v5-0003-Add-vacuum-db-buffer-usage-limit-option-and-guc.patch

From a38fb38daf476cc4a572757d2634713bc2bd4f8a Mon Sep 17 00:00:00 2001
From: Melanie Plageman <melanieplageman@gmail.com>
Date: Thu, 16 Mar 2023 20:27:51 -0400
Subject: [PATCH v5 3/3] Add vacuum[db] buffer usage limit option and guc

---
 doc/src/sgml/config.sgml                      | 25 +++++++++
 doc/src/sgml/ref/vacuum.sgml                  | 22 ++++++++
 doc/src/sgml/ref/vacuumdb.sgml                | 20 ++++++++
 src/backend/commands/vacuum.c                 | 51 ++++++++++++++++++-
 src/backend/commands/vacuumparallel.c         |  6 ++-
 src/backend/postmaster/autovacuum.c           | 15 +++++-
 src/backend/storage/buffer/README             |  2 +
 src/backend/storage/buffer/freelist.c         | 48 +++++++++++++++++
 src/backend/utils/init/globals.c              |  2 +
 src/backend/utils/misc/guc_tables.c           | 11 ++++
 src/backend/utils/misc/postgresql.conf.sample |  4 ++
 src/bin/psql/tab-complete.c                   |  2 +-
 src/bin/scripts/vacuumdb.c                    | 21 ++++++++
 src/include/commands/vacuum.h                 |  4 ++
 src/include/miscadmin.h                       |  1 +
 src/include/storage/bufmgr.h                  |  5 ++
 16 files changed, 235 insertions(+), 4 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index e5c41cc6c6..241aafddd9 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -1981,6 +1981,31 @@ 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 ring buffer size to be used for a given invocation of
+        <command>VACUUM</command> or instance of autovacuum. This size is
+        converted to a number of shared buffers which will be reused as part of
+        a <literal>Buffer Access Strategy</literal>. <literal>0</literal> will
+        disable use of a <literal>Buffer Access Strategy</literal>.
+        <literal>-1</literal> will set the size to a default of <literal>256
+        kB</literal>. The maximum ring buffer size is <literal>16 GB</literal>.
+        Though you may set <varname>vacuum_buffer_usage_limit</varname> below
+        <literal>128 kB</literal>, it will be clamped to <literal>128
+        kB</literal> at runtime. The default value is <literal>-1</literal>.
+        Without units, the size is taken as <literal>kB</literal>. This
+        parameter can be set at any time.
+       </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>
diff --git a/doc/src/sgml/ref/vacuum.sgml b/doc/src/sgml/ref/vacuum.sgml
index b6d30b5764..216c09c3d7 100644
--- a/doc/src/sgml/ref/vacuum.sgml
+++ b/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 +346,27 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term><literal>BUFFER_USAGE_LIMIT</literal></term>
+    <listitem>
+     <para>
+      Specifies the ring buffer size for <command>VACUUM</command>. This size
+      is used to calculate a number of shared buffers which will be reused as
+      part of a <literal>Buffer Access Strategy</literal>. <literal>0</literal>
+      disables use of a <literal>Buffer Access Strategy</literal>.
+      <literal>-1</literal> indicates that <command>VACUUM</command> should
+      fall back to the value specified by <xref
+      linkend="guc-vacuum-buffer-usage-limit"/>. The maximum value is
+      <literal>16 GB</literal>. Though you may specify a size smaller than
+      <literal>128</literal>, the value will be clamped to <literal>128
+      kB</literal> at runtime. Without units, the size is taken as
+      <literal>kB</literal>. This size applies to a single invocation of
+      <command>VACUUM</command>. The analyze stage and parallel vacuum workers
+      do not use this size.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><replaceable class="parameter">boolean</replaceable></term>
     <listitem>
diff --git a/doc/src/sgml/ref/vacuumdb.sgml b/doc/src/sgml/ref/vacuumdb.sgml
index 74bac2d4ba..5e8a6c167d 100644
--- a/doc/src/sgml/ref/vacuumdb.sgml
+++ b/doc/src/sgml/ref/vacuumdb.sgml
@@ -278,6 +278,26 @@ PostgreSQL documentation
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--buffer-usage-limit <replaceable class="parameter">buffer_usage_limit</replaceable></option></term>
+      <listitem>
+       <para>
+        The size of the ring buffer used for vacuuming. This size is used to
+        calculate a number of shared buffers which will be reused as part of a
+        <literal>Buffer Access Strategy</literal>. <literal>0</literal>
+        disables use of a <literal>Buffer Access Strategy</literal>.
+        <literal>-1</literal> indicates that the vacuum should fall back to the
+        value specified by <xref linkend="guc-vacuum-buffer-usage-limit"/>. The
+        maximum value is <literal>16 GB</literal>. Though you may specify a
+        size smaller than <literal>128 kB</literal>, the value will be clamped
+        to <literal>128 kB</literal> at runtime. Without units, the value is
+        taken as <literal>kB</literal>. This size applies to a single
+        invocation of <command>vacuumdb</command>. The analyze stage and
+        parallel vacuum workers do not use this size.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><option>-n <replaceable class="parameter">schema</replaceable></option></term>
       <term><option>--schema=<replaceable class="parameter">schema</replaceable></option></term>
diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index a6aac30529..f434f07dd1 100644
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -128,6 +128,9 @@ ExecVacuum(ParseState *pstate, VacuumStmt *vacstmt, bool isTopLevel)
 	/* By default parallel vacuum is enabled */
 	params.nworkers = 0;
 
