Add VACUUM/ANALYZE BUFFER_USAGE_LIMIT option

Add new options to the VACUUM and ANALYZE commands called
BUFFER_USAGE_LIMIT to allow users more control over how large to make the
buffer access strategy that is used to limit the usage of buffers in
shared buffers.  Larger rings can allow VACUUM to run more quickly but
have the drawback of VACUUM possibly evicting more buffers from shared
buffers that might be useful for other queries running on the database.

Here we also add a new GUC named vacuum_buffer_usage_limit which controls
how large to make the access strategy when it's not specified in the
VACUUM/ANALYZE command.  This defaults to 256KB, which is the same size as
the access strategy was prior to this change.  This setting also
controls how large to make the buffer access strategy for autovacuum.

Per idea by Andres Freund.

Author: Melanie Plageman
Reviewed-by: David Rowley
Reviewed-by: Andres Freund
Reviewed-by: Justin Pryzby
Reviewed-by: Bharath Rupireddy
Discussion: https://postgr.es/m/20230111182720.ejifsclfwymw2reb@awork3.anarazel.de

doc/src/sgml/config.sgml

@@ -2001,6 +2001,36 @@ include_dir 'conf.d'
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-vacuum-buffer-usage-limit" xreflabel="vacuum_buffer_usage_limit">
+      <term>
+       <varname>vacuum_buffer_usage_limit</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>vacuum_buffer_usage_limit</varname> configuration parameter</primary>
+       </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Specifies the size of the
+        <glossterm linkend="glossary-buffer-access-strategy">Buffer Access Strategy</glossterm>
+        used by the <command>VACUUM</command> and <command>ANALYZE</command>
+        commands.  A setting of <literal>0</literal> will allow the operation
+        to use any number of <varname>shared_buffers</varname>.  Otherwise
+        valid sizes range from <literal>128 KB</literal> to
+        <literal>16 GB</literal>.  If the specified size would exceed 1/8 the
+        size of <varname>shared_buffers</varname>, the size is silently capped
+        to that value.  The default value is <literal>256 KB</literal>.  If
+        this value is specified without units, it is taken as kilobytes.  This
+        parameter can be set at any time.  It can be overridden for
+        <xref linkend="sql-vacuum"/> and <xref linkend="sql-analyze"/>
+        when passing the <option>BUFFER_USAGE_LIMIT</option> option.  Higher
+        settings can allow <command>VACUUM</command> and
+        <command>ANALYZE</command> to run more quickly, but having too large a
+        setting may cause too many other useful pages to be evicted from
+        shared buffers.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="guc-logical-decoding-work-mem" xreflabel="logical_decoding_work_mem">
       <term><varname>logical_decoding_work_mem</varname> (<type>integer</type>)
       <indexterm>

doc/src/sgml/ref/analyze.sgml

@@ -28,6 +28,7 @@ ANALYZE [ VERBOSE ] [ <replaceable class="parameter">table_and_columns</replacea
 
     VERBOSE [ <replaceable class="parameter">boolean</replaceable> ]
     SKIP_LOCKED [ <replaceable class="parameter">boolean</replaceable> ]
+    BUFFER_USAGE_LIMIT [ <replaceable class="parameter">string</replaceable> ]
 
 <phrase>and <replaceable class="parameter">table_and_columns</replaceable> is:</phrase>
 
@@ -95,6 +96,25 @@ ANALYZE [ VERBOSE ] [ <replaceable class="parameter">table_and_columns</replacea
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term><literal>BUFFER_USAGE_LIMIT</literal></term>
+    <listitem>
+     <para>
+      Specifies the
+      <glossterm linkend="glossary-buffer-access-strategy">Buffer Access Strategy</glossterm>
+      ring buffer size for <command>ANALYZE</command>.  This size is used to
+      calculate the number of shared buffers which will be reused as part of
+      this strategy.  <literal>0</literal> disables use of a
+      <literal>Buffer Access Strategy</literal>.   When this option is not
+      specified, <command>ANALYZE</command> uses the value from
+      <xref linkend="guc-vacuum-buffer-usage-limit"/>.  Higher settings can
+      allow <command>ANALYZE</command> to run more quickly, but having too
+      large a setting may cause too many other useful pages to be evicted from
+      shared buffers.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><replaceable class="parameter">boolean</replaceable></term>
     <listitem>

