Trigger more frequent autovacuums with relallfrozen

Calculate the insert threshold for triggering an autovacuum of a
relation based on the number of unfrozen pages.

By only considering the unfrozen portion of the table when calculating
how many tuples to add to the insert threshold, we can trigger more
frequent vacuums of insert-heavy tables. This increases the chances of
vacuuming those pages when they still reside in shared buffers

This also increases the number of autovacuums triggered by tuples
inserted and not by wraparound risk. We prefer to freeze these pages
during insert-triggered autovacuums, as anti-wraparound vacuums are not
automatically canceled by conflicting lock requests.

We calculate the unfrozen percentage of the table using the recently
added (99f8f3fbbc8f) relallfrozen column of pg_class.

Author: Melanie Plageman <melanieplageman@gmail.com>
Reviewed-by: Nathan Bossart <nathandbossart@gmail.com>
Reviewed-by: Greg Sabino Mullane <htamfids@gmail.com>
Reviewed-by: Robert Treat <rob@xzilla.net>
Reviewed-by: wenhui qiu <qiuwenhuifx@gmail.com>
Discussion: https://postgr.es/m/flat/CAAKRu_aj-P7YyBz_cPNwztz6ohP%2BvWis%3Diz3YcomkB3NpYA--w%40mail.gmail.com

doc/src/sgml/catalogs.sgml

@@ -2072,9 +2072,10 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
       </para>
       <para>
        Number of pages that are marked all-frozen in the table's visibility
-       map.  This is only an estimate and can be used along with
+       map.  This is only an estimate used for triggering autovacuums. It can
-       <structfield>relallvisible</structfield> for scheduling vacuums and
+       also be used along with <structfield>relallvisible</structfield> for
-       tuning <link linkend="runtime-config-vacuum-freezing">vacuum's freezing
+       scheduling manual vacuums and tuning <link
+       linkend="runtime-config-vacuum-freezing">vacuum's freezing
        behavior</link>.
 
        It is updated by

doc/src/sgml/config.sgml

@@ -8773,14 +8773,13 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
        </term>
        <listitem>
         <para>
-         Specifies a fraction of the table size to add to
+         Specifies a fraction of the unfrozen pages in the table to add to
-         <varname>autovacuum_vacuum_insert_threshold</varname>
+         <varname>autovacuum_vacuum_insert_threshold</varname> when deciding
-         when deciding whether to trigger a <command>VACUUM</command>.
+         whether to trigger a <command>VACUUM</command>. The default is
-         The default is <literal>0.2</literal> (20% of table size).
+         <literal>0.2</literal> (20% of unfrozen pages in table). This
-         This parameter can only be set in the <filename>postgresql.conf</filename>
+         parameter can only be set in the <filename>postgresql.conf</filename>
-         file or on the server command line;
+         file or on the server command line; but the setting can be overridden
-         but the setting can be overridden for individual tables by
+         for individual tables by changing table storage parameters.
-         changing table storage parameters.
         </para>
        </listitem>
       </varlistentry>

src/backend/postmaster/autovacuum.c

@@ -2938,7 +2938,6 @@ relation_needs_vacanalyze(Oid relid,
 {
 	bool		force_vacuum;
 	bool		av_enabled;
-	float4		reltuples;		/* pg_class.reltuples */
 
 	/* constants from reloptions or GUC variables */
 	int			vac_base_thresh,
@@ -3052,7 +3051,11 @@ relation_needs_vacanalyze(Oid relid,
 	 */
 	if (PointerIsValid(tabentry) && AutoVacuumingActive())
 	{
-		reltuples = classForm->reltuples;
+		float4		pcnt_unfrozen = 1;
+		float4		reltuples = classForm->reltuples;
+		int32		relpages = classForm->relpages;
+		int32		relallfrozen = classForm->relallfrozen;
+
 		vactuples = tabentry->dead_tuples;
 		instuples = tabentry->ins_since_vacuum;
 		anltuples = tabentry->mod_since_analyze;
@@ -3061,11 +3064,29 @@ relation_needs_vacanalyze(Oid relid,
 		if (reltuples < 0)
 			reltuples = 0;
 
+		/*
+		 * If we have data for relallfrozen, calculate the unfrozen percentage
+		 * of the table to modify insert scale factor. This helps us decide
+		 * whether or not to vacuum an insert-heavy table based on the number
+		 * of inserts to the more "active" part of the table.
+		 */
+		if (relpages > 0 && relallfrozen > 0)
+		{
+			/*
+			 * It could be the stats were updated manually and relallfrozen >
+			 * relpages. Clamp relallfrozen to relpages to avoid nonsensical
+			 * calculations.
+			 */
+			relallfrozen = Min(relallfrozen, relpages);
+			pcnt_unfrozen = 1 - ((float4) relallfrozen / relpages);
+		}
+
 		vacthresh = (float4) vac_base_thresh + vac_scale_factor * reltuples;
 		if (vac_max_thresh >= 0 && vacthresh > (float4) vac_max_thresh)
 			vacthresh = (float4) vac_max_thresh;
 
-		vacinsthresh = (float4) vac_ins_base_thresh + vac_ins_scale_factor * reltuples;
+		vacinsthresh = (float4) vac_ins_base_thresh +
+			vac_ins_scale_factor * reltuples * pcnt_unfrozen;
 		anlthresh = (float4) anl_base_thresh + anl_scale_factor * reltuples;
 
 		/*

src/backend/utils/misc/postgresql.conf.sample

@@ -675,8 +675,8 @@ autovacuum_worker_slots = 16	# autovacuum worker slots to allocate
 #autovacuum_analyze_threshold = 50	# min number of row updates before
 					# analyze
 #autovacuum_vacuum_scale_factor = 0.2	# fraction of table size before vacuum
-#autovacuum_vacuum_insert_scale_factor = 0.2	# fraction of inserts over table
+#autovacuum_vacuum_insert_scale_factor = 0.2	# fraction of unfrozen pages
-						# size before insert vacuum
+          # before insert vacuum
 #autovacuum_analyze_scale_factor = 0.1	# fraction of table size before analyze
 #autovacuum_vacuum_max_threshold = 100000000    # max number of row updates
 						# before vacuum; -1 disables max