brin autosummarization -- autovacuum "work items"

diff --git a/doc/src/sgml/brin.sgml b/doc/src/sgml/brin.sgml
index 5bf11dc..5140a38 100644
--- a/doc/src/sgml/brin.sgml
+++ b/doc/src/sgml/brin.sgml
@@ -74,9 +74,14 @@
    tuple; those tuples remain unsummarized until a summarization run is
    invoked later, creating initial summaries.
    This process can be invoked manually using the
-   <function>brin_summarize_new_values(regclass)</function> function,
-   or automatically when <command>VACUUM</command> processes the table.
+   <function>brin_summarize_range(regclass, bigint)</function> or
+   <function>brin_summarize_new_values(regclass)</function> functions;
+   automatically when <command>VACUUM</command> processes the table;
+   or by automatic summarization executed by autovacuum, as insertions
+   occur.  (This last trigger is disabled by default and can be enabled
+   with the <literal>autosummarize</literal> parameter.)
   </para>
+
  </sect2>
 </sect1>
 
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 6887eab..25c18d1 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -19685,6 +19685,13 @@ postgres=# SELECT * FROM pg_walfile_name_offset(pg_stop_backup());
       </row>
       <row>
        <entry>
+        <literal><function>brin_summarize_range(<parameter>index</> <type>regclass</>, <parameter>blockNumber</> <type>bigint</type>)</function></literal>
+       </entry>
+       <entry><type>integer</type></entry>
+       <entry>summarize the page range covering the given block, if not already summarized</entry>
+      </row>
+      <row>
+       <entry>
         <literal><function>gin_clean_pending_list(<parameter>index</> <type>regclass</>)</function></literal>
        </entry>
        <entry><type>bigint</type></entry>
@@ -19700,7 +19707,8 @@ postgres=# SELECT * FROM pg_walfile_name_offset(pg_stop_backup());
     that are not currently summarized by the index; for any such range
     it creates a new summary index tuple by scanning the table pages.
     It returns the number of new page range summaries that were inserted
-    into the index.
+    into the index.  <function>brin_summarize_range</> does the same, except
+    it only summarizes the range that covers the given block number.
    </para>
 
    <para>
diff --git a/doc/src/sgml/ref/create_index.sgml b/doc/src/sgml/ref/create_index.sgml
index 7163b03..83ee7d3 100644
--- a/doc/src/sgml/ref/create_index.sgml
+++ b/doc/src/sgml/ref/create_index.sgml
@@ -382,7 +382,7 @@ CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] [ [ IF NOT EXISTS ] <replaceable class=
    </variablelist>
 
    <para>
-    <acronym>BRIN</> indexes accept a different parameter:
+    <acronym>BRIN</> indexes accept different parameters:
    </para>
 
    <variablelist>
@@ -396,6 +396,16 @@ CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] [ [ IF NOT EXISTS ] <replaceable class=
     </para>
     </listitem>
    </varlistentry>
+
+   <varlistentry>
+    <term><literal>autosummarize</></term>
+    <listitem>
+    <para>
+     Defines whether a summarization run is invoked for the previous page
+     range whenever an insertion is detected on the next one.
+    </para>
+    </listitem>
+   </varlistentry>
    </variablelist>
   </refsect2>
 
diff --git a/src/backend/access/brin/brin.c b/src/backend/access/brin/brin.c
index b22563b..707d04e 100644
--- a/src/backend/access/brin/brin.c
+++ b/src/backend/access/brin/brin.c
@@ -26,6 +26,7 @@
 #include "catalog/pg_am.h"
 #include "miscadmin.h"
 #include "pgstat.h"
+#include "postmaster/autovacuum.h"
 #include "storage/bufmgr.h"
 #include "storage/freespace.h"
 #include "utils/builtins.h"
@@ -60,10 +61,12 @@ typedef struct BrinOpaque
 	BrinDesc   *bo_bdesc;
 } BrinOpaque;
 
