Sophie: postgresql8.4-docs-8.4.12-0.1mdv2010.2 i586

postgresql8.4-docs-8.4.12-0.1mdv2010.2.i586.rpm

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>23.2. Routine Reindexing</A
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>   In some situations it is worthwhile to rebuild indexes periodically
   with the <A
HREF="sql-reindex.html"
><I
>REINDEX</I
></A
>
   command.
  </P
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>   In <SPAN
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>PostgreSQL</SPAN
> releases before 7.4, periodic reindexing
   was frequently necessary to avoid <SPAN
CLASS="QUOTE"
>"index bloat"</SPAN
>, due to lack of
   internal space reclamation in B-tree indexes.  Any situation in which the
   range of index keys changed over time &mdash; for example, an index on
   timestamps in a table where old entries are eventually deleted &mdash;
   would result in bloat, because index pages for no-longer-needed portions
   of the key range were not reclaimed for re-use.  Over time, the index size
   could become indefinitely much larger than the amount of useful data in it.
  </P
><P
>   In <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> 7.4 and later, index pages that have become
   completely empty are reclaimed for re-use.  There is still a possibility
   for inefficient use of space: if all but a few index keys on a page have
   been deleted, the page remains allocated.  So a usage pattern in which all
   but a few keys in each range are eventually deleted will see poor use of
   space.  For such usage patterns, periodic reindexing is recommended.
  </P
><P
>   The potential for bloat in non-B-tree indexes has not been well
   characterized.  It is a good idea to keep an eye on the index's physical
   size when using any non-B-tree index type.
  </P
><P
>   Also, for B-tree indexes a freshly-constructed index is somewhat faster to
   access than one that has been updated many times, because logically
   adjacent pages are usually also physically adjacent in a newly built index.
   (This consideration does not currently apply to non-B-tree indexes.)  It
   might be worthwhile to reindex periodically just to improve access speed.
  </P
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