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Commit5698f07

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Doc: update VACUUM FREEZE query conflict guidance.
Commit1de58df, which added page-level freezing, taught VACUUM to reuseeach page's "set-visibility-map" snapshotConflictHorizon for freezing(at least in the vast majority of cases where freezing went ahead).This made VACUUM FREEZE much less prone to generating recovery conflictson standbys; VACUUM FREEZE became only slightly more likely to causerecovery conflicts than an equivalent VACUUM.Update old documentation that specifically warned of the likelihood ofrecovery conflicts from VACUUM FREEZE. Explain the same general issue(the issue of VACUUM generating recovery conflicts even in the absenceof dead row cleanup) using the example of conflicts caused by VISIBLEWAL records.
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‎doc/src/sgml/high-availability.sgml

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@@ -1873,10 +1873,16 @@ synchronous_standby_names = 'ANY 2 (s1, s2, s3)'
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</para>
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<para>
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Experienced users should note that both row version cleanup and row version
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freezing will potentially conflict with standby queries. Running a manual
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<command>VACUUM FREEZE</command> is likely to cause conflicts even on tables with
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no updated or deleted rows.
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Row version cleanup isn't the only potential cause of conflicts with
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standby queries. All index-only scans (including those that run on
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standbys) must use an <acronym>MVCC</acronym> snapshot that
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<quote>agrees</quote> with the visibility map. Conflicts are therefore
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required whenever <command>VACUUM</command> <link
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linkend="vacuum-for-visibility-map">sets a page as all-visible in the
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visibility map</link> containing one or more rows
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<emphasis>not</emphasis> visible to all standby queries. So even running
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<command>VACUUM</command> against a table with no updated or deleted rows
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requiring cleanup might lead to conflicts.
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</para>
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<para>

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