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:

Parameters

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 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.

REINDEX is similar to a drop and recreate of the index in that the index contents are rebuilt from scratch. However, the locking considerations are rather different. REINDEX locks out writes but not reads of the index's parent table. It also takes an ACCESS EXCLUSIVE lock on the specific index being processed, which will block reads that attempt to use that index. In particular, the query planner tries to take an ACCESS SHARE lock on every index of the table, regardless of the query, and so REINDEX blocks virtually any queries except for some prepared queries whose plan has been cached and which don't use this very index. In contrast, DROP INDEX momentarily takes an ACCESS 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, having privileges of the pg_maintain role, or having the MAINTAIN privilege on the table. Reindexing a schema or database requires being the owner of that schema or database or having privileges of the pg_maintain role. Note specifically that it's thus possible for non-superusers to rebuild indexes of tables owned by other users. However, as a special exception, when REINDEX DATABASE, REINDEX SCHEMA or REINDEX SYSTEM is issued by a non-superuser, indexes on shared catalogs will be skipped unless the user owns the catalog (which typically won't be the case), has privileges of the pg_maintain role, or has the MAINTAIN privilege on the catalog. If a role has permission to REINDEX a partitioned table, it is also permitted to REINDEX each of its partitions, regardless of whether the role has the aforementioned privileges on the partition. Of course, superusers can always reindex anything.

Reindexing partitioned indexes or partitioned tables is supported with REINDEX INDEX or REINDEX TABLE, respectively. Each partition of the specified partitioned relation is reindexed in a separate transaction. Those commands cannot be used inside a transaction block when working on a partitioned table or index.

When using the TABLESPACE clause with REINDEX on a partitioned index or table, only the tablespace references of the leaf partitions are updated. As partitioned indexes are not updated, it is recommended to separately use ALTER TABLE ONLY on them so as any new partitions attached inherit the new tablespace. On failure, it may not have moved all the indexes to the new tablespace. Re-running the command will rebuild all the leaf partitions and move previously-unprocessed indexes to the new tablespace.

If SCHEMA, DATABASE or SYSTEM is used with TABLESPACE, system relations are skipped and a single WARNING will be generated. Indexes on TOAST tables are rebuilt, but not moved to the new tablespace.

postgres=# \d tab
       Table "public.tab"
 Column |  Type   | Modifiers
--------+---------+-----------
 col    | integer |
Indexes:
    "idx" btree (col)
    "idx_ccnew" btree (col) INVALID

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

Rebuild indexes for a table, without blocking read and write operations on involved relations while reindexing is in progress:

REINDEX TABLE CONCURRENTLY my_broken_table;

Compatibility

There is no REINDEX command in the SQL standard.

See Also