            debug!(target: "gc", "total download cache size appears to be {total_size}");
            for (table, rowid, name, index_name, size) in rows {
                if total_size <= max_size {
                    break;
                }
                if table == 1 {
                    delete_paths.push(base.src.join(index_name).join(name));
                    delete_src_stmt.execute([rowid])?;
                } else {
                    delete_paths.push(base.crate_dir.join(index_name).join(name));
                    delete_crate_stmt.execute([rowid])?;
                }
                // TODO: If delete crate, ensure src is also deleted.
                total_size -= size;
            }
            Ok(())
        }

        /// Adds paths to delete from the git cache, keeping the total size under
        /// the give value.
        ///
        /// Paths are relative to the `git` directory in the cache directory.
        fn get_git_items_to_clean_size(
            conn: &Connection,
            max_size: u64,
            base: &BasePaths,
            delete_paths: &mut Vec<PathBuf>,
        ) -> CargoResult<()> {
            debug!(target: "gc", "cleaning git till under {max_size:?}");

            // Collect all the sizes from git_db and git_checkouts, and then sort them by timestamp.
            let mut stmt = conn.prepare_cached("SELECT rowid, name, timestamp FROM git_db")?;
            let mut git_info = stmt
                .query_map([], |row| {
                    let rowid: i64 = row.get_unwrap(0);
                    let name: String = row.get_unwrap(1);
                    let timestamp: Timestamp = row.get_unwrap(2);
                    // Size is added below so that the error doesn't need to be
                    // converted to a rusqlite error.
                    Ok((timestamp, rowid, None, name, 0))
                })?
                .collect::<Result<Vec<_>, _>>()?;
            for info in &mut git_info {
                let size = cargo_util::du(&base.git_db.join(&info.3), &[])?;
                info.4 = size;
            }

            let mut stmt = conn.prepare_cached(
                "SELECT git_checkout.rowid, git_db.name, git_checkout.name,
                    git_checkout.size, git_checkout.timestamp
                    FROM git_checkout, git_db
                    WHERE git_checkout.git_id = git_db.id AND git_checkout.size NOT NULL",
            )?;
            let git_co_rows = stmt
                .query_map([], |row| {
                    let rowid = row.get_unwrap(0);
                    let db_name: String = row.get_unwrap(1);
                    let name = row.get_unwrap(2);
                    let size = row.get_unwrap(3);
                    let timestamp = row.get_unwrap(4);
                    Ok((timestamp, rowid, Some(db_name), name, size))
                })?
                .collect::<Result<Vec<_>, _>>()?;
            git_info.extend(git_co_rows);

            // Sort by timestamp, and name. The name is included mostly for test
            // purposes so that entries with the same timestamp have deterministic
            // behavior.
            git_info.sort_by(|a, b| (b.0, &b.3).cmp(&(a.0, &a.3)));

            // Collect paths to delete.
            let mut delete_db_stmt = conn.prepare_cached("DELETE FROM git_db WHERE rowid = ?1")?;
            let mut delete_co_stmt =
                conn.prepare_cached("DELETE FROM git_checkout WHERE rowid = ?1")?;
            let mut total_size: u64 = git_info.iter().map(|r| r.4).sum();
            debug!(target: "gc", "total git cache size appears to be {total_size}");
            while let Some((_timestamp, rowid, db_name, name, size)) = git_info.pop() {
                if total_size <= max_size {
                    break;
                }
                if let Some(db_name) = db_name {
                    delete_paths.push(base.git_co.join(db_name).join(name));
                    delete_co_stmt.execute([rowid])?;
                    total_size -= size;
                } else {
                    total_size -= size;
                    delete_paths.push(base.git_db.join(&name));
                    delete_db_stmt.execute([rowid])?;
                    // If the db is deleted, then all the checkouts must be deleted.
                    let mut i = 0;
                    while i < git_info.len() {
                        if git_info[i].2.as_deref() == Some(name.as_ref()) {
                            let (_, rowid, db_name, name, size) = git_info.remove(i);
                            delete_paths.push(base.git_co.join(db_name.unwrap()).join(name));
                            delete_co_stmt.execute([rowid])?;
                            total_size -= size;
                        } else {
                            i += 1;
                        }
                    }
                }
            }
            Ok(())
        }