doc/src/sgml/ref/vacuum.sgml

@@ -39,6 +39,7 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet
     PARALLEL <replaceable class="parameter">integer</replaceable>
     SKIP_DATABASE_STATS [ <replaceable class="parameter">boolean</replaceable> ]
     ONLY_DATABASE_STATS [ <replaceable class="parameter">boolean</replaceable> ]
+    BUFFER_USAGE_LIMIT [ <replaceable class="parameter">string</replaceable> ]
 
 <phrase>and <replaceable class="parameter">table_and_columns</replaceable> is:</phrase>
 
@@ -345,6 +346,29 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term><literal>BUFFER_USAGE_LIMIT</literal></term>
+    <listitem>
+     <para>
+      Specifies the
+      <glossterm linkend="glossary-buffer-access-strategy">Buffer Access Strategy</glossterm>
+      ring buffer size for <command>VACUUM</command>.  This size is used to
+      calculate the number of shared buffers which will be reused as part of
+      this strategy.  <literal>0</literal> disables use of a
+      <literal>Buffer Access Strategy</literal>.  If <option>ANALYZE</option>
+      is also specified, the <option>BUFFER_USAGE_LIMIT</option> value is used
+      for both the vacuum and analyze stages.  This option can't be used with
+      the <option>FULL</option> option except if <option>ANALYZE</option> is
+      also specified.  When this option is not specified,
+      <command>VACUUM</command> uses the value from
+      <xref linkend="guc-vacuum-buffer-usage-limit"/>.  Higher settings can
+      allow <command>VACUUM</command> to run more quickly, but having too
+      large a setting may cause too many other useful pages to be evicted from
+      shared buffers.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><replaceable class="parameter">boolean</replaceable></term>
     <listitem>

src/backend/commands/vacuum.c

@@ -57,6 +57,7 @@
 #include "utils/acl.h"
 #include "utils/fmgroids.h"
 #include "utils/guc.h"
+#include "utils/guc_hooks.h"
 #include "utils/memutils.h"
 #include "utils/pg_rusage.h"
 #include "utils/snapmgr.h"
@@ -120,6 +121,26 @@ static VacOptValue get_vacoptval_from_boolean(DefElem *def);
 static bool vac_tid_reaped(ItemPointer itemptr, void *state);
 static int	vac_cmp_itemptr(const void *left, const void *right);
 
+/*
+ * GUC check function to ensure GUC value specified is within the allowable
+ * range.
+ */
+bool
+check_vacuum_buffer_usage_limit(int *newval, void **extra,
+								GucSource source)
+{
+	/* Value upper and lower hard limits are inclusive */
+	if (*newval == 0 || (*newval >= MIN_BAS_VAC_RING_SIZE_KB &&
+						 *newval <= MAX_BAS_VAC_RING_SIZE_KB))
+		return true;
+
+	/* Value does not fall within any allowable range */
+	GUC_check_errdetail("\"vacuum_buffer_usage_limit\" must be 0 or between %d KB and %d KB",
+						MIN_BAS_VAC_RING_SIZE_KB, MAX_BAS_VAC_RING_SIZE_KB);
+
+	return false;
+}
+
 /*
  * Primary entry point for manual VACUUM and ANALYZE commands
  *
@@ -139,6 +160,7 @@ ExecVacuum(ParseState *pstate, VacuumStmt *vacstmt, bool isTopLevel)
 	bool		disable_page_skipping = false;
 	bool		process_main = true;
 	bool		process_toast = true;
+	int			ring_size;
 	bool		skip_database_stats = false;
 	bool		only_database_stats = false;
 	MemoryContext vac_context;
@@ -151,6 +173,12 @@ ExecVacuum(ParseState *pstate, VacuumStmt *vacstmt, bool isTopLevel)
 	/* By default parallel vacuum is enabled */
 	params.nworkers = 0;
 