+	/* by default use buffer access strategy with default size */
+	params.ring_size = -1;
+
 	/* Parse options list */
 	foreach(lc, vacstmt->options)
 	{
@@ -211,6 +214,43 @@ ExecVacuum(ParseState *pstate, VacuumStmt *vacstmt, bool isTopLevel)
 			skip_database_stats = defGetBoolean(opt);
 		else if (strcmp(opt->defname, "only_database_stats") == 0)
 			only_database_stats = defGetBoolean(opt);
+		else if (strcmp(opt->defname, "buffer_usage_limit") == 0)
+		{
+			char	   *vac_buffer_size;
+			int			result;
+			const char *hintmsg;
+
+			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 for out-of-bounds */
+			if (result < -1 || result > MAX_BAS_RING_SIZE_KB)
+			{
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+						 errmsg("buffer_usage_limit for a vacuum must be between -1 and %d",
+								MAX_BAS_RING_SIZE_KB)));
+			}
+
+			params.ring_size = result;
+
+		}
 		else
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
@@ -400,7 +440,16 @@ vacuum(List *relations, VacuumParams *params,
 	{
 		MemoryContext old_context = MemoryContextSwitchTo(vac_context);
 
-		bstrategy = GetAccessStrategy(BAS_VACUUM);
+		if (params->ring_size == -1)
+		{
+			if (vacuum_buffer_usage_limit == -1)
+				bstrategy = GetAccessStrategy(BAS_VACUUM);
+			else
+				bstrategy = GetAccessStrategyWithSize(BAS_VACUUM, vacuum_buffer_usage_limit);
+		}
+		else
+			bstrategy = GetAccessStrategyWithSize(BAS_VACUUM, params->ring_size);
+
 		MemoryContextSwitchTo(old_context);
 	}
 
diff --git a/src/backend/commands/vacuumparallel.c b/src/backend/commands/vacuumparallel.c
index bcd40c80a1..16742f6612 100644
--- a/src/backend/commands/vacuumparallel.c
+++ b/src/backend/commands/vacuumparallel.c
@@ -1012,7 +1012,11 @@ 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
+	 * For now, use the default buffer access strategy ring size.
+	 * TODO: should this work differently even though they are only for indexes
+	 */
 	pvs.bstrategy = GetAccessStrategy(BAS_VACUUM);
 
