The pgrowlocks module provides a function to show row locking information for a specified table. F.28.1. Overview pgrowlocks(text) returns setof record The parameter is the name of a table. The result is a set of records, with one row for each locked row within the table. The output columns are shown in Table F-21. Table F-21. pgrowlocks Output Columns Name Type Description locked_row tid Tuple ID (TID) of locked row locker xid Transaction ID of locker, or multixact ID if multitransaction

The pgcrypto module provides cryptographic functions for PostgreSQL. F.25.1. General Hashing Functions F.25.1.1. digest() digest(data text, type text) returns bytea digest(data bytea, type text) returns bytea Computes a binary hash of the given data. type is the algorithm to use. Standard algorithms are md5, sha1, sha224, sha256, sha384 and sha512. If pgcrypto was built with OpenSSL, more algorithms are available, as detailed in Table F-20. If you want the digest as a hexadecimal string, u

Namepgbench -- run a benchmark test on PostgreSQL Synopsis pgbench -i [option...] [dbname] pgbench [option...] [dbname] Description pgbench is a simple program for running benchmark tests on PostgreSQL. It runs the same sequence of SQL commands over and over, possibly in multiple concurrent database sessions, and then calculates the average transaction rate (transactions per second). By default, pgbench tests a scenario that is loosely based on TPC-B, involving five SELECT, UPDATE, and

As we saw in the previous section, the query planner needs to estimate the number of rows retrieved by a query in order to make good choices of query plans. This section provides a quick look at the statistics that the system uses for these estimates. One component of the statistics is the total number of entries in each table and index, as well as the number of disk blocks occupied by each table and index. This information is kept in the table pg_class, in the columns reltuples and relpages. W

One might need to insert a large amount of data when first populating a database. This section contains some suggestions on how to make this process as efficient as possible. 14.4.1. Disable Autocommit When using multiple INSERTs, turn off autocommit and just do one commit at the end. (In plain SQL, this means issuing BEGIN at the start and COMMIT at the end. Some client libraries might do this behind your back, in which case you need to make sure the library does it when you want it done.) If

Durability is a database feature that guarantees the recording of committed transactions even if the server crashes or loses power. However, durability adds significant database overhead, so if your site does not require such a guarantee, PostgreSQL can be configured to run much faster. The following are configuration changes you can make to improve performance in such cases. Except as noted below, durability is still guaranteed in case of a crash of the database software; only abrupt operating

PostgreSQL devises a query plan for each query it receives. Choosing the right plan to match the query structure and the properties of the data is absolutely critical for good performance, so the system includes a complex planner that tries to choose good plans. You can use the EXPLAIN command to see what query plan the planner creates for any query. Plan-reading is an art that requires some experience to master, but this section attempts to cover the basics. Examples in this section are drawn

It is possible to control the query planner to some extent by using the explicit JOIN syntax. To see why this matters, we first need some background. In a simple join query, such as: SELECT * FROM a, b, c WHERE a.id = b.id AND b.ref = c.id; the planner is free to join the given tables in any order. For example, it could generate a query plan that joins A to B, using the WHERE condition a.id = b.id, and then joins C to this joined table, using the other WHERE condition. Or it could join B to C

There are three separate approaches to pattern matching provided by PostgreSQL: the traditional SQL LIKE operator, the more recent SIMILAR TO operator (added in SQL:1999), and POSIX-style regular expressions. Aside from the basic "does this string match this pattern?" operators, functions are available to extract or replace matching substrings and to split a string at matching locations. Tip: If you have pattern matching needs that go beyond this, consider writing a user-defined function in P

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