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PostgreSQL Database Module

Features

Here is a quick list of what's different in the Postgres module (a full description follows afterwards):

  • T-Search
  • Extended index support
  • Array data types
  • Transactions
  • Table partitioning
  • Tablespaces
  • Index clustering

If you don't know much about databases, or don't want to use any of the advanced features that this module provides, then you don't need to read any further.

The use of any of these features, especially the advanced options, implies that you have some level of comfort in administrating a Postgres database.

T-Search

T-Search support is provided via both GiST and GIN. You can cluster and search columns with combinations of these methods. It is up to you to decide which is most appropriate for your data.

The dev/build process automatically creates a special column on each table, and a trigger is automatically set up to update this column whenever the targeted columns are changed. T-Search uses this column to return matches for search criteria.

Please see tutorial 4 for information how to enable fulltext search and the necessary controller hooks.

Extended index support

Indexes have been extended to include support for more options. These new options include:

  • The ability to specify index methods (btree/hash/). Btree is probably fine nearly all indexes, and it is the default. 'Unique' is also supported.
  • Partial indexes. This is especially handy for creating an index while i gnoring nulls or default data.
  • Multiple column indexing. If your WHERE clauses always use the same columns, then you can create one index covering all of these at once.
  • Fill factor. If your table content is static, then you can reduce the physical disk space your index uses. Also, if you use clustering, giving the fillfactor a low number may help performance for updates.

Examples:

Hash index:

public static $indexes = array( 'Address'=>Array('type'=>'hash', 'name'=>'Address'), );

Where clause:

public static $indexes = array( 'Address'=>Array('type'=>'unique', 'name'=>'Address', 'where'=>""Address" IS NOT NULL"), );

Fill factor:

public static $indexes = array( 'Address'=>Array('type'=>'unique', 'name'=>'Address', 'fillfactor'=>'50'), );

Array data types

Nearly all data types in SilverStripe can now be expressed as an array. For example, you can specify an int as this:

$db = array ( 'Quantity'=>'Int[]' )

You would populate this like so:

$item->Quantity='Array[1,2,3...]';

It also takes object literals if you're more familiar with that or it suits your purpose better, like this:

$item->Quantity='{1,2,3}';

Using arrays as data types means that you can avoid join tables. This is not recommended if the SilverStripe ORM would expect a has_one or has_many etc under normal circumstances, but it could be useful in the case where you have a very large join table. You can also index these arrays with GIN indexes.

Please consult the official Postgres documentation for more information.

Transactions

Transactions are supported at the database connection level. The relevant functions are:

  • DB::get_conn()→startTransaction($transaction_mode, $session_characteristics)
  • DB::get_conn()→transactionSavepoint($name)
  • DB::get_conn()→transactionRollback($savepoint)
  • DB::get_conn()→endTransaction();

You can create a savepoint by passing a name to the function, and then rollback either all of the uncommited transactions, or if you pass a savepoint name, jump back to the point you'd prefer.

$transaction_mode and $session_characteristic take the full range of isolation levels supported by Postgres.

Please consult the official Postgres documentation for more information.

Table Partitioning

This is an experimental feature.

If you have a very large table, you can split it into many child tables. The advantages of this depend on your particular situation. Generally speaking, if your table is very large, queries should be faster.

You can create a partitioned table like this:

public static $database_extensions = array( 'partitions'=>array( 'child_table_1'=>'NEW."ID">0 AND NEW."ID"<=100', 'child_table_2'=>'NEW."ID">100 AND NEW."ID"<=200' ) );

'NEW.' is a required part of the configuration string.

Partitioning should be set up right from the beginning. Partitioning a table which already has data may have unpredictable results.

Please consult the official Postgres documentation for more information.

Tablespaces

This is an experimental feature.

Tablespaces are good for moving the physical files to a faster device (or slower and less used if that's a better option). You can set up a tablespace like this:

public static $database_extensions = array( 'tablespace'=>Array('name'=>'fastspace', 'location'=>'/faster_location'), );

The '/faster_location' path must be owned by the postgres user. If you try to delete a tablespace via the 'drop tablespace' command, then this directory must be empty.

Changing the location of the tablespace through the SilverStripe $database_extensions array will cause the dev/build process to attempt to delete the old location. An error message will be displayed if this location is not empty.

Please consult the official Postgres documentation for more information.

Index Clustering

This is an experimental feature.

Index clustering allows you to reorganise the way rows are ordered inside a table according to an index specification. This can be a very intensive disk operation. You specify an index cluster like this:

public static $database_extensions = array( 'cluster'=>'index_name' );

Clustering is only applied on a table on the second instance of a dev/build command being run on it (running a cluster command on an empty table is pointless).

Clustering needs to be reapplied on a regular basis if you're updating this table. You can also decrease the fillfactor on that index as well for potential performance gains.

As an alternative, clustering isn't necessary if you rebuild a table with an ORDER BY clause, where the ORDER BY column is the same as what you'd be clustering it by. The dev/build process does not do table rebuilds, so this is something you'd have to do yourself.

Please consult the official Postgres documentation for more information.

A note about these advanced features

The advanced features are here as an experimental offering. They have not been fully tested and their functionality and purpose may change in the future. They are primarily here to offer the ability to handle very large datasets.

They are also features which require the user to be very familiar with both Postgres and how their data works. If you can't predict how your database will be populated, then most of these features will be of little use.

User contributed information

Provided by dompie

If you want to install this on a more secure postgresql server, go to PostgreSQLDatabase.php and set "public static $check_database_exists = false;"

Moreover you have to replace in PostgreSQLDatabaseConfigurationHelper.php occurrences of

$connstring = "host=$server port=5432 dbname=postgres {$userPart}{$passwordPart}";

with

$dbname = $databaseConfig['database']?$databaseConfig['database']: 'postgres'; $connstring = "host=$server port=5432 dbname=$dbname {$userPart}{$passwordPart}";

Otherwise this extension will try to connect to "postgres" Database to check DB connection, no matter what you entered in the "Database Name" field during installation.

Make sure you have set the "search_path" correct for your database user.