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From: Nathan Bossart <[email protected]>
Subject: [PATCH v2 1/2] Further adjust guidance for running vacuumdb after pg_upgrade.
Date: Wed, 23 Apr 2025 10:11:46 -0500

Since pg_upgrade does not transfer the cumulative statistics used
for triggering autovacuum and autoanalyze, the server may take much
longer than expected to process them post-upgrade.  Currently, the
pg_upgrade documentation recommends analyzing only relations for
which optimizer statistics were not carried over during upgrade.
This commit appends another recommendation to also analyze all
relations to update the relevant cumulative statistics, similar to
the recommendation for pg_stat_reset().

Reported-by: Christoph Berg <[email protected]>
Reviewed-by: Christoph Berg <[email protected]>
Discussion: https://postgr.es/m/aAfxfKC82B9NvJDj%40msg.df7cb.de
---
 doc/src/sgml/ref/pgupgrade.sgml | 12 +++++++-----
 src/bin/pg_upgrade/check.c      |  9 ++++++---
 2 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/doc/src/sgml/ref/pgupgrade.sgml b/doc/src/sgml/ref/pgupgrade.sgml
index df13365b287..648c6e2967c 100644
--- a/doc/src/sgml/ref/pgupgrade.sgml
+++ b/doc/src/sgml/ref/pgupgrade.sgml
@@ -833,17 +833,19 @@ psql --username=postgres --file=script.sql postgres
 
     <para>
      Because not all statistics are not transferred by
-     <command>pg_upgrade</command>, you will be instructed to run a command to
+     <command>pg_upgrade</command>, you will be instructed to run commands to
      regenerate that information at the end of the upgrade.  You might need to
      set connection parameters to match your new cluster.
     </para>
 
     <para>
-     Using <command>vacuumdb --all --analyze-only --missing-stats-only</command>
-     can efficiently generate such statistics.  Alternatively,
+     First, use
      <command>vacuumdb --all --analyze-in-stages --missing-stats-only</command>
-     can be used to generate minimal statistics quickly.  For either command,
-     the use of <option>--jobs</option> can speed it up.
+     to quickly generate minimal optimizer statistics for relations without
+     any.  Then, use <command>vacuumdb --all --analyze-only</command> to ensure
+     all relations have updated cumulative statistics for triggering vacuum and
+     analyze.  For both commands, the use of <option>--jobs</option> can speed
+     it up.
      If <varname>vacuum_cost_delay</varname> is set to a non-zero
      value, this can be overridden to speed up statistics generation
      using <envar>PGOPTIONS</envar>, e.g., <literal>PGOPTIONS='-c
diff --git a/src/bin/pg_upgrade/check.c b/src/bin/pg_upgrade/check.c
index 18c2d652bb6..940fc77fc2e 100644
--- a/src/bin/pg_upgrade/check.c
+++ b/src/bin/pg_upgrade/check.c
@@ -814,9 +814,12 @@ output_completion_banner(char *deletion_script_file_name)
 	}
 
 	pg_log(PG_REPORT,
-		   "Some optimizer statistics may not have been transferred by pg_upgrade.\n"
-		   "Once you start the new server, consider running:\n"
-		   "    %s/vacuumdb %s--all --analyze-in-stages --missing-stats-only", new_cluster.bindir, user_specification.data);
+		   "Some statistics are not transferred by pg_upgrade.\n"
+		   "Once you start the new server, consider running these two commands:\n"
+		   "    %s/vacuumdb %s--all --analyze-in-stages --missing-stats-only\n"
+		   "    %s/vacuumdb %s--all --analyze-only",
+		   new_cluster.bindir, user_specification.data,
+		   new_cluster.bindir, user_specification.data);
 
 	if (deletion_script_file_name)
 		pg_log(PG_REPORT,
-- 
2.39.5 (Apple Git-154)


--Yk+v15XI0xqDWTQr
Content-Type: text/plain; charset=us-ascii
Content-Disposition: attachment;
	filename="v2-0002-vacuumdb-Don-t-skip-empty-relations-in-missing-st.patch"

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