table of contents
| REINDEX(7) | PostgreSQL 13.18 Documentation | REINDEX(7) |
NAME¶
REINDEX - rebuild indexes
SYNOPSIS¶
REINDEX [ ( option [, ...] ) ] { INDEX | TABLE | SCHEMA | DATABASE | SYSTEM } [ CONCURRENTLY ] name
where option can be one of:
VERBOSE
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¶
INDEX
TABLE
SCHEMA
DATABASE
SYSTEM
name
CONCURRENTLY
For temporary tables, REINDEX is always non-concurrent, as no other session can access them, and non-concurrent reindex is cheaper.
VERBOSE
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.
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 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. Reindexing a schema or database requires being the owner of that schema or database. 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). Of course, superusers can always reindex anything.
Reindexing partitioned tables or partitioned indexes is not supported. Each individual partition can be reindexed separately instead.
Rebuilding Indexes Concurrently¶
Rebuilding an index can interfere with regular operation of a database. Normally PostgreSQL locks the table whose index is rebuilt against writes and performs the entire index build with a single scan of the table. Other transactions can still read the table, but if they try to insert, update, or delete rows in the table they will block until the index rebuild is finished. This could have a severe effect if the system is a live production database. Very large tables can take many hours to be indexed, and even for smaller tables, an index rebuild can lock out writers for periods that are unacceptably long for a production system.
PostgreSQL supports rebuilding indexes with minimum locking of writes. This method is invoked by specifying the CONCURRENTLY option of REINDEX. When this option is used, PostgreSQL must perform two scans of the table for each index that needs to be rebuilt and wait for termination of all existing transactions that could potentially use the index. This method requires more total work than a standard index rebuild and takes significantly longer to complete as it needs to wait for unfinished transactions that might modify the index. However, since it allows normal operations to continue while the index is being rebuilt, this method is useful for rebuilding indexes in a production environment. Of course, the extra CPU, memory and I/O load imposed by the index rebuild may slow down other operations.
The following steps occur in a concurrent reindex. Each step is run in a separate transaction. If there are multiple indexes to be rebuilt, then each step loops through all the indexes before moving to the next step.
If a problem arises while rebuilding the indexes, such as a uniqueness violation in a unique index, the REINDEX command will fail but leave behind an “invalid” new index in addition to the pre-existing one. This index will be ignored for querying purposes because it might be incomplete; however it will still consume update overhead. The psql \d command will report such an index as INVALID:
postgres=# \d tab
Table "public.tab"
Column | Type | Modifiers --------+---------+-----------
col | integer | Indexes:
"idx" btree (col)
"idx_ccnew" btree (col) INVALID
If the index marked INVALID is suffixed ccnew, then it corresponds to the transient index created during the concurrent operation, and the recommended recovery method is to drop it using DROP INDEX, then attempt REINDEX CONCURRENTLY again. If the invalid index is instead suffixed ccold, it corresponds to the original index which could not be dropped; the recommended recovery method is to just drop said index, since the rebuild proper has been successful.
Regular index builds permit other regular index builds on the same table to occur simultaneously, but only one concurrent index build can occur on a table at a time. In both cases, no other types of schema modification on the table are allowed meanwhile. Another difference is that a regular REINDEX TABLE or REINDEX INDEX command can be performed within a transaction block, but REINDEX CONCURRENTLY cannot.
Like any long-running transaction, REINDEX on a table can affect which tuples can be removed by concurrent VACUUM on any other table.
REINDEX SYSTEM does not support CONCURRENTLY since system catalogs cannot be reindexed concurrently.
Furthermore, indexes for exclusion constraints cannot be reindexed concurrently. If such an index is named directly in this command, an error is raised. If a table or database with exclusion constraint indexes is reindexed concurrently, those indexes will be skipped. (It is possible to reindex such indexes without the CONCURRENTLY option.)
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¶
CREATE INDEX (CREATE_INDEX(7)), DROP INDEX (DROP_INDEX(7)), reindexdb(1)
| 2024 | PostgreSQL 13.18 |