CLUSTER micro-doc-patch
Started by Sergey E. Koposovabout 19 years ago2 messages
Hello All,
Doing recently the CLUSTER operation with (SELECT .. ORDER BY ...) instead
of CLUSTER I realized that that operation requires the free space equal to
twice! the size of the table size :-( (which is unfortunately a serious
drawback of the SELECT method, comparing to the plain CLUSTER for
the large tables )...
So, I send the small doc-patch saying about the space requirement of the
cluster operation using SELECT ORDER BY.
Regards,
Sergey
*******************************************************************
Sergey E. Koposov
Max Planck Institute for Astronomy/Sternberg Astronomical Institute
Tel: +49-6221-528-349
Web: http://lnfm1.sai.msu.ru/~math
E-mail: math@sai.msu.ru
Attachments:
cluster-doc.patchtext/plain; charset=US-ASCII; name=cluster-doc.patchDownload
Index: doc/src/sgml/ref/cluster.sgml
===================================================================
RCS file: /projects/cvsroot/pgsql/doc/src/sgml/ref/cluster.sgml,v
retrieving revision 1.37
diff -c -r1.37 cluster.sgml
*** doc/src/sgml/ref/cluster.sgml 31 Oct 2006 01:52:31 -0000 1.37
--- doc/src/sgml/ref/cluster.sgml 4 Nov 2006 13:14:19 -0000
***************
*** 153,160 ****
which uses the <productname>PostgreSQL</productname> sorting code in
the <literal>ORDER BY</literal> clause to create the desired order; this is usually much
! faster than an index scan for
! unordered data. You then drop the old table, use
<command>ALTER TABLE ... RENAME</command>
to rename <replaceable class="parameter">newtable</replaceable> to the old name, and
recreate the table's indexes. However, this approach does not preserve
--- 153,161 ----
which uses the <productname>PostgreSQL</productname> sorting code in
the <literal>ORDER BY</literal> clause to create the desired order; this is usually much
! faster than an index scan for unordered data (during that operation, you
! need free space on disk at least equal to two times the table size).
! You then drop the old table, use
<command>ALTER TABLE ... RENAME</command>
to rename <replaceable class="parameter">newtable</replaceable> to the old name, and
recreate the table's indexes. However, this approach does not preserve
