Sophie: postgresql8.3-docs-8.3.6-2mdv2008.1 x86

postgresql8.3-docs-8.3.6-2mdv2008.1.x86_64.rpm

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<HTML
><HEAD
><TITLE
>GIN tips and tricks</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK
REV="MADE"
HREF="mailto:pgsql-docs@postgresql.org"><LINK
REL="HOME"
TITLE="PostgreSQL 8.3.6 Documentation"
HREF="index.html"><LINK
REL="UP"
TITLE="GIN Indexes"
HREF="gin.html"><LINK
REL="PREVIOUS"
TITLE="Implementation"
HREF="gin-implementation.html"><LINK
REL="NEXT"
TITLE="Limitations"
HREF="gin-limit.html"><LINK
REL="STYLESHEET"
TYPE="text/css"
HREF="stylesheet.css"><META
HTTP-EQUIV="Content-Type"
CONTENT="text/html; charset=ISO-8859-1"><META
NAME="creation"
CONTENT="2009-02-03T04:34:16"></HEAD
><BODY
CLASS="SECT1"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="5"
ALIGN="center"
VALIGN="bottom"
>PostgreSQL 8.3.6 Documentation</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="top"
><A
HREF="gin-implementation.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="top"
><A
HREF="gin.html"
>Fast Backward</A
></TD
><TD
WIDTH="60%"
ALIGN="center"
VALIGN="bottom"
>Chapter 52. GIN Indexes</TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="top"
><A
HREF="gin.html"
>Fast Forward</A
></TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="top"
><A
HREF="gin-limit.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="GIN-TIPS"
>52.4. GIN tips and tricks</A
></H1
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
>Create vs insert</DT
><DD
><P
>     In most cases, insertion into a <ACRONYM
CLASS="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 drop the GIN
     index and recreate it after finishing bulk insertion.
    </P
></DD
><DT
><A
HREF="runtime-config-resource.html#GUC-MAINTENANCE-WORK-MEM"
>maintenance_work_mem</A
></DT
><DD
><P
>     Build time for a <ACRONYM
CLASS="ACRONYM"
>GIN</ACRONYM
> index is very sensitive to
     the <TT
CLASS="VARNAME"
>maintenance_work_mem</TT
> setting; it doesn't pay to
     skimp on work memory during index creation.
    </P
></DD
><DT
><A
HREF="runtime-config-client.html#GUC-GIN-FUZZY-SEARCH-LIMIT"
>gin_fuzzy_search_limit</A
></DT
><DD
><P
>     The primary goal of developing <ACRONYM
CLASS="ACRONYM"
>GIN</ACRONYM
> indexes was
     to create support for highly scalable, full-text search in
     <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>, and there are often situations when
     a full-text search returns a very large set of results.  Moreover, this
     often happens when the query contains very frequent words, so that the
     large result set is not even useful.  Since reading many
     tuples from the disk and sorting them could take a lot of time, this is
     unacceptable for production.  (Note that the index search itself is very
     fast.)
    </P
><P
>     To facilitate controlled execution of such queries
     <ACRONYM
CLASS="ACRONYM"
>GIN</ACRONYM
> has a configurable soft upper limit on the
     number of rows returned, the
     <TT
CLASS="VARNAME"
>gin_fuzzy_search_limit</TT
> configuration parameter.
     It is set to 0 (meaning no limit) by default.
     If a non-zero limit is set, then the returned set is a subset of
     the whole result set, chosen at random.
    </P
><P
>     <SPAN
CLASS="QUOTE"
>"Soft"</SPAN
> means that the actual number of returned results
     could differ slightly from the specified limit, depending on the query
     and the quality of the system's random number generator.
    </P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="gin-implementation.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="index.html"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="gin-limit.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Implementation</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="gin.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>Limitations</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>