# Redshift to Postgres

The command and behavior are the same as when migration from a PostgreSQL database source, see Postgres to Postgres. pgloader automatically discovers that it’s talking to a Redshift database by parsing the output of the `SELECT version()` SQL query.

## Redshift as a data source

Redshift is a variant of PostgreSQL version 8.0.2, which allows pgloader to work with only a very small amount of adaptation in the catalog queries used. In other words, migrating from Redshift to PostgreSQL works just the same as when migrating from a PostgreSQL data source, including the connection string specification.

## Redshift as a data destination

The Redshift variant of PostgreSQL 8.0.2 does not have support for the `COPY FROM STDIN` feature that pgloader normally relies upon. To use COPY with Redshift, the data must first be made available in an S3 bucket.

First, pgloader must authenticate to Amazon S3. pgloader uses the following setup for that:

> - `~/.aws/config`

>   This INI formatted file contains sections with your default region and other global values relevant to using the S3 API. pgloader parses it to get the region when it’s setup in the `default` INI section.

>   The environment variable `AWS_DEFAULT_REGION` can be used to override the configuration file value.

> - `~/.aws/credentials`

>   The INI formatted file contains your authentication setup to Amazon, with the properties `aws_access_key_id` and `aws_secret_access_key` in the section `default`. pgloader parses this file for those keys, and uses their values when communicating with Amazon S3.

>   The environment variables `AWS_ACCESS_KEY_ID` and `AWS_SECRET_ACCESS_KEY` can be used to override the configuration file

> - `AWS_S3_BUCKET_NAME`

>   Finally, the value of the environment variable `AWS_S3_BUCKET_NAME` is used by pgloader as the name of the S3 bucket where to upload the files to COPY to the Redshift database. The bucket name defaults to `pgloader`.

Then pgloader works as usual, see the other sections of the documentation for the details, depending on the data source (files, other databases, etc). When preparing the data for PostgreSQL, pgloader now uploads each batch into a single CSV file, and then issue such as the following, for each batch:

    COPY <target_table_name>
          FROM 's3://<s3 bucket>/<s3-filename-just-uploaded>'
          FORMAT CSV
          TIMEFORMAT 'auto'
          REGION '<aws-region>'
          ACCESS_KEY_ID '<aws-access-key-id>'
          SECRET_ACCESS_KEY '<aws-secret-access-key>;

This is the only difference with a PostgreSQL core version, where pgloader can rely on the classic `COPY FROM STDIN` command, which allows to send data through the already established connection to PostgreSQL.