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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"
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   command.
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>   B-tree index pages that have become completely empty are reclaimed for
   re-use.  However, there is still a possibility
   of inefficient use of space: if all but a few index keys on a page have
   been deleted, the page remains allocated.  Therefore, a usage
   pattern in which most, but not all, keys in each range are eventually
   deleted will see poor use of space.  For such usage patterns,
   periodic reindexing is recommended.
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>   The potential for bloat in non-B-tree indexes has not been well
   researched.  It is a good idea to periodically monitor the index's physical
   size when using any non-B-tree index type.
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>   Also, for B-tree indexes, a freshly-constructed index is slightly 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 apply to non-B-tree indexes.)  It
   might be worthwhile to reindex periodically just to improve access speed.
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