The planner classifies operations involved in a query as either parallel safe, parallel restricted, or parallel unsafe. A parallel safe operation is one which does not conflict with the use of parallel query. A parallel restricted operation is one which cannot be performed in a parallel worker, but which can be performed in the leader while parallel query is in use. Therefore, parallel restricted operations can never occur below a Gather node, but can occur elsewhere in a plan which contains a

Because each worker executes the parallel portion of the plan to completion, it is not possible to simply take an ordinary query plan and run it using multiple workers. Each worker would produce a full copy of the output result set, so the query would not run any faster than normal but would produce incorrect results. Instead, the parallel portion of the plan must be what is known internally to the query optimizer as a partial plan; that is, it must constructed so that each process will which e

PostgreSQL supports basic table partitioning. This section describes why and how to implement partitioning as part of your database design. 5.10.1. Overview Partitioning refers to splitting what is logically one large table into smaller physical pieces. Partitioning can provide several benefits: Query performance can be improved dramatically in certain situations, particularly when most of the heavily accessed rows of the table are in a single partition or a small number of partitions. The pa

The passwordcheck module checks users' passwords whenever they are set with CREATE ROLE or ALTER ROLE. If a password is considered too weak, it will be rejected and the command will terminate with an error. To enable this module, add '$libdir/passwordcheck' to shared_preload_libraries in postgresql.conf, then restart the server. You can adapt this module to your needs by changing the source code. For example, you can use CrackLib to check passwords — this only requires uncommenting two lines in

After a query has produced an output table (after the select list has been processed) it can optionally be sorted. If sorting is not chosen, the rows will be returned in an unspecified order. The actual order in that case will depend on the scan and join plan types and the order on disk, but it must not be relied on. A particular output ordering can only be guaranteed if the sort step is explicitly chosen. The ORDER BY clause specifies the sort order: SELECT select_list FROM table_expressi

The pageinspect module provides functions that allow you to inspect the contents of database pages at a low level, which is useful for debugging purposes. All of these functions may be used only by superusers. F.22.1. Functions get_raw_page(relname text, fork text, blkno int) returns bytea get_raw_page reads the specified block of the named relation and returns a copy as a bytea value. This allows a single time-consistent copy of the block to be obtained. fork should be 'main' for th

An index definition can specify an operator class for each column of an index. CREATE INDEX name ON table (column opclass [sort options] [, ...]); The operator class identifies the operators to be used by the index for that column. For example, a B-tree index on the type int4 would use the int4_ops class; this operator class includes comparison functions for values of type int4. In practice the default operator class for the column's data type is usually sufficient. The main reason for having

Object identifiers (OIDs) are used internally by PostgreSQL as primary keys for various system tables. OIDs are not added to user-created tables, unless WITH OIDS is specified when the table is created, or the default_with_oids configuration variable is enabled. Type oid represents an object identifier. There are also several alias types for oid: regproc, regprocedure, regoper, regoperator, regclass, regtype, regrole, regnamespace, regconfig, and regdictionary. Table 8-24 shows an overview. The

Numeric types consist of two-, four-, and eight-byte integers, four- and eight-byte floating-point numbers, and selectable-precision decimals. Table 8-2 lists the available types. Table 8-2. Numeric Types Name Storage Size Description Range smallint 2 bytes small-range integer -32768 to +32767 integer 4 bytes typical choice for integer -2147483648 to +2147483647 bigint 8 bytes large-range integer -9223372036854775808 to +9223372036854775807 decimal variable user-specified precision, exact up

Table 9-36 shows the operators available for the cidr and inet types. The operators <<, <<=, >>, >>=, and && test for subnet inclusion. They consider only the network parts of the two addresses (ignoring any host part) and determine whether one network is identical to or a subnet of the other. Table 9-36. cidr and inet Operators Operator Description Example < is less than inet '192.168.1.5' < inet '192.168.1.6' <= is less than or equal inet '192.168.1.