        /// Adds paths to delete from `registry_index` whose last use is older
        /// than the given timestamp.
        fn get_registry_index_to_clean(
            conn: &Connection,
            max_age: Timestamp,
            base: &BasePaths,
            delete_paths: &mut Vec<PathBuf>,
        ) -> CargoResult<()> {
            debug!(target: "gc", "cleaning index since {max_age:?}");
            let mut stmt = conn.prepare_cached(
                "DELETE FROM registry_index WHERE timestamp < ?1
                    RETURNING name",
            )?;
            let mut rows = stmt.query([max_age])?;
            while let Some(row) = rows.next()? {
                let name: String = row.get_unwrap(0);
                delete_paths.push(base.index.join(&name));
                // Also delete .crate and src directories, since by definition
                // they cannot be used without their index.
                delete_paths.push(base.src.join(&name));
                delete_paths.push(base.crate_dir.join(&name));
            }
            Ok(())
        }

        /// Adds paths to delete from `git_checkout` whose last use is
        /// older than the given timestamp.
        fn get_git_co_items_to_clean(
            conn: &Connection,
            max_age: Timestamp,
            base_path: &Path,
            delete_paths: &mut Vec<PathBuf>,
        ) -> CargoResult<()> {
            debug!(target: "gc", "cleaning git co since {max_age:?}");
            let mut stmt = conn.prepare_cached(
                "DELETE FROM git_checkout WHERE timestamp < ?1
                    RETURNING git_id, name",
            )?;
            let rows = stmt
                .query_map(params![max_age], |row| {
                    let git_id = row.get_unwrap(0);
                    let name: String = row.get_unwrap(1);
                    Ok((git_id, name))
                })?
                .collect::<Result<Vec<_>, _>>()?;
            let ids: Vec<_> = rows.iter().map(|r| r.0).collect();
            let id_map = Self::get_id_map(conn, GIT_DB_TABLE, &ids)?;
            for (id, name) in rows {
                let encoded_git_name = &id_map[&id];
                delete_paths.push(base_path.join(encoded_git_name).join(name));
            }
            Ok(())
        }

        /// Adds paths to delete from `git_db` in order to keep the total size
        /// under the given max size.
        fn get_git_db_items_to_clean(
            conn: &Connection,
            max_age: Timestamp,
            base: &BasePaths,
            delete_paths: &mut Vec<PathBuf>,
        ) -> CargoResult<()> {
            debug!(target: "gc", "cleaning git db since {max_age:?}");
            let mut stmt = conn.prepare_cached(
                "DELETE FROM git_db WHERE timestamp < ?1
                    RETURNING name",
            )?;
            let mut rows = stmt.query([max_age])?;
            while let Some(row) = rows.next()? {
                let name: String = row.get_unwrap(0);
                delete_paths.push(base.git_db.join(&name));
                // Also delete checkout directories, since by definition they
                // cannot be used without their db.
                delete_paths.push(base.git_co.join(&name));
            }
            Ok(())
        }
    }

    /// Helper to generate the upsert for the parent tables.
    ///
    /// This handles checking if the row already exists, and only updates the
    /// timestamp it if it hasn't been updated recently. This also handles keeping
    /// a cached map of the `id` value.
    ///
    /// Unfortunately it is a bit tricky to share this code without a macro.
    macro_rules! insert_or_update_parent {
        ($self:expr, $conn:expr, $table_name:expr, $timestamps_field:ident, $keys_field:ident, $encoded_name:ident) => {
            let mut select_stmt = $conn.prepare_cached(concat!(
                "SELECT id, timestamp FROM ",
                $table_name,
                " WHERE name = ?1"
            ))?;
            let mut insert_stmt = $conn.prepare_cached(concat!(
                "INSERT INTO ",
                $table_name,
                " (name, timestamp)
                    VALUES (?1, ?2)
                    ON CONFLICT DO UPDATE SET timestamp=excluded.timestamp
                    RETURNING id",
            ))?;
            let mut update_stmt = $conn.prepare_cached(concat!(
                "UPDATE ",
                $table_name,
                " SET timestamp = ?1 WHERE id = ?2"
            ))?;
            for (parent, new_timestamp) in std::mem::take(&mut $self.$timestamps_field) {
                trace!(target: "gc",
                    concat!("insert ", $table_name, " {:?} {}"),
                    parent,
                    new_timestamp
                );
                let mut rows = select_stmt.query([parent.$encoded_name])?;
                let id = if let Some(row) = rows.next()? {
                    let id: ParentId = row.get_unwrap(0);
                    let timestamp: Timestamp = row.get_unwrap(1);
                    if timestamp < new_timestamp - UPDATE_RESOLUTION {
                        update_stmt.execute(params![new_timestamp, id])?;
                    }
                    id
                } else {
                    insert_stmt.query_row(params![parent.$encoded_name, new_timestamp], |row| {
                        row.get(0)
                    })?
                };
                match $self.$keys_field.entry(parent.$encoded_name) {
                    hash_map::Entry::Occupied(o) => {
                        assert_eq!(*o.get(), id);
                    }
                    hash_map::Entry::Vacant(v) => {
                        v.insert(id);
                    }
                }
            }
            return Ok(());
        };
    }

