REINDEX

REINDEX

7

SQL - Language Statements

REINDEX

rebuild indexes

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 [???](#routine-reindex) 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 MDASH see
    [Rebuilding Indexes Concurrently](#sql-reindex-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 [???](#app-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. 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 {#sql-reindex-concurrently}
-------------------------------

index

rebuilding 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.
Excepted from this are operations with the `CONCURRENTLY` option for
indexes that are not partial and do not index any expressions.

`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
[???](#create-index-progress-reporting) 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
========