+	/*
+	 * Set this to an invalid value so it is clear whether or not a
+	 * BUFFER_USAGE_LIMIT was specified when making the access strategy.
+	 */
+	ring_size = -1;
+
 	/* Parse options list */
 	foreach(lc, vacstmt->options)
 	{
@@ -161,6 +189,48 @@ ExecVacuum(ParseState *pstate, VacuumStmt *vacstmt, bool isTopLevel)
 			verbose = defGetBoolean(opt);
 		else if (strcmp(opt->defname, "skip_locked") == 0)
 			skip_locked = defGetBoolean(opt);
+		else if (strcmp(opt->defname, "buffer_usage_limit") == 0)
+		{
+			const char *hintmsg;
+			int			result;
+			char	   *vac_buffer_size;
+
+			if (opt->arg == NULL)
+			{
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("buffer_usage_limit option requires a valid value"),
+						 parser_errposition(pstate, opt->location)));
+			}
+
+			vac_buffer_size = defGetString(opt);
+
+			if (!parse_int(vac_buffer_size, &result, GUC_UNIT_KB, &hintmsg))
+			{
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+						 errmsg("value: \"%s\": is invalid for buffer_usage_limit",
+								vac_buffer_size),
+						 hintmsg ? errhint("%s", _(hintmsg)) : 0));
+			}
+
+			/*
+			 * Check that the specified size falls within the hard upper and
+			 * lower limits if it is not 0.  We explicitly disallow -1 since
+			 * that behavior can be obtained by not specifying
+			 * BUFFER_USAGE_LIMIT.
+			 */
+			if (result != 0 &&
+				(result < MIN_BAS_VAC_RING_SIZE_KB || result > MAX_BAS_VAC_RING_SIZE_KB))
+			{
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+						 errmsg("buffer_usage_limit option must be 0 or between %d KB and %d KB",
+								MIN_BAS_VAC_RING_SIZE_KB, MAX_BAS_VAC_RING_SIZE_KB)));
+			}
+
+			ring_size = result;
+		}
 		else if (!vacstmt->is_vacuumcmd)
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
@@ -265,6 +335,17 @@ ExecVacuum(ParseState *pstate, VacuumStmt *vacstmt, bool isTopLevel)
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				 errmsg("VACUUM FULL cannot be performed in parallel")));
 
+	/*
+	 * BUFFER_USAGE_LIMIT does nothing for VACUUM (FULL) so just raise an
+	 * ERROR for that case.  VACUUM (FULL, ANALYZE) does make use of it, so
+	 * we'll permit that.
+	 */
+	if (ring_size != -1 && (params.options & VACOPT_FULL) &&
+		!(params.options & VACOPT_ANALYZE))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("BUFFER_USAGE_LIMIT cannot be specified for VACUUM FULL")));
+
 	/*
 	 * Make sure VACOPT_ANALYZE is specified if any column lists are present.
 	 */
@@ -366,7 +447,19 @@ ExecVacuum(ParseState *pstate, VacuumStmt *vacstmt, bool isTopLevel)
 
 		MemoryContext old_context = MemoryContextSwitchTo(vac_context);
 
-		bstrategy = GetAccessStrategy(BAS_VACUUM);
+		Assert(ring_size >= -1);
+
+		/*
+		 * If BUFFER_USAGE_LIMIT was specified by the VACUUM or ANALYZE
+		 * command, it overrides the value of VacuumBufferUsageLimit.  Either
+		 * value may be 0, in which case GetAccessStrategyWithSize() will
+		 * return NULL, effectively allowing full use of shared buffers.
+		 */
+		if (ring_size == -1)
+			ring_size = VacuumBufferUsageLimit;
+
+		bstrategy = GetAccessStrategyWithSize(BAS_VACUUM, ring_size);
+
 		MemoryContextSwitchTo(old_context);
 	}
 

src/backend/commands/vacuumparallel.c

@@ -87,6 +87,12 @@ typedef struct PVShared
 	 */
 	int			maintenance_work_mem_worker;
 
