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REINDEX()			 SQL Commands			     REINDEX()

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:

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

       · 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.

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

       · 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  CONCUR‐
	 RENTLY 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 data‐
	      base.  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
	      transaction block.

       name   The  name	 of the specific index, table, or database to be rein‐
	      dexed.  Index  and  table	  names	  may	be   schema-qualified.
	      Presently,  REINDEX 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 may 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
       may 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_pltem‐
       plate, pg_shdepend, pg_shdescription, and pg_tablespace), then a stand‐
       alone 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 consider‐
       ations  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 may be forced into expensive sequential scans. Another  important
       point  is  that	the  drop/create approach invalidates any cached query
       plans that use the index, while REINDEX does not.

       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	avail‐
       able 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 sys‐
       tem 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	  2008-01-03			     REINDEX()
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