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 two main reasons 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.
· The index in question contains a lot of dead index pages that are not
being reclaimed. This can occur with B-tree indexes in PostgreSQL
under certain 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 the documentation for more information.
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).
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).
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 postmaster and start a stand-
alone PostgreSQL server with the -P option included on its command
line. Then, REINDEX DATABASE, REINDEX SYSTEM, REINDEX TABLE, or REIN‐
DEX 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 standalone server session and
restart the regular server. See the postgres(1) reference page for
more information about how to interact with the stand-alone 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, 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 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
Recreate the indexes on the table my_table:
REINDEX TABLE my_table;
Rebuild a single index:
REINDEX INDEX my_index;
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 2005-11-05 REINDEX()