+	/*
+	 * The number of buffers each worker's Buffer Access Strategy ring should
+	 * contain.
+	 */
+	int			ring_nbuffers;
+
 	/*
 	 * Shared vacuum cost balance.  During parallel vacuum,
 	 * VacuumSharedCostBalance points to this value and it accumulates the
@@ -365,6 +371,9 @@ parallel_vacuum_init(Relation rel, Relation *indrels, int nindexes,
 		maintenance_work_mem / Min(parallel_workers, nindexes_mwm) :
 		maintenance_work_mem;
 
+	/* Use the same buffer size for all workers */
+	shared->ring_nbuffers = GetAccessStrategyBufferCount(bstrategy);
+
 	pg_atomic_init_u32(&(shared->cost_balance), 0);
 	pg_atomic_init_u32(&(shared->active_nworkers), 0);
 	pg_atomic_init_u32(&(shared->idx), 0);
@@ -1018,8 +1027,9 @@ parallel_vacuum_main(dsm_segment *seg, shm_toc *toc)
 	pvs.indname = NULL;
 	pvs.status = PARALLEL_INDVAC_STATUS_INITIAL;
 
-	/* Each parallel VACUUM worker gets its own access strategy */
+	/* Each parallel VACUUM worker gets its own access strategy. */
-	pvs.bstrategy = GetAccessStrategy(BAS_VACUUM);
+	pvs.bstrategy = GetAccessStrategyWithSize(BAS_VACUUM,
+											  shared->ring_nbuffers * (BLCKSZ / 1024));
 
 	/* Setup error traceback support for ereport() */
 	errcallback.callback = parallel_vacuum_error_callback;

src/backend/postmaster/autovacuum.c

@@ -2349,11 +2349,21 @@ do_autovacuum(void)
 	}
 
 	/*
-	 * Create a buffer access strategy object for VACUUM to use.  We want to
+	 * Optionally, create a buffer access strategy object for VACUUM to use.
-	 * use the same one across all the vacuum operations we perform, since the
+	 * We use the same BufferAccessStrategy object for all tables VACUUMed by
-	 * point is for VACUUM not to blow out the shared cache.
+	 * this worker to prevent autovacuum from blowing out shared buffers.
+	 *
+	 * VacuumBufferUsageLimit being set to 0 results in
+	 * GetAccessStrategyWithSize returning NULL, effectively meaning we can
+	 * use up to all of shared buffers.
+	 *
+	 * If we later enter failsafe mode on any of the tables being vacuumed, we
+	 * will cease use of the BufferAccessStrategy only for that table.
+	 *
+	 * XXX should we consider adding code to adjust the size of this if
+	 * VacuumBufferUsageLimit changes?
 	 */
-	bstrategy = GetAccessStrategy(BAS_VACUUM);
+	bstrategy = GetAccessStrategyWithSize(BAS_VACUUM, VacuumBufferUsageLimit);
 
 	/*
 	 * create a memory context to act as fake PortalContext, so that the

src/backend/storage/buffer/README

@@ -229,12 +229,12 @@ update hint bits).  In a scan that modifies every page in the scan, like a
 bulk UPDATE or DELETE, the buffers in the ring will always be dirtied and
 the ring strategy effectively degrades to the normal strategy.
 
-VACUUM uses a 256KB ring like sequential scans, but dirty pages are not
+VACUUM uses a ring like sequential scans, however, the size of this ring is
-removed from the ring.  Instead, WAL is flushed if needed to allow reuse of
+controlled by the vacuum_buffer_usage_limit GUC.  Dirty pages are not removed
-the buffers.  Before introducing the buffer ring strategy in 8.3, VACUUM's
+from the ring.  Instead, WAL is flushed if needed to allow reuse of the
-buffers were sent to the freelist, which was effectively a buffer ring of 1
+buffers.  Before introducing the buffer ring strategy in 8.3, VACUUM's buffers
-buffer, resulting in excessive WAL flushing.  Allowing VACUUM to update
+were sent to the freelist, which was effectively a buffer ring of 1 buffer,
-256KB between WAL flushes should be more efficient.
+resulting in excessive WAL flushing.
 
