REINDEX { TABLE | DATABASE | INDEX } name [ FORCE ]
Recreate all indexes of a specified table.
Recreate all system indexes of a specified database. (User-table indexes are not included.)
Recreate a specified index.
The name of the specific table/database/index to be reindexed. Table and index names may be schema-qualified.
Force rebuild of system indexes. Without this keyword REINDEX skips system indexes that are not marked invalid. FORCE is irrelevant for REINDEX INDEX, or when reindexing user indexes.
REINDEX is used to rebuild corrupted indexes. Although in theory this should never be necessary, in practice indexes may become corrupted due to software bugs or hardware failures. REINDEX provides a recovery method.
REINDEX also removes certain dead index pages that can't be reclaimed any other way. See the "Routine Reindexing" section in the manual for more information.
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.
Note: Another approach to dealing with a corrupted user-table index is just to drop and recreate it. This may in fact be preferable if you would like to maintain some semblance of normal operation on the table meanwhile. REINDEX acquires exclusive lock on the table, while CREATE INDEX only locks out writes not reads of the 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 backend doing the recovery to not have used any of the suspect indexes itself. (Indeed, in this sort of scenario you may find that backends are crashing immediately at start-up, due to reliance on the corrupted indexes.) To recover safely, the postmaster must be shut down and a stand-alone PostgreSQL backend must be started instead, giving it the command-line options -O and -P (these options allow system table modifications and prevent use of system indexes, respectively). Then issue REINDEX INDEX, REINDEX TABLE, or REINDEX DATABASE depending on how much you want to reconstruct. If in doubt, use REINDEX DATABASE FORCE to force reconstruction of all system indexes in the database. Then quit the standalone backend and restart the postmaster.
Since this is likely the only situation when most people will ever use a standalone backend, some usage notes might be in order:
Start the backend with a command like
postgres -D $PGDATA -O -P my_database
Provide the correct path to the database area with
-D, or make sure that the
environment variable PGDATA is set.
Also specify the name of the particular database you want to
work in.
You can issue any SQL command, not only REINDEX.
Be aware that the standalone backend treats newline as the command entry terminator; there is no intelligence about semicolons, as there is in psql. To continue a command across multiple lines, you must type backslash just before each newline except the last one. Also, you won't have any of the conveniences of command-line editing (no command history, for example).
To quit the backend, type EOF (Control+D, usually).
See the postgres reference page for more information.