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| author | Bruce Momjian <bruce@momjian.us> | 2002-06-21 03:25:53 +0000 |
|---|---|---|
| committer | Bruce Momjian <bruce@momjian.us> | 2002-06-21 03:25:53 +0000 |
| commit | ebe4375fa1d875ff51dbc127f3317d281b21589d (patch) | |
| tree | ce1a086dc544499c9bb81c0cb66e71104ac97a4d /doc/src | |
| parent | db650b451ed4dcacc1022d9bfbcc36ca383257f1 (diff) | |
| download | postgresql-ebe4375fa1d875ff51dbc127f3317d281b21589d.tar.gz postgresql-ebe4375fa1d875ff51dbc127f3317d281b21589d.zip | |
Document problems with hash indexes compared to btree.
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/indices.sgml | 11 | ||||
| -rw-r--r-- | doc/src/sgml/ref/create_index.sgml | 7 | ||||
| -rw-r--r-- | doc/src/sgml/xindex.sgml | 8 |
3 files changed, 14 insertions, 12 deletions
diff --git a/doc/src/sgml/indices.sgml b/doc/src/sgml/indices.sgml index 417a50dcb35..6317e4ea749 100644 --- a/doc/src/sgml/indices.sgml +++ b/doc/src/sgml/indices.sgml @@ -1,4 +1,4 @@ -<!-- $Header: /cvsroot/pgsql/doc/src/sgml/indices.sgml,v 1.31 2002/01/07 02:29:12 petere Exp $ --> +<!-- $Header: /cvsroot/pgsql/doc/src/sgml/indices.sgml,v 1.32 2002/06/21 03:25:53 momjian Exp $ --> <chapter id="indexes"> <title id="indexes-title">Indexes</title> @@ -181,12 +181,9 @@ CREATE INDEX <replaceable>name</replaceable> ON <replaceable>table</replaceable> </synopsis> <note> <para> - Because of the limited utility of hash indexes, a B-tree index - should generally be preferred over a hash index. We do not have - sufficient evidence that hash indexes are actually faster than - B-trees even for <literal>=</literal> comparisons. Moreover, - hash indexes require coarser locks; see <xref - linkend="locking-indexes">. + Testing has shown that hash indexes are slower than btree indexes, + and the size and build time for hash indexes is much worse. For + these reasons, hash index use is discouraged. </para> </note> </para> diff --git a/doc/src/sgml/ref/create_index.sgml b/doc/src/sgml/ref/create_index.sgml index a3af001006a..6bb972e988e 100644 --- a/doc/src/sgml/ref/create_index.sgml +++ b/doc/src/sgml/ref/create_index.sgml @@ -1,5 +1,5 @@ <!-- -$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_index.sgml,v 1.31 2002/05/18 15:44:47 petere Exp $ +$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_index.sgml,v 1.32 2002/06/21 03:25:53 momjian Exp $ PostgreSQL documentation --> @@ -329,6 +329,11 @@ ERROR: Cannot create index: 'index_name' already exists. an indexed attribute is involved in a comparison using the <literal>=</literal> operator. </para> + <para> + Testing has shown that hash indexes are slower than btree indexes, + and the size and build time for hash indexes is much worse. For + these reasons, hash index use is discouraged. + </para> <para> Currently, only the B-tree and gist access methods support multicolumn diff --git a/doc/src/sgml/xindex.sgml b/doc/src/sgml/xindex.sgml index c6bfb0e19f3..99f069a6748 100644 --- a/doc/src/sgml/xindex.sgml +++ b/doc/src/sgml/xindex.sgml @@ -1,5 +1,5 @@ <!-- -$Header: /cvsroot/pgsql/doc/src/sgml/xindex.sgml,v 1.25 2002/05/29 17:36:40 tgl Exp $ +$Header: /cvsroot/pgsql/doc/src/sgml/xindex.sgml,v 1.26 2002/06/21 03:25:53 momjian Exp $ PostgreSQL documentation --> @@ -11,9 +11,9 @@ PostgreSQL documentation <para> The procedures described thus far let you define new types, new - functions, and new operators. However, we cannot yet define a secondary - index (such as a B-tree, R-tree, or - hash access method) over a new type or its operators. + functions, and new operators. However, we cannot yet define a + secondary index (such as a B-tree, R-tree, or hash access method) + over a new type or its operators. </para> <para> |