Introduction
============

pgloader loads data from various sources into PostgreSQL. It can
transform the data it reads on the fly and submit raw SQL before and
after the loading.  It uses the `COPY` PostgreSQL protocol to stream
the data into the server, and manages errors by filling a pair of
*reject.dat* and *reject.log* files.

pgloader knows how to read data from different kind of sources:

  * Files

    * CSV
    * Fixed Format
    * DBF

  * Databases

    * SQLite
    * MySQL
    * MS SQL Server
    * PostgreSQL
    * Redshift

pgloader knows how to target different products using the PostgresQL Protocol:

  * PostgreSQL
  * `Citus <https://www.citusdata.com>`_
  * Redshift

The level of automation provided by pgloader depends on the data source
type. In the case of CSV and Fixed Format files, a full description of the
expected input properties must be given to pgloader. In the case of a
database, pgloader connects to the live service and knows how to fetch the
metadata it needs directly from it.

Features Matrix
---------------

Here's a comparison of the features supported depending on the source
database engine. Some features that are not supported can be added to
pgloader, it's just that nobody had the need to do so yet. Those features
are marked with ✗. Empty cells are used when the feature doesn't make sense
for the selected source database.

==========================   =======  ======  ======  ===========  =========
Feature                      SQLite   MySQL   MS SQL  PostgreSQL   Redshift 
==========================   =======  ======  ======  ===========  =========
One-command migration           ✓       ✓       ✓           ✓          ✓
Continuous Migration            ✓       ✓       ✓           ✓          ✓
Schema discovery                ✓       ✓       ✓           ✓          ✓
Partial Migrations              ✓       ✓       ✓           ✓          ✓
Schema only                     ✓       ✓       ✓           ✓          ✓
Data only                       ✓       ✓       ✓           ✓          ✓
Repeatable (DROP+CREATE)        ✓       ✓       ✓           ✓          ✓
User defined casting rules      ✓       ✓       ✓           ✓          ✓
Encoding Overrides                      ✓
On error stop                   ✓       ✓       ✓           ✓          ✓
On error resume next            ✓       ✓       ✓           ✓          ✓
Pre/Post SQL commands           ✓       ✓       ✓           ✓          ✓
Post-Schema SQL commands        ✗       ✓       ✓           ✓          ✓
Primary key support             ✓       ✓       ✓           ✓          ✓
Foreign key support             ✓       ✓       ✓           ✓
Online ALTER schema             ✓       ✓       ✓           ✓          ✓
Materialized views              ✗       ✓       ✓           ✓          ✓
Distribute to Citus             ✗       ✓       ✓           ✓          ✓
==========================   =======  ======  ======  ===========  =========

For more details about what the features are about, see the specific
reference pages for your database source.

For some of the features, missing support only means that the feature is not
needed for the other sources, such as the capability to override MySQL
encoding metadata about a table or a column. Only MySQL in this list is left
completely unable to guarantee text encoding. Or Redshift not having foreign
keys.


Commands
--------

pgloader implements its own *Command Language*, a DSL that allows to specify
every aspect of the data load and migration to implement. Some of the
features provided in the language are only available for a specific source
type.

Command Line
------------

The pgloader command line accepts those two variants::

    pgloader [<options>] [<command-file>]...
    pgloader [<options>] SOURCE TARGET

Either you have a *command-file* containing migration specifications in the
pgloader *Command Language*, or you can give a *Source* for the data and a
PostgreSQL database connection *Target* where to load the data into.
