REINDEX(7) PostgreSQL 15.7 Documentation REINDEX(7)
NAME
REINDEX - rebuild indexes
SYNOPSIS
REINDEX [ ( option [, ...] ) ] { INDEX | TABLE | SCHEMA | DATABASE | SYSTEM } [ CONCURRENTLY ] name
where option can be one of:
CONCURRENTLY [ boolean ]
TABLESPACE new_tablespace
VERBOSE [ boolean ]
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
can become corrupted due to software bugs or hardware failures.
REINDEX provides a recovery method.
• An index has become “bloated”, that is it 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
Section 25.2 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.
• If an index build fails with the CONCURRENTLY option, this index is
left as “invalid”. Such indexes are useless but it can be
convenient to use REINDEX to rebuild them. Note that only REINDEX
INDEX is able to perform a concurrent build on an invalid index.
PARAMETERS
INDEX
Recreate the specified index. This form of REINDEX cannot be
executed inside a transaction block when used with a partitioned
index.
TABLE
Recreate all indexes of the specified table. If the table has a
secondary “TOAST” table, that is reindexed as well. This form of
REINDEX cannot be executed inside a transaction block when used
with a partitioned table.
SCHEMA
Recreate all indexes of the specified schema. If a table of this
schema has a secondary “TOAST” table, that is reindexed as well.
Indexes on shared system catalogs are also processed. This form of
REINDEX cannot be executed inside a transaction block.
DATABASE
Recreate all indexes within the current database. Indexes on shared
system catalogs are also processed. This form of REINDEX cannot be
executed inside a transaction block.
SYSTEM
Recreate all indexes on system catalogs within the current
database. Indexes on shared system catalogs are included. Indexes
on user tables are not processed. This form of REINDEX cannot be
executed inside a transaction block.
name
The name of the specific index, table, or database to be reindexed.
Index and table names can 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.
CONCURRENTLY
When this option is used, PostgreSQL will rebuild the index without
taking any locks that prevent concurrent inserts, updates, or
deletes on the table; whereas a standard index rebuild locks out
writes (but not reads) on the table until it's done. There are
several caveats to be aware of when using this option — see
Rebuilding Indexes Concurrently below.
For temporary tables, REINDEX is always non-concurrent, as no other
session can access them, and non-concurrent reindex is cheaper.
TABLESPACE
Specifies that indexes will be rebuilt on a new tablespace.
VERBOSE
Prints a progress report as each index is reindexed.
boolean
Specifies whether the selected option should be turned on or off.
You can write TRUE, ON, or 1 to enable the option, and FALSE, OFF,
or 0 to disable it. The boolean value can also be omitted, in which
case TRUE is assumed.
new_tablespace
The tablespace where indexes will be rebuilt.
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 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. 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 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.
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.
1. A new transient index definition is added to the catalog pg_index.
This definition will be used to replace the old index. A SHARE
UPDATE EXCLUSIVE lock at session level is taken on the indexes
being reindexed as well as their associated tables to prevent any
schema modification while processing.
2. A first pass to build the index is done for each new index. Once
the index is built, its flag pg_index.indisready is switched to
“true” to make it ready for inserts, making it visible to other
sessions once the transaction that performed the build is finished.
This step is done in a separate transaction for each index.
3. Then a second pass is performed to add tuples that were added while
the first pass was running. This step is also done in a separate
transaction for each index.
4. All the constraints that refer to the index are changed to refer to
the new index definition, and the names of the indexes are changed.
At this point, pg_index.indisvalid is switched to “true” for the
new index and to “false” for the old, and a cache invalidation is
done causing all sessions that referenced the old index to be
invalidated.
5. The old indexes have pg_index.indisready switched to “false” to
prevent any new tuple insertions, after waiting for running queries
that might reference the old index to complete.
6. The old indexes are dropped. The SHARE UPDATE EXCLUSIVE session
locks for the indexes and the table are released.
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.)
Each backend running REINDEX will report its progress in the
pg_stat_progress_create_index view. See Section 28.4.2 for details.
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), Section 28.4.2
PostgreSQL 15.7 2024 REINDEX(7)
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