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From: Justin Pryzby <pryzby@telsasoft.com>
To: Tomas Vondra <tomas.vondra@enterprisedb.com>
Cc: Dean Rasheed <dean.a.rasheed@gmail.com>
Cc: pgsql-hackers@postgresql.org
Subject: Re: PoC/WIP: Extended statistics on expressions
Date: Thu, 22 Apr 2021 21:50:12 -0500
Message-ID: <20210423025012.GI7256@telsasoft.com> (raw)
In-Reply-To: <078de413-8e4e-343e-fac1-eb61fd389925@enterprisedb.com>
References: <CAEZATCWYCY=2yEyxa6BwimCPQ_RZHy5GOb6U6i6dGHGQdjQESQ@mail.gmail.com>
	<e4556e47-940d-58a6-73fd-16c5815dd2cd@enterprisedb.com>
	<CAEZATCW2WHfsrbDLzwMvD+kOsBemLhvKwoHGhzR7STtac74XTg@mail.gmail.com>
	<a7d17aec-234d-c7f2-bfdc-99c87767a507@enterprisedb.com>
	<1ed534fb-b42b-f008-35ee-4eb930b0088f@enterprisedb.com>
	<CAEZATCV-JgFzb6aCJxApXg302u4vw+ajj702RHaBVkS_4JPVRg@mail.gmail.com>
	<2cb8a7cd-664f-8681-6ce9-790a50e3c78f@enterprisedb.com>
	<CAEZATCXsfFcXW_A1XCd5QK6zT2M_V+P3aPSktjibHHPzoV+Y-A@mail.gmail.com>
	<096d26e1-f053-a039-047d-a050dbb80ac6@enterprisedb.com>
	<078de413-8e4e-343e-fac1-eb61fd389925@enterprisedb.com>

I suggest to add some kind of reference to stats expressions here.

--- a/doc/src/sgml/maintenance.sgml
+++ b/doc/src/sgml/maintenance.sgml

  <sect2 id="vacuum-for-statistics">
   <title>Updating Planner Statistics</title>

   <indexterm zone="vacuum-for-statistics">
    <primary>statistics</primary>
    <secondary>of the planner</secondary>
   </indexterm>

[...]

@@ -330,10 +330,12 @@
 
     <para>
      Also, by default there is limited information available about
-     the selectivity of functions.  However, if you create an expression
+     the selectivity of functions.  However, if you create a statistics
+     expression or an expression
      index that uses a function call, useful statistics will be
      gathered about the function, which can greatly improve query
      plans that use the expression index.


-- 
Justin





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