    /// This is a cache of modifications that will be saved to disk all at once
    /// via the [`DeferredGlobalLastUse::save`] method.
    ///
    /// This is here to improve performance.
    #[derive(Debug)]
    pub struct DeferredGlobalLastUse {
        /// Cache of registry keys, used for faster fetching.
        ///
        /// The key is the registry name (which is its directory name) and the
        /// value is the `id` in the `registry_index` table.
        registry_keys: HashMap<InternedString, ParentId>,
        /// Cache of git keys, used for faster fetching.
        ///
        /// The key is the git db name (which is its directory name) and the value
        /// is the `id` in the `git_db` table.
        git_keys: HashMap<InternedString, ParentId>,

        /// New registry index entries to insert.
        registry_index_timestamps: HashMap<RegistryIndex, Timestamp>,
        /// New registry `.crate` entries to insert.
        registry_crate_timestamps: HashMap<RegistryCrate, Timestamp>,
        /// New registry src directory entries to insert.
        registry_src_timestamps: HashMap<RegistrySrc, Timestamp>,
        /// New git db entries to insert.
        git_db_timestamps: HashMap<GitDb, Timestamp>,
        /// New git checkout entries to insert.
        git_checkout_timestamps: HashMap<GitCheckout, Timestamp>,
        /// This is used so that a warning about failing to update the database is
        /// only displayed once.
        save_err_has_warned: bool,
        /// The current time, used to improve performance to avoid accessing the
        /// clock hundreds of times.
        now: Timestamp,
    }

    impl DeferredGlobalLastUse {
        pub fn new() -> DeferredGlobalLastUse {
            DeferredGlobalLastUse {
                registry_keys: HashMap::new(),
                git_keys: HashMap::new(),
                registry_index_timestamps: HashMap::new(),
                registry_crate_timestamps: HashMap::new(),
                registry_src_timestamps: HashMap::new(),
                git_db_timestamps: HashMap::new(),
                git_checkout_timestamps: HashMap::new(),
                save_err_has_warned: false,
                now: now(),
            }
        }

        pub fn is_empty(&self) -> bool {
            self.registry_index_timestamps.is_empty()
                && self.registry_crate_timestamps.is_empty()
                && self.registry_src_timestamps.is_empty()
                && self.git_db_timestamps.is_empty()
                && self.git_checkout_timestamps.is_empty()
        }

        fn clear(&mut self) {
            self.registry_index_timestamps.clear();
            self.registry_crate_timestamps.clear();
            self.registry_src_timestamps.clear();
            self.git_db_timestamps.clear();
            self.git_checkout_timestamps.clear();
        }

        /// Indicates the given [`RegistryIndex`] has been used right now.
        pub fn mark_registry_index_used(&mut self, registry_index: RegistryIndex) {
            self.mark_registry_index_used_stamp(registry_index, None);
        }

        /// Indicates the given [`RegistryCrate`] has been used right now.
        ///
        /// Also implicitly marks the index used, too.
        pub fn mark_registry_crate_used(&mut self, registry_crate: RegistryCrate) {
            self.mark_registry_crate_used_stamp(registry_crate, None);
        }