 	/* Setup error traceback support for ereport() */
diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index c0e2e00a7e..7dbd3b8935 100644
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -2291,8 +2291,14 @@ do_autovacuum(void)
 	 * Create a buffer access strategy object for VACUUM to use.  We want to
 	 * use the same one across all the vacuum operations we perform, since the
 	 * point is for VACUUM not to blow out the shared cache.
+	 * If we later enter failsafe mode, we will cease use of the
+	 * BufferAccessStrategy. Either way, we clean up the BufferAccessStrategy
+	 * object at the end of this function.
 	 */
-	bstrategy = GetAccessStrategy(BAS_VACUUM);
+	if (vacuum_buffer_usage_limit == -1)
+		bstrategy = GetAccessStrategy(BAS_VACUUM);
+	else
+		bstrategy = GetAccessStrategyWithSize(BAS_VACUUM, vacuum_buffer_usage_limit);
 
 	/*
 	 * create a memory context to act as fake PortalContext, so that the
@@ -2881,6 +2887,13 @@ table_recheck_autovac(Oid relid, HTAB *table_toast_map,
 		tab->at_params.multixact_freeze_table_age = multixact_freeze_table_age;
 		tab->at_params.is_wraparound = wraparound;
 		tab->at_params.log_min_duration = log_min_duration;
+
+		// TODO: should this be 0 so that we are sure that vacuum() never
+		// allocates a new bstrategy for us, even if we pass in NULL for that
+		// parameter? maybe could change how failsafe NULLs out bstrategy if
+		// so?
+		tab->at_params.ring_size = vacuum_buffer_usage_limit;
+
 		tab->at_vacuum_cost_limit = vac_cost_limit;
 		tab->at_vacuum_cost_delay = vac_cost_delay;
 		tab->at_relname = NULL;
diff --git a/src/backend/storage/buffer/README b/src/backend/storage/buffer/README
index a775276ff2..bf166bbdf1 100644
--- a/src/backend/storage/buffer/README
+++ b/src/backend/storage/buffer/README
@@ -245,6 +245,8 @@ for WAL flushes.  While it's okay for a background vacuum to be slowed by
 doing its own WAL flushing, we'd prefer that COPY not be subject to that,
 so we let it use up a bit more of the buffer arena.
 
+TODO: update with info about new option to control the size
+
 
 Background Writer's Processing
 ------------------------------
diff --git a/src/backend/storage/buffer/freelist.c b/src/backend/storage/buffer/freelist.c
index c690d5f15f..97ca3f344f 100644
--- a/src/backend/storage/buffer/freelist.c
+++ b/src/backend/storage/buffer/freelist.c
@@ -586,6 +586,54 @@ GetAccessStrategy(BufferAccessStrategyType btype)
 	return strategy;
 }
 
+static inline int
+bufsize_limit_to_nbuffers(int bufsize_limit_kb)
+{
+	int			blcksz_kb = BLCKSZ / 1024;
+
+	Assert(blcksz_kb > 0);
+
+	return bufsize_limit_kb / blcksz_kb;
+}
+
+BufferAccessStrategy
+GetAccessStrategyWithSize(BufferAccessStrategyType btype, int ring_size)
+{
+	BufferAccessStrategy strategy;
+	int			nbuffers;
+
+	/* Default nbuffers should have resulted in calling GetAccessStrategy() */
+	// TODO: this being called ring_size and also nbuffers being called
+	// ring_size in GetAccessStrategy is confusing. Rename the member of
+	// BufferAccessStrategy
+	Assert(ring_size != -1);
+
+	if (ring_size == 0)
+		return NULL;
+
+	Assert(ring_size <= MAX_BAS_RING_SIZE_KB);
+
+	// TODO: warn about clamping?
+	if (ring_size < MIN_BAS_RING_SIZE_KB)
+		nbuffers = bufsize_limit_to_nbuffers(MIN_BAS_RING_SIZE_KB);
+	else
+		nbuffers = bufsize_limit_to_nbuffers(ring_size);
+
+	// TODO: make this smaller?
+	nbuffers = Min(NBuffers / 8, nbuffers);
+
+	/* Allocate the object and initialize all elements to zeroes */
+	strategy = (BufferAccessStrategy)
+		palloc0(offsetof(BufferAccessStrategyData, buffers) +
+				nbuffers * sizeof(Buffer));
+
+	/* Set fields that don't start out zero */
+	strategy->btype = btype;
+	strategy->ring_size = nbuffers;
+
+	return strategy;
+}
+
 /*
  * FreeAccessStrategy -- release a BufferAccessStrategy object
  *
diff --git a/src/backend/utils/init/globals.c b/src/backend/utils/init/globals.c
index 1b1d814254..6eca3371bd 100644
--- a/src/backend/utils/init/globals.c
+++ b/src/backend/utils/init/globals.c
@@ -139,6 +139,8 @@ int			max_worker_processes = 8;
 int			max_parallel_workers = 8;
 int			MaxBackends = 0;
 
