Provided by: postgresql-client-8.4_8.4.4-2_i386 bug

NAME

       ANALYZE - collect statistics about a database

SYNOPSIS

       ANALYZE [ VERBOSE ] [ table [ ( column [, ...] ) ] ]

DESCRIPTION

       ANALYZE  collects  statistics  about  the  contents  of  tables  in the
       database, and stores the results in the  pg_statistic  system  catalog.
       Subsequently, the query planner uses these statistics to help determine
       the most efficient execution plans for queries.

       With  no  parameter,  ANALYZE  examines  every  table  in  the  current
       database.  With  a  parameter,  ANALYZE examines only that table. It is
       further possible to give a list of column names, in which case only the
       statistics for those columns are collected.

PARAMETERS

       VERBOSE
              Enables display of progress messages.

       table  The  name  (possibly  schema-qualified)  of  a specific table to
              analyze. Defaults to all tables in the current database.

       column The name of a  specific  column  to  analyze.  Defaults  to  all
              columns.

OUTPUTS

       When  VERBOSE is specified, ANALYZE emits progress messages to indicate
       which table is currently being processed. Various statistics about  the
       tables are printed as well.

NOTES

       In  the  default  PostgreSQL  configuration, in the documentation takes
       care of automatic analyzing of tables when they are first  loaded  with
       data, and as they change throughout regular operation.  When autovacuum
       is disabled, it is a good idea to run  ANALYZE  periodically,  or  just
       after  making  major  changes  in  the  contents  of  a table. Accurate
       statistics will help the planner to choose the most  appropriate  query
       plan,  and  thereby  improve  the  speed  of query processing. A common
       strategy is to run VACUUM [vacuum(7)] and ANALYZE once a day  during  a
       low-usage time of day.

       ANALYZE requires only a read lock on the target table, so it can run in
       parallel with other activity on the table.

       The statistics collected by ANALYZE usually include a list of  some  of
       the  most  common  values  in  each  column and a histogram showing the
       approximate data distribution in each column. One or both of these  can
       be  omitted  if  ANALYZE  deems  them  uninteresting (for example, in a
       unique-key column, there are no common values) or if  the  column  data
       type  does  not  support  the  appropriate  operators.  There  is  more
       information about the statistics in in the documentation.

       For large tables, ANALYZE takes a random sample of the table  contents,
       rather  than examining every row. This allows even very large tables to
       be analyzed in  a  small  amount  of  time.  Note,  however,  that  the
       statistics  are  only  approximate,  and will change slightly each time
       ANALYZE is run, even if the actual table contents did not change.  This
       might result in small changes in the planner’s estimated costs shown by
       EXPLAIN [explain(7)].  In rare situations,  this  non-determinism  will
       cause  the  planner’s choices of query plans to change after ANALYZE is
       run.  To avoid this,  raise  the  amount  of  statistics  collected  by
       ANALYZE, as described below.

       The   extent   of   analysis   can   be  controlled  by  adjusting  the
       default_statistics_target configuration variable, or  on  a  column-by-
       column  basis  by  setting  the per-column statistics target with ALTER
       TABLE  ...  ALTER  COLUMN  ...  SET   STATISTICS   (see   ALTER   TABLE
       [alter_table(7)]).  The target value sets the maximum number of entries
       in the most-common-value list and the maximum number  of  bins  in  the
       histogram. The default target value is 100, but this can be adjusted up
       or down to trade off accuracy of planner  estimates  against  the  time
       taken  for ANALYZE and the amount of space occupied in pg_statistic. In
       particular, setting the statistics target to zero  disables  collection
       of  statistics  for  that  column.  It  might  be useful to do that for
       columns that are never used as part of the WHERE, GROUP BY, or ORDER BY
       clauses  of  queries, since the planner will have no use for statistics
       on such columns.

       The  largest  statistics  target  among  the  columns  being   analyzed
       determines  the number of table rows sampled to prepare the statistics.
       Increasing the target causes a proportional increase in  the  time  and
       space needed to do ANALYZE.

COMPATIBILITY

       There is no ANALYZE statement in the SQL standard.

SEE ALSO

       VACUUM  [vacuum(7)],  vacuumdb  [vacuumdb(1)], in the documentation, in
       the documentation