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doc: improve text around consistency of statistics values 

Discussion: https://postgr.es/m/CAKFQuwZ4CXtTyR19vFbd9WwmW-4BvgAenmF2CfUpx0LWwRPGYg@mail.gmail.com

Author: David G. Johnston

Backpatch-through: master
This commit is contained in:
Bruce Momjian 2023-10-27 21:24:55 -04:00
parent eb544d7fd9
commit 05ce730978
1 changed files with 3 additions and 4 deletions
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7
doc/src/sgml/maintenance.sgml
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@ -924,10 +924,9 @@ vacuum insert threshold = vacuum base insert threshold + vacuum insert scale fac
<xref linkend="reloption-autovacuum-freeze-min-age"/> as this may allow
tuples to be frozen by earlier vacuums. The number of obsolete tuples and
the number of inserted tuples are obtained from the cumulative statistics system;
it is a semi-accurate count updated by each <command>UPDATE</command>,
<command>DELETE</command> and <command>INSERT</command> operation. (It is
only semi-accurate because some information might be lost under heavy
load.) If the <structfield>relfrozenxid</structfield> value of the table
it is an eventually-consistent count updated by each <command>UPDATE</command>,
<command>DELETE</command> and <command>INSERT</command> operation.
If the <structfield>relfrozenxid</structfield> value of the table
is more than <varname>vacuum_freeze_table_age</varname> transactions old,
an aggressive vacuum is performed to freeze old tuples and advance
<structfield>relfrozenxid</structfield>; otherwise, only pages that have been modified