+int			vacuum_buffer_usage_limit = -1;
+
 int			VacuumCostPageHit = 1;	/* GUC parameters for vacuum */
 int			VacuumCostPageMiss = 2;
 int			VacuumCostPageDirty = 20;
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 1c0583fe26..883ee29d14 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -2206,6 +2206,17 @@ struct config_int ConfigureNamesInt[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"vacuum_buffer_usage_limit", PGC_USERSET, RESOURCES_MEM,
+			gettext_noop("Sets the buffer pool size for VACUUM and autovacuum."),
+			NULL,
+			GUC_UNIT_KB
+		},
+		&vacuum_buffer_usage_limit,
+		-1, -1, MAX_BAS_RING_SIZE_KB,
+		NULL, 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)."),
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index d06074b86f..36273aa47d 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -156,6 +156,10 @@
 					#   mmap
 					# (change requires restart)
 #min_dynamic_shared_memory = 0MB	# (change requires restart)
+#vacuum_buffer_usage_limit = -1 # size of vacuum buffer access strategy ring.
+				# -1 to use default,
+				# 0 to disable vacuum buffer access strategy and use shared buffers
+				# > 0 to specify size
 
 # - Disk -
 
diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
index 42e87b9e49..6fd80dd3c3 100644
--- a/src/bin/psql/tab-complete.c
+++ b/src/bin/psql/tab-complete.c
@@ -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"))
diff --git a/src/bin/scripts/vacuumdb.c b/src/bin/scripts/vacuumdb.c
index 39be265b5b..5b2a5d2858 100644
--- a/src/bin/scripts/vacuumdb.c
+++ b/src/bin/scripts/vacuumdb.c
@@ -46,6 +46,7 @@ typedef struct vacuumingOptions
 	bool		process_main;
 	bool		process_toast;
 	bool		skip_database_stats;
+	char		*buffer_usage_limit;
 } vacuumingOptions;
 
 /* object filter options */
@@ -123,6 +124,7 @@ main(int argc, char *argv[])
 		{"no-truncate", no_argument, NULL, 10},
 		{"no-process-toast", no_argument, NULL, 11},
 		{"no-process-main", no_argument, NULL, 12},
+		{"buffer-usage-limit", required_argument, NULL, 13},
 		{NULL, 0, NULL, 0}
 	};
 
@@ -147,6 +149,7 @@ main(int argc, char *argv[])
 	/* initialize options */
 	memset(&vacopts, 0, sizeof(vacopts));
 	vacopts.parallel_workers = -1;
+	vacopts.buffer_usage_limit = NULL;
 	vacopts.no_index_cleanup = false;
 	vacopts.force_index_cleanup = false;
 	vacopts.do_truncate = true;
@@ -266,6 +269,9 @@ main(int argc, char *argv[])
 			case 12:
 				vacopts.process_main = false;
 				break;
+			case 13:
+				vacopts.buffer_usage_limit = pg_strdup(optarg);
+				break;
 			default:
 				/* getopt_long already emitted a complaint */
 				pg_log_error_hint("Try \"%s --help\" for more information.", progname);
@@ -324,6 +330,9 @@ main(int argc, char *argv[])
 		if (!vacopts.process_toast)
 			pg_fatal("cannot use the \"%s\" option when performing only analyze",
 					 "no-process-toast");
+		if (vacopts.buffer_usage_limit)
+			pg_fatal("cannot use the \"%s\" option when performing only analyze",
+					 "buffer-usage-limit");
 		/* allow 'and_analyze' with 'analyze_only' */
 	}
 
@@ -550,6 +559,10 @@ vacuum_one_database(ConnParams *cparams,
 		pg_fatal("cannot use the \"%s\" option on server versions older than PostgreSQL %s",
 				 "--parallel", "13");
 
