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- <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>66.5. GIN Tips and Tricks</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="prev" href="gin-implementation.html" title="66.4. Implementation" /><link rel="next" href="gin-limit.html" title="66.6. Limitations" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">66.5. GIN Tips and Tricks</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="gin-implementation.html" title="66.4. Implementation">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="gin.html" title="Chapter 66. GIN Indexes">Up</a></td><th width="60%" align="center">Chapter 66. GIN Indexes</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="gin-limit.html" title="66.6. Limitations">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="GIN-TIPS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">66.5. GIN Tips and Tricks</h2></div></div></div><div class="variablelist"><dl class="variablelist"><dt><span class="term">Create vs. insert</span></dt><dd><p>
- Insertion into a <acronym class="acronym">GIN</acronym> index can be slow
- due to the likelihood of many keys being inserted for each item.
- So, for bulk insertions into a table it is advisable to drop the GIN
- index and recreate it after finishing bulk insertion.
- </p><p>
- As of <span class="productname">PostgreSQL</span> 8.4, this advice is less
- necessary since delayed indexing is used (see <a class="xref" href="gin-implementation.html#GIN-FAST-UPDATE" title="66.4.1. GIN Fast Update Technique">Section 66.4.1</a> for details). But for very large updates
- it may still be best to drop and recreate the index.
- </p></dd><dt><span class="term"><a class="xref" href="runtime-config-resource.html#GUC-MAINTENANCE-WORK-MEM">maintenance_work_mem</a></span></dt><dd><p>
- Build time for a <acronym class="acronym">GIN</acronym> index is very sensitive to
- the <code class="varname">maintenance_work_mem</code> setting; it doesn't pay to
- skimp on work memory during index creation.
- </p></dd><dt><span class="term"><a class="xref" href="runtime-config-client.html#GUC-GIN-PENDING-LIST-LIMIT">gin_pending_list_limit</a></span></dt><dd><p>
- During a series of insertions into an existing <acronym class="acronym">GIN</acronym>
- index that has <code class="literal">fastupdate</code> enabled, the system will clean up
- the pending-entry list whenever the list grows larger than
- <code class="varname">gin_pending_list_limit</code>. To avoid fluctuations in observed
- response time, it's desirable to have pending-list cleanup occur in the
- background (i.e., via autovacuum). Foreground cleanup operations
- can be avoided by increasing <code class="varname">gin_pending_list_limit</code>
- or making autovacuum more aggressive.
- However, enlarging the threshold of the cleanup operation means that
- if a foreground cleanup does occur, it will take even longer.
- </p><p>
- <code class="varname">gin_pending_list_limit</code> can be overridden for individual
- GIN indexes by changing storage parameters, and which allows each
- GIN index to have its own cleanup threshold.
- For example, it's possible to increase the threshold only for the GIN
- index which can be updated heavily, and decrease it otherwise.
- </p></dd><dt><span class="term"><a class="xref" href="runtime-config-client.html#GUC-GIN-FUZZY-SEARCH-LIMIT">gin_fuzzy_search_limit</a></span></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
- <code class="varname">gin_fuzzy_search_limit</code> 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">“<span class="quote">Soft</span>”</span> means that the actual number of returned results
- could differ somewhat from the specified limit, depending on the query
- and the quality of the system's random number generator.
- </p><p>
- From experience, values in the thousands (e.g., 5000 — 20000)
- work well.
- </p></dd></dl></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="gin-implementation.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="gin.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="gin-limit.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">66.4. Implementation </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 66.6. Limitations</td></tr></table></div></body></html>
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