Will just park the idea for the documentation here. If
you feel this should be in a follow-up patch, I am ok
with that and will follow-up on it afterwards.
+++ b/doc/src/sgml/maintenance.sgml
@@ -905,6 +905,12 @@ vacuum threshold = Minimum(vacuum max threshold,
vacuum base threshold + vacuum
<xref linkend="guc-autovacuum-vacuum-scale-factor"/>,
and the number of tuples is
<structname>pg_class</structname>.<structfield>reltuples</structfield>.
+ With the default values of <xref
linkend="autovacuum_vacuum_scale_factor"/> and
+ <xref linkend="autovacuum_vacuum_threshold"/>, the <quote>vacuum
threshold</quote> increases as
+ the number of tuples in the table increases; and this reduces the
table's eligibility for
+ <command>VACUUM</command>. Therefore,
+ <xref linkend="autovacuum_vacuum_max_threshold"/> provides a cap
on the number of obsolete rows
+ before the table becomes eligible for a vacuum.
</para>
Regards,
Sami