 Bulk writes work similarly to VACUUM.  Currently this applies only to
 COPY IN and CREATE TABLE AS SELECT.  (Might it be interesting to make

src/backend/storage/buffer/freelist.c

@@ -540,8 +540,7 @@ StrategyInitialize(bool init)
 BufferAccessStrategy
 GetAccessStrategy(BufferAccessStrategyType btype)
 {
-	BufferAccessStrategy strategy;
+	int			ring_size_kb;
-	int			nbuffers;
 
 	/*
 	 * Select ring size to use.  See buffer/README for rationales.
@@ -556,13 +555,13 @@ GetAccessStrategy(BufferAccessStrategyType btype)
 			return NULL;
 
 		case BAS_BULKREAD:
-			nbuffers = 256 * 1024 / BLCKSZ;
+			ring_size_kb = 256;
 			break;
 		case BAS_BULKWRITE:
-			nbuffers = 16 * 1024 * 1024 / BLCKSZ;
+			ring_size_kb = 16 * 1024;
 			break;
 		case BAS_VACUUM:
-			nbuffers = 256 * 1024 / BLCKSZ;
+			ring_size_kb = 256;
 			break;
 
 		default:
@@ -571,21 +570,65 @@ GetAccessStrategy(BufferAccessStrategyType btype)
 			return NULL;		/* keep compiler quiet */
 	}
 
-	/* Make sure ring isn't an undue fraction of shared buffers */
+	return GetAccessStrategyWithSize(btype, ring_size_kb);
-	nbuffers = Min(NBuffers / 8, nbuffers);
+}
+
+/*
+ * GetAccessStrategyWithSize -- create a BufferAccessStrategy object with a
+ *		number of buffers equivalent to the passed in size.
+ *
+ * If the given ring size is 0, no BufferAccessStrategy will be created and
+ * the function will return NULL.  ring_size_kb must not be negative.
+ */
+BufferAccessStrategy
+GetAccessStrategyWithSize(BufferAccessStrategyType btype, int ring_size_kb)
+{
+	int			ring_buffers;
+	BufferAccessStrategy strategy;
+
+	Assert(ring_size_kb >= 0);
+
+	/* Figure out how many buffers ring_size_kb is */
+	ring_buffers = ring_size_kb / (BLCKSZ / 1024);
+
+	/* 0 means unlimited, so no BufferAccessStrategy required */
+	if (ring_buffers == 0)
+		return NULL;
+
+	/* Cap to 1/8th of shared_buffers */
+	ring_buffers = Min(NBuffers / 8, ring_buffers);
+
+	/* NBuffers should never be less than 16, so this shouldn't happen */
+	Assert(ring_buffers > 0);
 
 	/* Allocate the object and initialize all elements to zeroes */
 	strategy = (BufferAccessStrategy)
 		palloc0(offsetof(BufferAccessStrategyData, buffers) +
-				nbuffers * sizeof(Buffer));
+				ring_buffers * sizeof(Buffer));
 
 	/* Set fields that don't start out zero */
 	strategy->btype = btype;
-	strategy->nbuffers = nbuffers;
+	strategy->nbuffers = ring_buffers;
 
 	return strategy;
 }
 
+/*
+ * GetAccessStrategyBufferCount -- an accessor for the number of buffers in
+ *		the ring
+ *
+ * Returns 0 on NULL input to match behavior of GetAccessStrategyWithSize()
+ * returning NULL with 0 size.
+ */
+int
+GetAccessStrategyBufferCount(BufferAccessStrategy strategy)
+{
+	if (strategy == NULL)
+		return 0;
+
+	return strategy->nbuffers;
+}
+
 /*
  * FreeAccessStrategy -- release a BufferAccessStrategy object
  *

src/backend/utils/init/globals.c

@@ -139,7 +139,10 @@ int			max_worker_processes = 8;
 int			max_parallel_workers = 8;
 int			MaxBackends = 0;
 