        /// Indicates the given [`RegistrySrc`] has been used right now.
        ///
        /// Also implicitly marks the index used, too.
        pub fn mark_registry_src_used(&mut self, registry_src: RegistrySrc) {
            self.mark_registry_src_used_stamp(registry_src, None);
        }

        /// Indicates the given [`GitCheckout`] has been used right now.
        ///
        /// Also implicitly marks the git db used, too.
        pub fn mark_git_checkout_used(&mut self, git_checkout: GitCheckout) {
            self.mark_git_checkout_used_stamp(git_checkout, None);
        }

        /// Indicates the given [`RegistryIndex`] has been used with the given
        /// time (or "now" if `None`).
        pub fn mark_registry_index_used_stamp(
            &mut self,
            registry_index: RegistryIndex,
            timestamp: Option<&SystemTime>,
        ) {
            let timestamp = timestamp.map_or(self.now, to_timestamp);
            self.registry_index_timestamps
                .insert(registry_index, timestamp);
        }

        /// Indicates the given [`RegistryCrate`] has been used with the given
        /// time (or "now" if `None`).
        ///
        /// Also implicitly marks the index used, too.
        pub fn mark_registry_crate_used_stamp(
            &mut self,
            registry_crate: RegistryCrate,
            timestamp: Option<&SystemTime>,
        ) {
            let timestamp = timestamp.map_or(self.now, to_timestamp);
            let index = RegistryIndex {
                encoded_registry_name: registry_crate.encoded_registry_name,
            };
            self.registry_index_timestamps.insert(index, timestamp);
            self.registry_crate_timestamps
                .insert(registry_crate, timestamp);
        }

        /// Indicates the given [`RegistrySrc`] has been used with the given
        /// time (or "now" if `None`).
        ///
        /// Also implicitly marks the index used, too.
        pub fn mark_registry_src_used_stamp(
            &mut self,
            registry_src: RegistrySrc,
            timestamp: Option<&SystemTime>,
        ) {
            let timestamp = timestamp.map_or(self.now, to_timestamp);
            let index = RegistryIndex {
                encoded_registry_name: registry_src.encoded_registry_name,
            };
            self.registry_index_timestamps.insert(index, timestamp);
            self.registry_src_timestamps.insert(registry_src, timestamp);
        }

        /// Indicates the given [`GitCheckout`] has been used with the given
        /// time (or "now" if `None`).
        ///
        /// Also implicitly marks the git db used, too.
        pub fn mark_git_checkout_used_stamp(
            &mut self,
            git_checkout: GitCheckout,
            timestamp: Option<&SystemTime>,
        ) {
            let timestamp = timestamp.map_or(self.now, to_timestamp);
            let db = GitDb {
                encoded_git_name: git_checkout.encoded_git_name,
            };
            self.git_db_timestamps.insert(db, timestamp);
            self.git_checkout_timestamps.insert(git_checkout, timestamp);
        }

        /// Saves all of the deferred information to the database.
        ///
        /// This will also clear the state of `self`.
        #[tracing::instrument(skip_all)]
        pub fn save(&mut self, tracker: &mut GlobalCacheTracker) -> CargoResult<()> {
            trace!(target: "gc", "saving last-use data");
            if self.is_empty() {
                return Ok(());
            }
            let tx = tracker.conn.transaction()?;
            // These must run before the ones that refer to their IDs.
            self.insert_registry_index_from_cache(&tx)?;
            self.insert_git_db_from_cache(&tx)?;
            self.insert_registry_crate_from_cache(&tx)?;
            self.insert_registry_src_from_cache(&tx)?;
            self.insert_git_checkout_from_cache(&tx)?;
            tx.commit()?;
            trace!(target: "gc", "last-use save complete");
            Ok(())
        }

