1#@!#!123s

: / usr / share / doc / postgresql-9.2.24 / html /
Filename : gist-implementation.html
back
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<HTML
><HEAD
><TITLE
>Implementation</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 9.2.24 Documentation"
HREF="index.html"><LINK
REL="UP"
TITLE="GiST Indexes"
HREF="gist.html"><LINK
REL="PREVIOUS"
TITLE="Extensibility"
HREF="gist-extensibility.html"><LINK
REL="NEXT"
TITLE="Examples"
HREF="gist-examples.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="2017-11-06T22:43:11"></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"
><A
HREF="index.html"
>PostgreSQL 9.2.24 Documentation</A
></TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="top"
><A
TITLE="Extensibility"
HREF="gist-extensibility.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="top"
><A
HREF="gist.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="60%"
ALIGN="center"
VALIGN="bottom"
>Chapter 53. GiST Indexes</TD
><TD
WIDTH="20%"
ALIGN="right"
VALIGN="top"
><A
TITLE="Examples"
HREF="gist-examples.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="GIST-IMPLEMENTATION"
>53.3. Implementation</A
></H1
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="GIST-BUFFERING-BUILD"
>53.3.1. GiST buffering build</A
></H2
><P
>   Building large GiST indexes by simply inserting all the tuples tends to be
   slow, because if the index tuples are scattered across the index and the
   index is large enough to not fit in cache, the insertions need to perform
   a lot of random I/O.  Beginning in version 9.2, PostgreSQL supports a more
   efficient method to build GiST indexes based on buffering, which can
   dramatically reduce the number of random I/Os needed for non-ordered data
   sets. For well-ordered data sets the benefit is smaller or non-existent,
   because only a small number of pages receive new tuples at a time, and
   those pages fit in cache even if the index as whole does not.
  </P
><P
>   However, buffering index build needs to call the <CODE
CLASS="FUNCTION"
>penalty</CODE
>
   function more often, which consumes some extra CPU resources. Also, the
   buffers used in the buffering build need temporary disk space, up to
   the size of the resulting index. Buffering can also influence the quality
   of the resulting index, in both positive and negative directions. That
   influence depends on various factors, like the distribution of the input
   data and the operator class implementation.
  </P
><P
>   By default, a GiST index build switches to the buffering method when the
   index size reaches <A
HREF="runtime-config-query.html#GUC-EFFECTIVE-CACHE-SIZE"
>effective_cache_size</A
>. It can
   be manually turned on or off by the <TT
CLASS="LITERAL"
>BUFFERING</TT
> parameter
   to the CREATE INDEX command. The default behavior is good for most cases,
   but turning buffering off might speed up the build somewhat if the input
   data is ordered.
  </P
></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="gist-extensibility.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="gist-examples.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Extensibility</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="gist.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>Examples</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>