Commitebe4375

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Document problems with hash indexes compared to btree.

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+14

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`@@ -1,4 +1,4 @@`
`1`		`-<!-- $Header: /cvsroot/pgsql/doc/src/sgml/indices.sgml,v 1.31 2002/01/07 02:29:12 petere Exp $ -->`
	`1`	`+<!-- $Header: /cvsroot/pgsql/doc/src/sgml/indices.sgml,v 1.32 2002/06/21 03:25:53 momjian Exp $ -->`
`2`	`2`
`3`	`3`	`<chapter id="indexes">`
`4`	`4`	`<title id="indexes-title">Indexes</title>`
`@@ -181,12 +181,9 @@ CREATE INDEX <replaceable>name</replaceable> ON <replaceable>table</replaceable>`
`181`	`181`	`</synopsis>`
`182`	`182`	`<note>`
`183`	`183`	`<para>`
`184`		`- Because of the limited utility of hash indexes, a B-tree index`
`185`		`- should generally be preferred over a hash index. We do not have`
`186`		`- sufficient evidence that hash indexes are actually faster than`
`187`		`- B-trees even for <literal>=</literal> comparisons. Moreover,`
`188`		`- hash indexes require coarser locks; see <xref`
`189`		`- linkend="locking-indexes">.`
	`184`	`+ Testing has shown that hash indexes are slower than btree indexes,`
	`185`	`+ and the size and build time for hash indexes is much worse. For`
	`186`	`+ these reasons, hash index use is discouraged.`
`190`	`187`	`</para>`
`191`	`188`	`</note>`
`192`	`189`	`</para>`

Lines changed: 6 additions & 1 deletion

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`@@ -1,5 +1,5 @@`
`1`	`1`	`<!--`
`2`		`-$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_index.sgml,v 1.31 2002/05/18 15:44:47 petere Exp $`
	`2`	`+$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_index.sgml,v 1.32 2002/06/21 03:25:53 momjian Exp $`
`3`	`3`	`PostgreSQL documentation`
`4`	`4`	`-->`
`5`	`5`
`@@ -329,6 +329,11 @@ ERROR: Cannot create index: 'index_name' already exists.`
`329`	`329`	`an indexed attribute is involved in a comparison using`
`330`	`330`	`the <literal>=</literal> operator.`
`331`	`331`	`</para>`
	`332`	`+ <para>`
	`333`	`+ Testing has shown that hash indexes are slower than btree indexes,`
	`334`	`+ and the size and build time for hash indexes is much worse. For`
	`335`	`+ these reasons, hash index use is discouraged.`
	`336`	`+ </para>`
`332`	`337`
`333`	`338`	`<para>`
`334`	`339`	`Currently, only the B-tree and gist access methods support multicolumn`

Lines changed: 4 additions & 4 deletions

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`@@ -1,5 +1,5 @@`
`1`	`1`	`<!--`
`2`		`-$Header: /cvsroot/pgsql/doc/src/sgml/xindex.sgml,v 1.25 2002/05/29 17:36:40 tgl Exp $`
	`2`	`+$Header: /cvsroot/pgsql/doc/src/sgml/xindex.sgml,v 1.26 2002/06/21 03:25:53 momjian Exp $`
`3`	`3`	`PostgreSQL documentation`
`4`	`4`	`-->`
`5`	`5`
`@@ -11,9 +11,9 @@ PostgreSQL documentation`
`11`	`11`
`12`	`12`	`<para>`
`13`	`13`	`The procedures described thus far let you define new types, new`
`14`		`- functions, and new operators.However, we cannot yet define a secondary`
`15`		`- index (such as a B-tree, R-tree, or`
`16`		`-hash access method)over a new type or its operators.`
	`14`	`+ functions, and new operators. However, we cannot yet define a`
	`15`	`+secondaryindex (such as a B-tree, R-tree, or hash access method)`
	`16`	`+ over a new type or its operators.`
`17`	`17`	`</para>`
`18`	`18`
`19`	`19`	`<para>`

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