+#define BRIN_ALL_BLOCKRANGES	InvalidBlockNumber
+
 static BrinBuildState *initialize_brin_buildstate(Relation idxRel,
 						   BrinRevmap *revmap, BlockNumber pagesPerRange);
 static void terminate_brin_buildstate(BrinBuildState *state);
-static void brinsummarize(Relation index, Relation heapRel,
+static void brinsummarize(Relation index, Relation heapRel, BlockNumber pageRange,
 			  double *numSummarized, double *numExisting);
 static void form_and_insert_tuple(BrinBuildState *state);
 static void union_tuples(BrinDesc *bdesc, BrinMemTuple *a,
@@ -126,8 +129,11 @@ brinhandler(PG_FUNCTION_ARGS)
  * with those of the new tuple.  If the tuple values are not consistent with
  * the summary tuple, we need to update the index tuple.
  *
+ * If autosummarization is enabled, check if we need to summarize the previous
+ * page range.
+ *
  * If the range is not currently summarized (i.e. the revmap returns NULL for
- * it), there's nothing to do.
+ * it), there's nothing to do for this tuple.
  */
 bool
 brininsert(Relation idxRel, Datum *values, bool *nulls,
@@ -136,30 +142,57 @@ brininsert(Relation idxRel, Datum *values, bool *nulls,
 		   IndexInfo *indexInfo)
 {
 	BlockNumber pagesPerRange;
+	BlockNumber	origHeapBlk;
+	BlockNumber	heapBlk;
 	BrinDesc   *bdesc = (BrinDesc *) indexInfo->ii_AmCache;
 	BrinRevmap *revmap;
 	Buffer		buf = InvalidBuffer;
 	MemoryContext tupcxt = NULL;
 	MemoryContext oldcxt = CurrentMemoryContext;
+	bool		autosummarize = BrinGetAutoSummarize(idxRel);
 
 	revmap = brinRevmapInitialize(idxRel, &pagesPerRange, NULL);
 
+	/*
+	 * origHeapBlk is the block number where the insertion occurred.  heapBlk
+	 * is the first block in the corresponding page range.
+	 */
+	origHeapBlk = ItemPointerGetBlockNumber(heaptid);
+	heapBlk = (origHeapBlk / pagesPerRange) * pagesPerRange;
+
 	for (;;)
 	{
 		bool		need_insert = false;
 		OffsetNumber off;
-		BrinTuple  *brtup;
+		BrinTuple  *brtup = NULL;
 		BrinMemTuple *dtup;
-		BlockNumber heapBlk;
 		int			keyno;
 
 		CHECK_FOR_INTERRUPTS();
 
-		heapBlk = ItemPointerGetBlockNumber(heaptid);
-		/* normalize the block number to be the first block in the range */
-		heapBlk = (heapBlk / pagesPerRange) * pagesPerRange;
-		brtup = brinGetTupleForHeapBlock(revmap, heapBlk, &buf, &off, NULL,
-										 BUFFER_LOCK_SHARE, NULL);
+		/*
+		 * If auto-summarization is enabled and we just inserted the first
+		 * tuple into the first block of a new non-first page range, request a
+		 * summarization run of the previous range.
+		 */
+		if (autosummarize &&
+			heapBlk > 0 &&
+			heapBlk == origHeapBlk &&
+			ItemPointerGetOffsetNumber(heaptid) == FirstOffsetNumber)
+		{
+			BlockNumber lastPageRange = heapBlk - 1;
+
+			brtup = brinGetTupleForHeapBlock(revmap, lastPageRange, &buf, &off, NULL,
+											 BUFFER_LOCK_SHARE, NULL);
+			if (!brtup)
+				AutoVacuumRequestWork(AVW_BRINSummarizeRange,
+									  RelationGetRelid(idxRel),
+									  lastPageRange);
+		}
+
+		if (!brtup)
+			brtup = brinGetTupleForHeapBlock(revmap, heapBlk, &buf, &off,
+											 NULL, BUFFER_LOCK_SHARE, NULL);
 
 		/* if range is unsummarized, there's nothing to do */
 		if (!brtup)
@@ -664,9 +697,6 @@ brinbuild(Relation heap, Relation index, IndexInfo *indexInfo)
 	reltuples = IndexBuildHeapScan(heap, index, indexInfo, false,
 								   brinbuildCallback, (void *) state);
 
-	/* process the final batch */
-	form_and_insert_tuple(state);
-
 	/* release resources */
 	idxtuples = state->bs_numtuples;
 	brinRevmapTerminate(state->bs_rmAccess);
@@ -747,7 +777,7 @@ brinvacuumcleanup(IndexVacuumInfo *info, IndexBulkDeleteResult *stats)
 
 	brin_vacuum_scan(info->index, info->strategy);
 
