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       REINDEX - rebuild indexes




       REINDEX  rebuilds  an  index  based  on  the data stored in the index’s
       table, replacing the old copy of the index. There are two main  reasons
       to use REINDEX:

       · An  index  has  become  corrupted, and no longer contains valid data.
         Although in theory this should never happen, in practice indexes  may
         become  corrupted  due to software bugs or hardware failures. REINDEX
         provides a recovery method.

       · The index in question contains a lot of dead index pages that are not
         being  reclaimed.  This  can  occur with B-tree indexes in PostgreSQL
         under certain 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 the documentation for more information.


              Recreate all system indexes of a specified database. Indexes  on
              user  tables  are  not processed. Also, indexes on shared system
              catalogs are skipped except in stand-alone mode (see below).

       TABLE  Recreate all indexes of a specified table. If the  table  has  a
              secondary ‘‘TOAST’’ table, that is reindexed as well.

       INDEX  Recreate a specified index.

       name   The  name  of  the  specific  database,  table,  or  index to be
              reindexed.  Table  and  index  names  may  be  schema-qualified.
              Presently,   REINDEX  DATABASE  can  only  reindex  the  current
              database, so its parameter must  match  the  current  database’s

       FORCE  This is an obsolete option; it is ignored if specified.


       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

       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 may 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 postmaster and start a stand-
       alone PostgreSQL server with the -P  option  included  on  its  command
       issued, depending on how much you want to reconstruct. If in doubt, use
       REINDEX  DATABASE to select reconstruction of all system indexes in the
       database. Then quit the  standalone  server  session  and  restart  the
       regular   server.    See   the  postgres(1)  reference  page  for  more
       information  about  how  to  interact  with  the   stand-alone   server

       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
       may still be wise to prevent other users from connecting to the damaged
       database until repairs have been completed.

       If  corruption  is suspected in the indexes of any of the shared system
       catalogs (pg_database, pg_group, pg_shadow, or pg_tablespace),  then  a
       standalone  server  must be used to repair it. REINDEX will not process
       shared catalogs in multiuser mode.

       For all indexes except the shared system catalogs,  REINDEX  is  crash-
       safe  and  transaction-safe.  REINDEX  is  not  crash-safe  for  shared
       indexes, which is why this case is disallowed during normal  operation.
       If  a  failure  occurs  while  reindexing  one  of  these  catalogs  in
       standalone mode, it will not be possible to restart the regular  server
       until  the  problem  is  rectified. (The typical symptom of a partially
       rebuilt shared index is ‘‘index is not a btree’’ errors.)

       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 exclusive lock on
       the specific index being processed, which will block reads that attempt
       to  use that index. In contrast, DROP INDEX momentarily takes 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 may be forced into expensive sequential scans.
       Another important point is that the  drop/create  approach  invalidates
       any cached query plans that use the index, while REINDEX does not.

       Prior  to  PostgreSQL  7.4, REINDEX TABLE did not automatically process
       TOAST tables, and so those had to be reindexed  by  separate  commands.
       This is still possible, but redundant.


       Recreate the indexes on the table my_table:

       REINDEX TABLE my_table;

       Rebuild a single index:

       REINDEX INDEX my_index;

       Rebuild  all  system indexes in a particular database, without trusting
       them to be valid already:

       $ export PGOPTIONS="-P"
       $ psql broken_db
       broken_db=> REINDEX DATABASE broken_db;
       broken_db=> \q


       There is no REINDEX command in the SQL standard.