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During pg_upgrade, conditionally skip transfer of FSMs.

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If a heap on the old cluster has 4 pages or fewer, and the old cluster
was PG v11 or earlier, don't copy or link the FSM. This will shrink
space usage for installations with large numbers of small tables.

This will allow pg_upgrade to take advantage of commit b0eaa4c51b where
we have avoided creation of the free space map for small heap relations.

Author: John Naylor
Reviewed-by: Amit Kapila
Discussion: https://postgr.es/m/CACPNZCu4cOdm3uGnNEGXivy7Gz8UWyQjynDpdkPGabQ18_zK6g%40mail.gmail.com
This commit is contained in:
Amit Kapila
2019-03-15 08:25:57 +05:30
parent 2fadf24e24
commit 13e8643bfc
4 changed files with 89 additions and 3 deletions
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7
doc/src/sgml/ref/pgupgrade.sgml
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@ -792,6 +792,13 @@ psql --username=postgres --file=script.sql postgres
is down.
</para>
<para>
In <productname>PostgreSQL</productname> 12 and later small tables by
default don't have a free space map, as a space optimization. If you are
upgrading a pre-12 cluster, the free space maps of small tables will
likewise not be transferred to the new cluster.
</para>
</refsect1>
<refsect1>