        /// Variant of [`DeferredGlobalLastUse::save`] that does not return an
        /// error.
        ///
        /// This will log or display a warning to the user.
        pub fn save_no_error(&mut self, gctx: &GlobalContext) {
            if let Err(e) = self.save_with_gctx(gctx) {
                // Because there is an assertion in auto-gc that checks if this is
                // empty, be sure to clear it so that assertion doesn't fail.
                self.clear();
                if !self.save_err_has_warned {
                    if is_silent_error(&e) && gctx.shell().verbosity() != Verbosity::Verbose {
                        tracing::warn!("failed to save last-use data: {e:?}");
                    } else {
                        crate::display_warning_with_error(
                            "failed to save last-use data\n\
                            This may prevent cargo from accurately tracking what is being \
                            used in its global cache. This information is used for \
                            automatically removing unused data in the cache.",
                            &e,
                            &mut gctx.shell(),
                        );
                        self.save_err_has_warned = true;
                    }
                }
            }
        }

        fn save_with_gctx(&mut self, gctx: &GlobalContext) -> CargoResult<()> {
            let mut tracker = gctx.global_cache_tracker()?;
            self.save(&mut tracker)
        }

        /// Flushes all of the `registry_index_timestamps` to the database,
        /// clearing `registry_index_timestamps`.
        fn insert_registry_index_from_cache(&mut self, conn: &Connection) -> CargoResult<()> {
            insert_or_update_parent!(
                self,
                conn,
                "registry_index",
                registry_index_timestamps,
                registry_keys,
                encoded_registry_name
            );
        }

        /// Flushes all of the `git_db_timestamps` to the database,
        /// clearing `registry_index_timestamps`.
        fn insert_git_db_from_cache(&mut self, conn: &Connection) -> CargoResult<()> {
            insert_or_update_parent!(
                self,
                conn,
                "git_db",
                git_db_timestamps,
                git_keys,
                encoded_git_name
            );
        }

        /// Flushes all of the `registry_crate_timestamps` to the database,
        /// clearing `registry_index_timestamps`.
        fn insert_registry_crate_from_cache(&mut self, conn: &Connection) -> CargoResult<()> {
            let registry_crate_timestamps = std::mem::take(&mut self.registry_crate_timestamps);
            for (registry_crate, timestamp) in registry_crate_timestamps {
                trace!(target: "gc", "insert registry crate {registry_crate:?} {timestamp}");
                let registry_id = self.registry_id(conn, registry_crate.encoded_registry_name)?;
                let mut stmt = conn.prepare_cached(
                    "INSERT INTO registry_crate (registry_id, name, size, timestamp)
                     VALUES (?1, ?2, ?3, ?4)
                     ON CONFLICT DO UPDATE SET timestamp=excluded.timestamp
                        WHERE timestamp < ?5
                     ",
                )?;
                stmt.execute(params![
                    registry_id,
                    registry_crate.crate_filename,
                    registry_crate.size,
                    timestamp,
                    timestamp - UPDATE_RESOLUTION
                ])?;
            }
            Ok(())
        }

        /// Flushes all of the `registry_src_timestamps` to the database,
        /// clearing `registry_index_timestamps`.
        fn insert_registry_src_from_cache(&mut self, conn: &Connection) -> CargoResult<()> {
            let registry_src_timestamps = std::mem::take(&mut self.registry_src_timestamps);
            for (registry_src, timestamp) in registry_src_timestamps {
                trace!(target: "gc", "insert registry src {registry_src:?} {timestamp}");
                let registry_id = self.registry_id(conn, registry_src.encoded_registry_name)?;
                let mut stmt = conn.prepare_cached(
                    "INSERT INTO registry_src (registry_id, name, size, timestamp)
                     VALUES (?1, ?2, ?3, ?4)
                     ON CONFLICT DO UPDATE SET timestamp=excluded.timestamp
                        WHERE timestamp < ?5
                     ",
                )?;
                stmt.execute(params![
                    registry_id,
                    registry_src.package_dir,
                    registry_src.size,
                    timestamp,
                    timestamp - UPDATE_RESOLUTION
                ])?;
            }

