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Diffstat (limited to 'doc/src/sgml/gin.sgml')
| -rw-r--r-- | doc/src/sgml/gin.sgml | 37 |
1 files changed, 19 insertions, 18 deletions
diff --git a/doc/src/sgml/gin.sgml b/doc/src/sgml/gin.sgml index 0e9365cce27..6b382230fd0 100644 --- a/doc/src/sgml/gin.sgml +++ b/doc/src/sgml/gin.sgml @@ -1,4 +1,4 @@ -<!-- $PostgreSQL: pgsql/doc/src/sgml/gin.sgml,v 2.3 2006/09/14 21:15:07 tgl Exp $ --> +<!-- $PostgreSQL: pgsql/doc/src/sgml/gin.sgml,v 2.4 2006/09/18 12:11:36 teodor Exp $ --> <chapter id="GIN"> <title>GIN Indexes</title> @@ -14,7 +14,7 @@ <para> <acronym>GIN</acronym> stands for Generalized Inverted Index. It is an index structure storing a set of (key, posting list) pairs, where - 'posting list' is a set of rows in which the key occurs. The + 'posting list' is a set of rows in which the key occurs. Each row may contain many keys. </para> @@ -104,7 +104,8 @@ <listitem> <para> Returns an array of keys of the query to be executed. n contains - strategy number of operation (see <xref linkend="xindex-strategies">). + the strategy number of the operation + (see <xref linkend="xindex-strategies">). Depending on n, query may be different type. </para> </listitem> @@ -114,9 +115,9 @@ <term>bool consistent( bool check[], StrategyNumber n, Datum query)</term> <listitem> <para> - Returns TRUE if indexed value satisfies query qualifier with strategy n - (or may satisfy in case of RECHECK mark in operator class). - Each element of the check array is TRUE if indexed value has a + Returns TRUE if the indexed value satisfies the query qualifier with + strategy n (or may satisfy in case of RECHECK mark in operator class). + Each element of the check array is TRUE if the indexed value has a corresponding key in the query: if (check[i] == TRUE ) the i-th key of the query is present in the indexed value. </para> @@ -135,10 +136,10 @@ <term>Create vs insert</term> <listitem> <para> - In most cases, insertion into <acronym>GIN</acronym> index is slow because - many GIN keys may be inserted for each table row. So, when loading data - in bulk it may be useful to drop index and recreate it - after the data is loaded in the table. + In most cases, insertion into <acronym>GIN</acronym> index is slow + due to the likelihood of many keys being inserted for each value. + So, for bulk insertions into a table it is advisable to to drop the GIN + index and recreate it after finishing bulk insertion. </para> </listitem> </varlistentry> @@ -147,7 +148,7 @@ <term>gin_fuzzy_search_limit</term> <listitem> <para> - The primary goal of development <acronym>GIN</acronym> indices was + The primary goal of developing <acronym>GIN</acronym> indices was support for highly scalable, full-text search in <productname>PostgreSQL</productname> and there are often situations when a full-text search returns a very large set of results. Since reading @@ -158,7 +159,7 @@ <para> Such queries usually contain very frequent words, so the results are not very helpful. To facilitate execution of such queries - <acronym>GIN</acronym> has a configurable soft upper limit of the size + <acronym>GIN</acronym> has a configurable soft upper limit of the size of the returned set, determined by the <varname>gin_fuzzy_search_limit</varname> GUC variable. It is set to 0 by default (no limit). @@ -182,16 +183,16 @@ <title>Limitations</title> <para> - <acronym>GIN</acronym> doesn't support full scan of index due to it's - extremely inefficiency: because of a lot of keys per value, + <acronym>GIN</acronym> doesn't support full index scans due to their + extremely inefficiency: because there are often many keys per value, each heap pointer will returned several times. </para> <para> - When extractQuery returns zero number of keys, <acronym>GIN</acronym> will - emit a error: for different opclass and strategy semantic meaning of void - query may be different (for example, any array contains void array, - but they aren't overlapped with void one), and <acronym>GIN</acronym> can't + When extractQuery returns zero keys, <acronym>GIN</acronym> will emit a + error: for different opclasses and strategies the semantic meaning of a void + query may be different (for example, any array contains the void array, + but they don't overlap the void array), and <acronym>GIN</acronym> can't suggest reasonable answer. </para> |