REINDEX(7)							   SQL Commands 							REINDEX(7)

NAME

       REINDEX - rebuild indexes

SYNOPSIS

       REINDEX { INDEX | TABLE | DATABASE | SYSTEM } name [ FORCE ]

DESCRIPTION

       REINDEX	rebuilds  an index using the data stored in the index's table, replacing the old copy of the index. There are several scenarios in
       which to use REINDEX:

       o An index has become corrupted, and no longer contains valid data. Although in theory this should never happen, in  practice  indexes  can
	 become corrupted due to software bugs or hardware failures. REINDEX provides a recovery method.

       o An  index  has become ``bloated'', that it is contains many empty or nearly-empty pages. This can occur with B-tree indexes in PostgreSQL
	 under certain uncommon access patterns. REINDEX provides a way to reduce the space consumption of the index by writing a new  version	of
	 the index without the dead pages. See in the documentation for more information.

       o You have altered a storage parameter (such as fillfactor) for an index, and wish to ensure that the change has taken full effect.

       o An  index  build  with the CONCURRENTLY option failed, leaving an ``invalid'' index. Such indexes are useless but it can be convenient to
	 use REINDEX to rebuild them. Note that REINDEX will not perform a concurrent build. To build the index without interfering  with  produc-
	 tion you should drop the index and reissue the CREATE INDEX CONCURRENTLY command.

PARAMETERS

       INDEX  Recreate the specified index.

       TABLE  Recreate all indexes of the specified table. If the table has a secondary ``TOAST'' table, that is reindexed as well.

       DATABASE
	      Recreate	all  indexes  within  the current database.  Indexes on shared system catalogs are skipped except in stand-alone mode (see
	      below). This form of REINDEX cannot be executed inside a transaction block.

       SYSTEM Recreate all indexes on system catalogs within the current database.  Indexes on user tables are not  processed.	Also,  indexes	on
	      shared  system catalogs are skipped except in stand-alone mode (see below).  This form of REINDEX cannot be executed inside a trans-
	      action block.

       name   The name of the specific index, table, or database to be reindexed. Index and table names can be schema-qualified.  Presently, REIN-
	      DEX DATABASE and REINDEX SYSTEM can only reindex the current database, so their parameter must match the current database's name.

       FORCE  This is an obsolete option; it is ignored if specified.

NOTES

       If  you suspect corruption of an index on a user table, you can simply rebuild that index, or all indexes on the table, using REINDEX INDEX
       or REINDEX TABLE.

       Things are more difficult if you need to recover from corruption of an index on a system table. In this case it's important for the  system
       to  not	have  used any of the suspect indexes itself.  (Indeed, in this sort of scenario you might find that server processes are crashing
       immediately at start-up, due to reliance on the corrupted indexes.) To recover safely, the server must be started with the -P option, which
       prevents it from using indexes for system catalog lookups.

       One  way  to  do this is to shut down the server and start a single-user PostgreSQL server with the -P option included on its command line.
       Then, REINDEX DATABASE, REINDEX SYSTEM, REINDEX TABLE, or REINDEX INDEX can be issued, depending on how much you want to reconstruct. If in
       doubt,  use  REINDEX  SYSTEM  to  select reconstruction of all system indexes in the database. Then quit the single-user server session and
       restart the regular server.  See the postgres(1) reference page for more information about how to  interact  with  the  single-user  server
       interface.

       Alternatively,  a  regular  server  session  can be started with -P included in its command line options.  The method for doing this varies
       across clients, but in all libpq-based clients, it is possible to set the PGOPTIONS environment variable to -P before starting the  client.
       Note  that  while  this method does not require locking out other clients, it might still be wise to prevent other users from connecting to
       the damaged database until repairs have been completed.

       If corruption is suspected in the indexes of any of  the  shared  system  catalogs  (which  are	pg_authid,  pg_auth_members,  pg_database,
       pg_pltemplate,  pg_shdepend,  pg_shdescription,	and  pg_tablespace),  then a standalone server must be used to repair it. REINDEX will not
       process shared catalogs in multiuser mode.

       For all indexes except the shared system catalogs, REINDEX is crash-safe  and  transaction-safe.  REINDEX  is  not  crash-safe  for  shared
       indexes, which is why this case is disallowed during normal operation. If a failure occurs while reindexing one of these catalogs in stand-
       alone mode, it will not be possible to restart the regular server until the problem is rectified.  (The	typical  symptom  of  a  partially
       rebuilt shared index is ``index is not a btree'' errors.)

       REINDEX is similar to a drop and recreate of the index in that the index contents are rebuilt from scratch. However, the locking considera-
       tions are rather different. REINDEX locks out writes but not reads of the index's parent table. It also takes an exclusive lock on the spe-
       cific  index  being  processed,	which will block reads that attempt to use that index. In contrast, DROP INDEX momentarily takes exclusive
       lock on the parent table, blocking both writes and reads. The subsequent CREATE INDEX locks out writes but not reads; since  the  index	is
       not  there,  no	read  will  attempt  to use it, meaning that there will be no blocking but reads might be forced into expensive sequential
       scans.

       Reindexing a single index or table requires being the owner of that index or table. Reindexing a database requires being the owner  of  the
       database  (note that the owner can therefore rebuild indexes of tables owned by other users). Of course, superusers can always reindex any-
       thing.

       Prior to PostgreSQL 8.1, REINDEX DATABASE processed only system indexes, not all indexes as one would expect from the name. This  has  been
       changed to reduce the surprise factor. The old behavior is available as REINDEX SYSTEM.

       Prior  to  PostgreSQL 7.4, REINDEX TABLE did not automatically process TOAST tables, and so those had to be reindexed by separate commands.
       This is still possible, but redundant.

EXAMPLES

       Rebuild a single index:

       REINDEX INDEX my_index;

       Rebuild all the indexes on the table my_table:

       REINDEX TABLE my_table;

       Rebuild all indexes in a particular database, without trusting the system indexes to be valid already:

       $ export PGOPTIONS="-P"
       $ psql broken_db
       broken_db=> REINDEX DATABASE broken_db;
       broken_db=> q

COMPATIBILITY

       There is no REINDEX command in the SQL standard.

SQL - Language Statements					    2010-05-14								REINDEX(7)