Improve Redshift support documentation.

Author: dimitri

docs/index.rst

@@ -24,8 +24,7 @@ Welcome to pgloader's documentation!
    ref/mssql
    ref/pgsql
    ref/pgsql-citus-target
-   ref/pgsql-redshift-source
-   ref/pgsql-redshift-target
+   ref/pgsql-redshift
    ref/transforms
    bugreport
 

docs/intro.rst

@@ -10,10 +10,13 @@ the data into the server, and manages errors by filling a pair of
 pgloader knows how to read data from different kind of sources:
 
   * Files
+
     * CSV
     * Fixed Format
     * DBF
+
   * Databases
+
     * SQLite
     * MySQL
     * MS SQL Server

docs/ref/pgsql-redshift-source.rst

@@ -0,0 +1,70 @@
+Support for Redshift in pgloader
+================================
+
+The command and behavior are the same as when migration from a PostgreSQL
+database source. pgloader automatically discovers that it's talking to a
+Redshift database by parsing the output of the `SELECT version()` SQL query.
+
+Redhift as a data source
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+Redshit 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.