# Command Syntax

pgloader implements a Domain Specific Language allowing to setup complex data loading scripts handling computed columns and on-the-fly sanitization of the input data. For more complex data loading scenarios, you will be required to learn that DSL’s syntax. It’s meant to look familiar to DBA by being inspired by SQL where it makes sense, which is not that much after all.

The pgloader commands follow the same global grammar rules. Each of them might support only a subset of the general options and provide specific options.

    LOAD <source-type>
             FROM <source-url>
           [ HAVING FIELDS <source-level-options> ]
                 INTO <postgresql-url>
           [ TARGET TABLE [ "<schema>" ]."<table name>" ]
           [ TARGET COLUMNS <columns-and-options> ]

        [ WITH <load-options> ]

        [ SET <postgresql-settings> ]

    [ BEFORE LOAD [ DO <sql statements> | EXECUTE <sql file> ] ... ]
    [  AFTER LOAD [ DO <sql statements> | EXECUTE <sql file> ] ... ]
        ;

The main clauses are the LOAD, FROM, INTO and WITH clauses that each command implements. Some command then implement the SET command, or some specific clauses such as the CAST clause.

## Command Clauses

The pgloader command syntax allows composing CLAUSEs together. Some clauses are specific to the FROM source-type, most clauses are always available.

## FROM

The FROM clause specifies where to read the data from, and each command introduces its own variant of sources. For instance, the CSV source supports inline, stdin, a filename, a quoted filename, and a FILENAME MATCHING clause (see above); whereas the MySQL source only supports a MySQL database URI specification.

## INTO

The PostgreSQL connection URI must contains the name of the target table where to load the data into. That table must have already been created in PostgreSQL, and the name might be schema qualified.

Then INTO option also supports an optional comma separated list of target columns, which are either the name of an input field or the white space separated list of the target column name, its PostgreSQL data type and a USING expression.

The USING expression can be any valid Common Lisp form and will be read with the current package set to pgloader.transforms, so that you can use functions defined in that package, such as functions loaded dynamically with the –load command line parameter.

Each USING expression is compiled at runtime to native code.

This feature allows pgloader to load any number of fields in a CSV file into a possibly different number of columns in the database, using custom code for that projection.

## WITH

Set of options to apply to the command, using a global syntax of either:

> - key = value

> - use option

> - do not use option

See each specific command for details.

All data sources specific commands support the following options:

> - on error stop, on error resume next

> - batch rows = R

> - batch size = … MB

> - prefetch rows = …

See the section BATCH BEHAVIOUR OPTIONS for more details.

In addition, the following settings are available:

> - workers = W

> - concurrency = C

> - max parallel create index = I

See section A NOTE ABOUT PARALLELISM for more details.

## SET

This clause allows to specify session parameters to be set for all the sessions opened by pgloader. It expects a list of parameter name, the equal sign, then the single-quoted value as a comma separated list.

The names and values of the parameters are not validated by pgloader, they are given as-is to PostgreSQL.

## BEFORE LOAD DO

You can run SQL queries against the database before loading the data from the CSV file. Most common SQL queries are CREATE TABLE IF NOT EXISTS so that the data can be loaded.

Each command must be dollar-quoted: it must begin and end with a double dollar sign, $$. Dollar-quoted queries are then comma separated. No extra punctuation is expected after the last SQL query.

## BEFORE LOAD EXECUTE

Same behaviour as in the BEFORE LOAD DO clause. Allows you to read the SQL queries from a SQL file. Implements support for PostgreSQL dollar-quoting and the i and ir include facilities as in psql batch mode (where they are the same thing).

## AFTER LOAD DO

Same format as BEFORE LOAD DO, the dollar-quoted queries found in that section are executed once the load is done. That’s the right time to create indexes and constraints, or re-enable triggers.

## AFTER LOAD EXECUTE

Same behaviour as in the AFTER LOAD DO clause. Allows you to read the SQL queries from a SQL file. Implements support for PostgreSQL dollar-quoting and the i and ir include facilities as in psql batch mode (where they are the same thing).

## AFTER CREATE SCHEMA DO

Same format as BEFORE LOAD DO, the dollar-quoted queries found in that section are executed once the schema has been created by pgloader, and before the data is loaded. It’s the right time to ALTER TABLE or do some custom implementation on-top of what pgloader does, like maybe partitioning.

## AFTER CREATE SCHEMA EXECUTE

Same behaviour as in the AFTER CREATE SCHEMA DO clause. Allows you to read the SQL queries from a SQL file. Implements support for PostgreSQL dollar-quoting and the i and ir include facilities as in psql batch mode (where they are the same thing).

## Connection String

The <postgresql-url> parameter is expected to be given as a Connection URI as documented in the PostgreSQL documentation at http://www.postgresql.org/docs/9.3/static/libpq-connect.html#LIBPQ-CONNSTRING.

    postgresql://[user[:password]@][netloc][:port][/dbname][?option=value&...]

Where:

> - user

>   Can contain any character, including colon (:) which must then be doubled (::) and at-sign (@) which must then be doubled (@@).

>   When omitted, the user name defaults to the value of the PGUSER environment variable, and if it is unset, the value of the USER environment variable.

> - password

>   > Can contain any character, including the at sign (@) which must then be doubled (@@). To leave the password empty, when the user name ends with at at sign, you then have to use the syntax user:@.

