Shared Disk Failover Shared disk failover avoids synchronization overhead by having only one copy of the database. It uses a single disk array that is shared by multiple servers. If the main database server fails, the standby server is able to mount and start the database as though it were recovering from a database crash. This allows rapid failover with no data loss. Shared hardware functionality is common in network storage devices. Using a network file system is also possible, though care

The catalog pg_aggregate stores information about aggregate functions. An aggregate function is a function that operates on a set of values (typically one column from each row that matches a query condition) and returns a single value computed from all these values. Typical aggregate functions are sum, count, and max. Each entry in pg_aggregate is an extension of an entry in pg_proc. The pg_proc entry carries the aggregate's name, input and output data types, and other information that is simil

NameCREATE INDEX -- define a new index Synopsis CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] [ [ IF NOT EXISTS ] name ] ON table_name [ USING method ] ( { column_name | ( expression ) } [ COLLATE collation ] [ opclass ] [ ASC | DESC ] [ NULLS { FIRST | LAST } ] [, ...] ) [ WITH ( storage_parameter = value [, ... ] ) ] [ TABLESPACE tablespace_name ] [ WHERE predicate ] Description CREATE INDEX constructs an index on the specified column(s) of the specified relation, which c

NameCREATE CONVERSION -- define a new encoding conversion Synopsis CREATE [ DEFAULT ] CONVERSION name FOR source_encoding TO dest_encoding FROM function_name Description CREATE CONVERSION defines a new conversion between character set encodings. Also, conversions that are marked DEFAULT can be used for automatic encoding conversion between client and server. For this purpose, two conversions, from encoding A to B and from encoding B to A, must be defined. To be able to create a co

CREATE DATABASE actually works by copying an existing database. By default, it copies the standard system database named template1. Thus that database is the "template" from which new databases are made. If you add objects to template1, these objects will be copied into subsequently created user databases. This behavior allows site-local modifications to the standard set of objects in databases. For example, if you install the procedural language PL/Perl in template1, it will automatically be a

NameALTER TEXT SEARCH CONFIGURATION -- change the definition of a text search configuration Synopsis ALTER TEXT SEARCH CONFIGURATION name ADD MAPPING FOR token_type [, ... ] WITH dictionary_name [, ... ] ALTER TEXT SEARCH CONFIGURATION name ALTER MAPPING FOR token_type [, ... ] WITH dictionary_name [, ... ] ALTER TEXT SEARCH CONFIGURATION name ALTER MAPPING REPLACE old_dictionary WITH new_dictionary ALTER TEXT SEARCH CONFIGURATION name ALTER MAPPING FOR token_type [, ... ]

A window function performs a calculation across a set of table rows that are somehow related to the current row. This is comparable to the type of calculation that can be done with an aggregate function. But unlike regular aggregate functions, use of a window function does not cause rows to become grouped into a single output row — the rows retain their separate identities. Behind the scenes, the window function is able to access more than just the current row of the query result. Here is an ex

Transactions are a fundamental concept of all database systems. The essential point of a transaction is that it bundles multiple steps into a single, all-or-nothing operation. The intermediate states between the steps are not visible to other concurrent transactions, and if some failure occurs that prevents the transaction from completing, then none of the steps affect the database at all. For example, consider a bank database that contains balances for various customer accounts, as well as tot

NameSET TRANSACTION -- set the characteristics of the current transaction Synopsis SET TRANSACTION transaction_mode [, ...] SET TRANSACTION SNAPSHOT snapshot_id SET SESSION CHARACTERISTICS AS TRANSACTION transaction_mode [, ...] where transaction_mode is one of: ISOLATION LEVEL { SERIALIZABLE | REPEATABLE READ | READ COMMITTED | READ UNCOMMITTED } READ WRITE | READ ONLY [ NOT ] DEFERRABLE Description The SET TRANSACTION command sets the characteristics of the current tra

NameCREATE RULE -- define a new rewrite rule Synopsis CREATE [ OR REPLACE ] RULE name AS ON event TO table_name [ WHERE condition ] DO [ ALSO | INSTEAD ] { NOTHING | command | ( command ; command ... ) } where event can be one of: SELECT | INSERT | UPDATE | DELETE Description CREATE RULE defines a new rule applying to a specified table or view. CREATE OR REPLACE RULE will either create a new rule, or replace an existing rule of the same name for the same table. The Postg