-int			VacuumCostPageHit = 1;	/* GUC parameters for vacuum */
+/* GUC parameters for vacuum */
+int			VacuumBufferUsageLimit = 256;
+
+int			VacuumCostPageHit = 1;
 int			VacuumCostPageMiss = 2;
 int			VacuumCostPageDirty = 20;
 int			VacuumCostLimit = 200;

src/backend/utils/misc/guc_tables.c

@@ -2224,6 +2224,17 @@ struct config_int ConfigureNamesInt[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"vacuum_buffer_usage_limit", PGC_USERSET, RESOURCES_MEM,
+			gettext_noop("Sets the buffer pool size for VACUUM, ANALYZE, and autovacuum."),
+			NULL,
+			GUC_UNIT_KB
+		},
+		&VacuumBufferUsageLimit,
+		256, 0, MAX_BAS_VAC_RING_SIZE_KB,
+		check_vacuum_buffer_usage_limit, NULL, NULL
+	},
+
 	{
 		{"shared_memory_size", PGC_INTERNAL, PRESET_OPTIONS,
 			gettext_noop("Shows the size of the server's main shared memory area (rounded up to the nearest MB)."),

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

@@ -157,6 +157,9 @@
 					#   mmap
 					# (change requires restart)
 #min_dynamic_shared_memory = 0MB	# (change requires restart)
+#vacuum_buffer_usage_limit = 256 # size of vacuum and analyze buffer access strategy ring.
+				 # 0 to disable vacuum buffer access strategy
+				 # range 128kB to 16GB
 
 # - Disk -
 

src/bin/psql/tab-complete.c

@@ -2662,7 +2662,7 @@ psql_completion(const char *text, int start, int end)
 		 * one word, so the above test is correct.
 		 */
 		if (ends_with(prev_wd, '(') || ends_with(prev_wd, ','))
-			COMPLETE_WITH("VERBOSE", "SKIP_LOCKED");
+			COMPLETE_WITH("VERBOSE", "SKIP_LOCKED", "BUFFER_USAGE_LIMIT");
 		else if (TailMatches("VERBOSE|SKIP_LOCKED"))
 			COMPLETE_WITH("ON", "OFF");
 	}
@@ -4620,7 +4620,7 @@ psql_completion(const char *text, int start, int end)
 						  "DISABLE_PAGE_SKIPPING", "SKIP_LOCKED",
 						  "INDEX_CLEANUP", "PROCESS_MAIN", "PROCESS_TOAST",
 						  "TRUNCATE", "PARALLEL", "SKIP_DATABASE_STATS",
-						  "ONLY_DATABASE_STATS");
+						  "ONLY_DATABASE_STATS", "BUFFER_USAGE_LIMIT");
 		else if (TailMatches("FULL|FREEZE|ANALYZE|VERBOSE|DISABLE_PAGE_SKIPPING|SKIP_LOCKED|PROCESS_MAIN|PROCESS_TOAST|TRUNCATE|SKIP_DATABASE_STATS|ONLY_DATABASE_STATS"))
 			COMPLETE_WITH("ON", "OFF");
 		else if (TailMatches("INDEX_CLEANUP"))

src/include/miscadmin.h

@@ -263,6 +263,15 @@ extern PGDLLIMPORT double hash_mem_multiplier;
 extern PGDLLIMPORT int maintenance_work_mem;
 extern PGDLLIMPORT int max_parallel_maintenance_workers;
 
+/*
+ * Upper and lower hard limits for the buffer access strategy ring size
+ * specified by the VacuumBufferUsageLimit GUC and BUFFER_USAGE_LIMIT option
+ * to VACUUM and ANALYZE.
+ */
+#define MIN_BAS_VAC_RING_SIZE_KB 128
+#define MAX_BAS_VAC_RING_SIZE_KB (16 * 1024 * 1024)
+
+extern PGDLLIMPORT int VacuumBufferUsageLimit;
 extern PGDLLIMPORT int VacuumCostPageHit;
 extern PGDLLIMPORT int VacuumCostPageMiss;
 extern PGDLLIMPORT int VacuumCostPageDirty;

src/include/storage/bufmgr.h

@@ -260,7 +260,12 @@ extern Size BufferShmemSize(void);
 extern void AtProcExit_LocalBuffers(void);
 
