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Cluster fixup.

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This commit is contained in:
Bruce Momjian 1998-03-14 22:55:21 +00:00
parent 3674ccdf95
commit 006fd9253f
1 changed files with 7 additions and 6 deletions
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src/man/cluster.l
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@ -1,6 +1,6 @@
.\" This is -*-nroff-*-
.\" XXX standard disclaimer belongs here....
.\" $Header: /cvsroot/pgsql/src/man/Attic/cluster.l,v 1.5 1998/03/14 21:57:56 momjian Exp $
.\" $Header: /cvsroot/pgsql/src/man/Attic/cluster.l,v 1.6 1998/03/14 22:55:21 momjian Exp $
.TH CLUSTER SQL 01/23/93 PostgreSQL PostgreSQL
.SH NAME
cluster - give storage clustering advice to Postgres
@ -48,11 +48,12 @@ unordered, the entries are on random pages, so there is one disk page
retrieved for every row moved. PostgreSQL has a cache, but the majority
of a big table will not fit in the cache.
.PP
Another way is to use SELECT ... INTO TABLE temp FROM ... This uses the
PostgreSQL sorting code, and is much faster for unordered data. You
then drop the old table, use ALTER TABLE RENAME to rename 'temp' to the
old name, and recreate the indexes. From then on, CLUSTER should be
fast because most of the heap data is ordered.
Another way is to use SELECT ... INTO TABLE temp FROM ...ORDER BY ...
This uses the PostgreSQL sorting code in ORDER BY to match the index,
and is much faster for unordered data. You then drop the old table, use
ALTER TABLE RENAME to rename 'temp' to the old name, and recreate the
indexes. From then on, CLUSTER should be fast because most of the heap
data has been already ordered.
.SH EXAMPLE
.nf
/*