+	if (vacopts->buffer_usage_limit && PQserverVersion(conn) < 160000)
+		pg_fatal("cannot use the \"%s\" option on server versions older than PostgreSQL %s",
+				 "--buffer-usage-limit", "16");
+
 	/* skip_database_stats is used automatically if server supports it */
 	vacopts->skip_database_stats = (PQserverVersion(conn) >= 160000);
 
@@ -1048,6 +1061,13 @@ prepare_vacuum_command(PQExpBuffer sql, int serverVersion,
 								  vacopts->parallel_workers);
 				sep = comma;
 			}
+			if (vacopts->buffer_usage_limit)
+			{
+				Assert(serverVersion >= 160000);
+				appendPQExpBuffer(sql, "%sBUFFER_USAGE_LIMIT '%s'", sep,
+								  vacopts->buffer_usage_limit);
+				sep = comma;
+			}
 			if (sep != paren)
 				appendPQExpBufferChar(sql, ')');
 		}
@@ -1111,6 +1131,7 @@ help(const char *progname)
 	printf(_("      --force-index-cleanup       always remove index entries that point to dead tuples\n"));
 	printf(_("  -j, --jobs=NUM                  use this many concurrent connections to vacuum\n"));
 	printf(_("      --min-mxid-age=MXID_AGE     minimum multixact ID age of tables to vacuum\n"));
+	printf(_("      --buffer-usage-limit=BUFSIZE size of ring buffer used for vacuum\n"));
 	printf(_("      --min-xid-age=XID_AGE       minimum transaction ID age of tables to vacuum\n"));
 	printf(_("      --no-index-cleanup          don't remove index entries that point to dead tuples\n"));
 	printf(_("      --no-process-main           skip the main relation\n"));
diff --git a/src/include/commands/vacuum.h b/src/include/commands/vacuum.h
index bdfd96cfec..d8fba51d82 100644
--- a/src/include/commands/vacuum.h
+++ b/src/include/commands/vacuum.h
@@ -213,6 +213,9 @@ typedef enum VacOptValue
  *
  * Note that at least one of VACOPT_VACUUM and VACOPT_ANALYZE must be set
  * in options.
+ *
+ * When adding a new VacuumParam member, consider adding it to vacuumdb as
+ * well.
  */
 typedef struct VacuumParams
 {
@@ -236,6 +239,7 @@ typedef struct VacuumParams
 	 * disabled.
 	 */
 	int			nworkers;
+	int			ring_size;
 } VacuumParams;
 
 /*
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 06a86f9ac1..b572dfcc6c 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -262,6 +262,7 @@ extern PGDLLIMPORT int work_mem;
 extern PGDLLIMPORT double hash_mem_multiplier;
 extern PGDLLIMPORT int maintenance_work_mem;
 extern PGDLLIMPORT int max_parallel_maintenance_workers;
+extern PGDLLIMPORT int vacuum_buffer_usage_limit;
 
 extern PGDLLIMPORT int VacuumCostPageHit;
 extern PGDLLIMPORT int VacuumCostPageMiss;
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index b8a18b8081..338de38568 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -101,6 +101,9 @@ extern PGDLLIMPORT int32 *LocalRefCount;
 /* upper limit for effective_io_concurrency */
 #define MAX_IO_CONCURRENCY 1000
 
+#define MAX_BAS_RING_SIZE_KB (16 * 1024 * 1024)
+#define MIN_BAS_RING_SIZE_KB 128
+
 /* special block number for ReadBuffer() */
 #define P_NEW	InvalidBlockNumber	/* grow the file to get a new page */
 
@@ -196,6 +199,8 @@ extern void AtProcExit_LocalBuffers(void);
 
 /* in freelist.c */
 extern BufferAccessStrategy GetAccessStrategy(BufferAccessStrategyType btype);
+
+extern BufferAccessStrategy GetAccessStrategyWithSize(BufferAccessStrategyType btype, int nbuffers);
 extern void FreeAccessStrategy(BufferAccessStrategy strategy);
 
 
-- 
2.37.2