>   When omitted, the password defaults to the value of the PGPASSWORD environment variable if it is set, otherwise the password is left unset.

>   When no password is found either in the connection URI nor in the environment, then pgloader looks for a .pgpass file as documented at https://www.postgresql.org/docs/current/static/libpq-pgpass.html. The implementation is not that of libpq though. As with libpq you can set the environment variable PGPASSFILE to point to a .pgpass file, and pgloader defaults to ~/.pgpass on unix like systems and %APPDATA%postgresqlpgpass.conf on windows. Matching rules and syntax are the same as with libpq, refer to its documentation.

> - netloc

>   Can be either a hostname in dotted notation, or an ipv4, or an Unix domain socket path. Empty is the default network location, under a system providing unix domain socket that method is preferred, otherwise the netloc default to localhost.

>   > It’s possible to force the unix domain socket path by using the syntax unix:/path/to/where/the/socket/file/is, so to force a non default socket path and a non default port, you would have:

>   > > postgresql://unix:/tmp:54321/dbname

>   The netloc defaults to the value of the PGHOST environment variable, and if it is unset, to either the default unix socket path when running on a Unix system, and localhost otherwise.

>   Socket path containing colons are supported by doubling the colons within the path, as in the following example:

>   > postgresql://unix:/tmp/project::region::instance:5432/dbname

> - dbname

>   > Should be a proper identifier (letter followed by a mix of letters, digits and the punctuation signs comma (,), dash (-) and underscore (_).

>   When omitted, the dbname defaults to the value of the environment variable PGDATABASE, and if that is unset, to the user value as determined above.

> - options

>   The optional parameters must be supplied with the form name=value, and you may use several parameters by separating them away using an ampersand (&) character.

>   Only some options are supported here, tablename (which might be qualified with a schema name) sslmode, host, port, dbname, user and password.

>   The sslmode parameter values can be one of disable, allow, prefer or require.

>   For backward compatibility reasons, it’s possible to specify the tablename option directly, without spelling out the tablename= parts.

>   The options override the main URI components when both are given, and using the percent-encoded option parameters allow using passwords starting with a colon and bypassing other URI components parsing limitations.

## Regular Expressions

Several clauses listed in the following accept regular expressions with the following input rules:

> - A regular expression begins with a tilde sign (~),

> - is then followed with an opening sign,

> - then any character is allowed and considered part of the regular expression, except for the closing sign,

> - then a closing sign is expected.

The opening and closing sign are allowed by pair, here’s the complete list of allowed delimiters:

    ~//
    ~[]
    ~{}
    ~()
    ~<>
    ~""
    ~''
    ~||
    ~##

Pick the set of delimiters that don’t collide with the regular expression you’re trying to input. If your expression is such that none of the solutions allow you to enter it, the places where such expressions are allowed should allow for a list of expressions.

## Comments

Any command may contain comments, following those input rules:

> - the – delimiter begins a comment that ends with the end of the current line,

> - the delimiters /* and */ respectively start and end a comment, which can be found in the middle of a command or span several lines.

Any place where you could enter a whitespace will accept a comment too.

## Batch behaviour options

All pgloader commands have support for a WITH clause that allows for specifying options. Some options are generic and accepted by all commands, such as the batch behaviour options, and some options are specific to a data source kind, such as the CSV skip header option.

The global batch behaviour options are:

> - batch rows

>   Takes a numeric value as argument, used as the maximum number of rows allowed in a batch. The default is 25 000 and can be changed to try having better performance characteristics or to control pgloader memory usage;

> - batch size

>   Takes a memory unit as argument, such as 20 MB, its default value. Accepted multipliers are kB, MB, GB, TB and PB. The case is important so as not to be confused about bits versus bytes, we’re only talking bytes here.

> - prefetch rows

>   Takes a numeric value as argument, defaults to 100000. That’s the number of rows that pgloader is allowed to read in memory in each reader thread. See the workers setting for how many reader threads are allowed to run at the same time.

Other options are specific to each input source, please refer to specific parts of the documentation for their listing and covering.

A batch is then closed as soon as either the batch rows or the batch size threshold is crossed, whichever comes first. In cases when a batch has to be closed because of the batch size setting, a debug level log message is printed with how many rows did fit in the oversized batch.

## Templating with Mustache

pgloader implements the https://mustache.github.io/ templating system so that you may have dynamic parts of your commands. See the documentation for this template system online.

A specific feature of pgloader is the ability to fetch a variable from the OS environment of the pgloader process, making it possible to run pgloader as in the following example:

    $ DBPATH=sqlite/sqlite.db pgloader ./test/sqlite-env.load

or in several steps:

    $ export DBPATH=sqlite/sqlite.db
    $ pgloader ./test/sqlite-env.load

The variable can then be used in a typical mustache fashion:

    load database
         from '{{DBPATH}}'
         into postgresql:///pgloader;

It’s also possible to prepare a INI file such as the following:

    [pgloader]

    DBPATH = sqlite/sqlite.db

And run the following command, feeding the INI values as a context for pgloader templating system:

    $ pgloader --context ./test/sqlite.ini ./test/sqlite-ini.load

The mustache templates implementation with OS environment support replaces former GETENV implementation, which didn’t work anyway.