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Mention "PostgreSQL"'s hashes as slower/similar to btree.

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This commit is contained in:
Bruce Momjian 2002-06-21 19:06:44 +00:00
parent 1415a8388f
commit dad0e20f29
3 changed files with 23 additions and 19 deletions
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20
doc/src/sgml/diskusage.sgml
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@ -1,5 +1,5 @@
<!--
$Header: /cvsroot/pgsql/doc/src/sgml/diskusage.sgml,v 1.1 2002/06/13 05:15:22 momjian Exp $
$Header: /cvsroot/pgsql/doc/src/sgml/diskusage.sgml,v 1.2 2002/06/21 19:06:44 momjian Exp $
-->
<chapter id="diskusage">
@ -22,10 +22,12 @@ $Header: /cvsroot/pgsql/doc/src/sgml/diskusage.sgml,v 1.1 2002/06/13 05:15:22 mo
</para>
<para>
You can monitor disk space from two places; from inside
<application>psql</> and from the command line using
<application>contrib/oid2name</>. Using <application>psql</> you can
issue queries to see the disk usage for any table:
You can monitor disk space from three places: from
<application>psql</> using <command>VACUUM</> information, from
<application>psql</> using <application>contrib/dbsize</>, and from
the command line using <application>contrib/oid2name</>. Using
<application>psql</> on a recently vacuumed (or analyzed) database,
you can issue queries to see the disk usage of any table:
<programlisting>
play=# SELECT relfilenode, relpages
play-# FROM pg_class
@ -38,10 +40,10 @@ play-# WHERE relname = 'customer';
</para>
<para>
Each page is typically 8 kilobytes. <literal>relpages</> is only
updated by <command>VACUUM</> and <command>ANALYZE</>. To show the
space used by <acronym>TOAST</> tables, use a query based on the heap
relfilenode:
Each page is typically 8 kilobytes. (Remember, <literal>relpages</>
is only updated by <command>VACUUM</> and <command>ANALYZE</>.) To
show the space used by <acronym>TOAST</> tables, use a query based on
the heap relfilenode shown above:
<programlisting>
play=# SELECT relname, relpages
play-# FROM pg_class

11
doc/src/sgml/indices.sgml
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@ -1,4 +1,4 @@
<!-- $Header: /cvsroot/pgsql/doc/src/sgml/indices.sgml,v 1.33 2002/06/21 16:52:00 momjian Exp $ -->
<!-- $Header: /cvsroot/pgsql/doc/src/sgml/indices.sgml,v 1.34 2002/06/21 19:06:44 momjian Exp $ -->
<chapter id="indexes">
<title id="indexes-title">Indexes</title>
@ -181,10 +181,11 @@ CREATE INDEX <replaceable>name</replaceable> ON <replaceable>table</replaceable>
</synopsis>
<note>
<para>
Testing has shown hash indexes to be similar or slower than btree
indexes, and the index size and build time for hash indexes is much
worse. Hash indexes also suffer poor performance under high
concurrency. For these reasons, hash index use is discouraged.
Testing has shown PostgreSQL's hash indexes to be similar or slower
than btree indexes, and the index size and build time for hash
indexes is much worse. Hash indexes also suffer poor performance
under high concurrency. For these reasons, hash index use is
discouraged.
</para>
</note>
</para>

11
doc/src/sgml/ref/create_index.sgml
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@ -1,5 +1,5 @@
<!--
$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_index.sgml,v 1.33 2002/06/21 16:52:00 momjian Exp $
$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_index.sgml,v 1.34 2002/06/21 19:06:44 momjian Exp $
PostgreSQL documentation
-->
@ -330,10 +330,11 @@ ERROR: Cannot create index: 'index_name' already exists.
the <literal>=</literal> operator.
</para>
<para>
Testing has shown hash indexes to be similar or slower than btree
indexes, and the index size and build time for hash indexes is much
worse. Hash indexes also suffer poor performance under high
concurrency. For these reasons, hash index use is discouraged.
Testing has shown PostgreSQL's hash indexes to be similar or slower
than btree indexes, and the index size and build time for hash
indexes is much worse. Hash indexes also suffer poor performance
under high concurrency. For these reasons, hash index use is
discouraged.
</para>
<para>