 /* in freelist.c */
+
 extern BufferAccessStrategy GetAccessStrategy(BufferAccessStrategyType btype);
+extern BufferAccessStrategy GetAccessStrategyWithSize(BufferAccessStrategyType btype,
+													  int ring_size_kb);
+extern int	GetAccessStrategyBufferCount(BufferAccessStrategy strategy);
+
 extern void FreeAccessStrategy(BufferAccessStrategy strategy);
 
 

src/include/utils/guc_hooks.h

@@ -33,6 +33,8 @@ extern bool check_autovacuum_max_workers(int *newval, void **extra,
 										 GucSource source);
 extern bool check_autovacuum_work_mem(int *newval, void **extra,
 									  GucSource source);
+extern bool check_vacuum_buffer_usage_limit(int *newval, void **extra,
+											GucSource source);
 extern bool check_backtrace_functions(char **newval, void **extra,
 									  GucSource source);
 extern void assign_backtrace_functions(const char *newval, void *extra);

src/test/regress/expected/vacuum.out

@@ -350,6 +350,25 @@ SELECT t.relfilenode = :toast_filenode AS is_same_toast_filenode
  f
 (1 row)
 
+-- BUFFER_USAGE_LIMIT option
+VACUUM (BUFFER_USAGE_LIMIT '512 kB') vac_option_tab;
+ANALYZE (BUFFER_USAGE_LIMIT '512 kB') vac_option_tab;
+-- try disabling the buffer usage limit
+VACUUM (BUFFER_USAGE_LIMIT 0) vac_option_tab;
+ANALYZE (BUFFER_USAGE_LIMIT 0) vac_option_tab;
+-- value exceeds max size error
+VACUUM (BUFFER_USAGE_LIMIT 16777220) vac_option_tab;
+ERROR:  buffer_usage_limit option must be 0 or between 128 KB and 16777216 KB
+-- value is less than min size error
+VACUUM (BUFFER_USAGE_LIMIT 120) vac_option_tab;
+ERROR:  buffer_usage_limit option must be 0 or between 128 KB and 16777216 KB
+-- integer overflow error
+VACUUM (BUFFER_USAGE_LIMIT 10000000000) vac_option_tab;
+ERROR:  value: "10000000000": is invalid for buffer_usage_limit
+HINT:  Value exceeds integer range.
+-- incompatible with VACUUM FULL error
+VACUUM (BUFFER_USAGE_LIMIT '512 kB', FULL) vac_option_tab;
+ERROR:  BUFFER_USAGE_LIMIT cannot be specified for VACUUM FULL
 -- SKIP_DATABASE_STATS option
 VACUUM (SKIP_DATABASE_STATS) vactst;
 -- ONLY_DATABASE_STATS option

src/test/regress/sql/vacuum.sql

@@ -272,6 +272,21 @@ SELECT t.relfilenode = :toast_filenode AS is_same_toast_filenode
   FROM pg_class c, pg_class t
   WHERE c.reltoastrelid = t.oid AND c.relname = 'vac_option_tab';
 
+-- BUFFER_USAGE_LIMIT option
+VACUUM (BUFFER_USAGE_LIMIT '512 kB') vac_option_tab;
+ANALYZE (BUFFER_USAGE_LIMIT '512 kB') vac_option_tab;
+-- try disabling the buffer usage limit
+VACUUM (BUFFER_USAGE_LIMIT 0) vac_option_tab;
+ANALYZE (BUFFER_USAGE_LIMIT 0) vac_option_tab;
+-- value exceeds max size error
+VACUUM (BUFFER_USAGE_LIMIT 16777220) vac_option_tab;
+-- value is less than min size error
+VACUUM (BUFFER_USAGE_LIMIT 120) vac_option_tab;
+-- integer overflow error
+VACUUM (BUFFER_USAGE_LIMIT 10000000000) vac_option_tab;
+-- incompatible with VACUUM FULL error
+VACUUM (BUFFER_USAGE_LIMIT '512 kB', FULL) vac_option_tab;
+
 -- SKIP_DATABASE_STATS option
 VACUUM (SKIP_DATABASE_STATS) vactst;