            Ok(())
        }

        /// Flushes all of the `git_checkout_timestamps` to the database,
        /// clearing `registry_index_timestamps`.
        fn insert_git_checkout_from_cache(&mut self, conn: &Connection) -> CargoResult<()> {
            let git_checkout_timestamps = std::mem::take(&mut self.git_checkout_timestamps);
            for (git_checkout, timestamp) in git_checkout_timestamps {
                let git_id = self.git_id(conn, git_checkout.encoded_git_name)?;
                let mut stmt = conn.prepare_cached(
                    "INSERT INTO git_checkout (git_id, name, size, timestamp)
                     VALUES (?1, ?2, ?3, ?4)
                     ON CONFLICT DO UPDATE SET timestamp=excluded.timestamp
                        WHERE timestamp < ?5",
                )?;
                stmt.execute(params![
                    git_id,
                    git_checkout.short_name,
                    git_checkout.size,
                    timestamp,
                    timestamp - UPDATE_RESOLUTION
                ])?;
            }

            Ok(())
        }

        /// Returns the numeric ID of the registry, either fetching from the local
        /// cache, or getting it from the database.
        ///
        /// It is an error if the registry does not exist.
        fn registry_id(
            &mut self,
            conn: &Connection,
            encoded_registry_name: InternedString,
        ) -> CargoResult<ParentId> {
            match self.registry_keys.get(&encoded_registry_name) {
                Some(i) => Ok(*i),
                None => {
                    let Some(id) = GlobalCacheTracker::id_from_name(
                        conn,
                        REGISTRY_INDEX_TABLE,
                        &encoded_registry_name,
                    )?
                    else {
                        bail!("expected registry_index {encoded_registry_name} to exist, but wasn't found");
                    };
                    self.registry_keys.insert(encoded_registry_name, id);
                    Ok(id)
                }
            }
        }

        /// Returns the numeric ID of the git db, either fetching from the local
        /// cache, or getting it from the database.
        ///
        /// It is an error if the git db does not exist.
        fn git_id(
            &mut self,
            conn: &Connection,
            encoded_git_name: InternedString,
        ) -> CargoResult<ParentId> {
            match self.git_keys.get(&encoded_git_name) {
                Some(i) => Ok(*i),
                None => {
                    let Some(id) =
                        GlobalCacheTracker::id_from_name(conn, GIT_DB_TABLE, &encoded_git_name)?
                    else {
                        bail!("expected git_db {encoded_git_name} to exist, but wasn't found")
                    };
                    self.git_keys.insert(encoded_git_name, id);
                    Ok(id)
                }
            }
        }
    }

    /// Converts a [`SystemTime`] to a [`Timestamp`] which can be stored in the database.
    fn to_timestamp(t: &SystemTime) -> Timestamp {
        t.duration_since(SystemTime::UNIX_EPOCH)
            .expect("invalid clock")
            .as_secs()
    }

    /// Returns the current time.
    ///
    /// This supports pretending that the time is different for testing using an
    /// environment variable.
    ///
    /// If possible, try to avoid calling this too often since accessing clocks
    /// can be a little slow on some systems.
    #[allow(clippy::disallowed_methods)]
    fn now() -> Timestamp {
        match std::env::var("__CARGO_TEST_LAST_USE_NOW") {
            Ok(now) => now.parse().unwrap(),
            Err(_) => to_timestamp(&SystemTime::now()),
        }
    }

    /// Returns whether or not the given error should cause a warning to be
    /// displayed to the user.
    ///
    /// In some situations, like a read-only global cache, we don't want to spam
    /// the user with a warning. I think once cargo has controllable lints, I
    /// think we should consider changing this to always warn, but give the user
    /// an option to silence the warning.
    pub fn is_silent_error(e: &anyhow::Error) -> bool {
        if let Some(e) = e.downcast_ref::<rusqlite::Error>() {
            if matches!(
                e.sqlite_error_code(),
                Some(ErrorCode::CannotOpen | ErrorCode::ReadOnly)
            ) {
                return true;
            }
        }
        false
    }

    /// Returns the disk usage for a git checkout directory.
    #[tracing::instrument]
    fn du_git_checkout(path: &Path) -> CargoResult<u64> {
        // !.git is used because clones typically use hardlinks for the git
        // contents. TODO: Verify behavior on Windows.
        // TODO: Or even better, switch to worktrees, and remove this.
        cargo_util::du(&path, &["!.git"])
    }

    fn du(path: &Path, table_name: &str) -> CargoResult<u64> {
        if table_name == GIT_CO_TABLE {
            du_git_checkout(path)
        } else {
            cargo_util::du(&path, &[])
        }
    }