-	brinsummarize(info->index, heapRel,
+	brinsummarize(info->index, heapRel, BRIN_ALL_BLOCKRANGES,
 				  &stats->num_index_tuples, &stats->num_index_tuples);
 
 	heap_close(heapRel, AccessShareLock);
@@ -765,7 +795,8 @@ brinoptions(Datum reloptions, bool validate)
 	BrinOptions *rdopts;
 	int			numoptions;
 	static const relopt_parse_elt tab[] = {
-		{"pages_per_range", RELOPT_TYPE_INT, offsetof(BrinOptions, pagesPerRange)}
+		{"pages_per_range", RELOPT_TYPE_INT, offsetof(BrinOptions, pagesPerRange)},
+		{"autosummarize", RELOPT_TYPE_BOOL, offsetof(BrinOptions, autosummarize)}
 	};
 
 	options = parseRelOptions(reloptions, validate, RELOPT_KIND_BRIN,
@@ -792,12 +823,35 @@ brinoptions(Datum reloptions, bool validate)
 Datum
 brin_summarize_new_values(PG_FUNCTION_ARGS)
 {
+	Datum	relation = PG_GETARG_DATUM(0);
+
+	return DirectFunctionCall2(brin_summarize_range,
+							   relation,
+							   Int64GetDatum((int64) BRIN_ALL_BLOCKRANGES));
+}
+
+/*
+ * SQL-callable function to summarize the indicated page range, if not already
+ * summarized.  If the second argument is BRIN_ALL_BLOCKRANGES, all
+ * unsummarized ranges are summarized.
+ */
+Datum
+brin_summarize_range(PG_FUNCTION_ARGS)
+{
 	Oid			indexoid = PG_GETARG_OID(0);
+	int64		heapBlk64 = PG_GETARG_INT64(1);
+	BlockNumber	heapBlk;
 	Oid			heapoid;
 	Relation	indexRel;
 	Relation	heapRel;
 	double		numSummarized = 0;
 
+	if (heapBlk64 > BRIN_ALL_BLOCKRANGES || heapBlk64 < 0)
+		ereport(ERROR,
+				(errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
+				 errmsg("invalid block number " INT64_FORMAT, heapBlk64)));
+	heapBlk = (BlockNumber) heapBlk64;
+
 	/*
 	 * We must lock table before index to avoid deadlocks.  However, if the
 	 * passed indexoid isn't an index then IndexGetRelation() will fail.
@@ -837,7 +891,7 @@ brin_summarize_new_values(PG_FUNCTION_ARGS)
 						RelationGetRelationName(indexRel))));
 
 	/* OK, do it */
-	brinsummarize(indexRel, heapRel, &numSummarized, NULL);
+	brinsummarize(indexRel, heapRel, heapBlk, &numSummarized, NULL);
 
 	relation_close(indexRel, ShareUpdateExclusiveLock);
 	relation_close(heapRel, ShareUpdateExclusiveLock);
@@ -1063,17 +1117,17 @@ summarize_range(IndexInfo *indexInfo, BrinBuildState *state, Relation heapRel,
 }
 
 /*
- * Scan a complete BRIN index, and summarize each page range that's not already
- * summarized.  The index and heap must have been locked by caller in at
- * least ShareUpdateExclusiveLock mode.
+ * Summarize page ranges that are not already summarized.  If pageRange is
+ * BRIN_ALL_BLOCKRANGES then the whole table is scanned; otherwise, only the
+ * page range containing the given heap page number is scanned.
  *
  * For each new index tuple inserted, *numSummarized (if not NULL) is
  * incremented; for each existing tuple, *numExisting (if not NULL) is
  * incremented.
  */
 static void
-brinsummarize(Relation index, Relation heapRel, double *numSummarized,
-			  double *numExisting)
+brinsummarize(Relation index, Relation heapRel, BlockNumber pageRange,
+			  double *numSummarized, double *numExisting)
 {
 	BrinRevmap *revmap;
 	BrinBuildState *state = NULL;
@@ -1082,15 +1136,40 @@ brinsummarize(Relation index, Relation heapRel, double *numSummarized,
 	BlockNumber heapBlk;
 	BlockNumber pagesPerRange;
 	Buffer		buf;
+	BlockNumber startBlk;
+	BlockNumber endBlk;
+
+	/* determine range of pages to process; nothing to do for an empty table */
+	heapNumBlocks = RelationGetNumberOfBlocks(heapRel);
+	if (heapNumBlocks == 0)
+		return;
 
 	revmap = brinRevmapInitialize(index, &pagesPerRange, NULL);
 
+	if (pageRange == BRIN_ALL_BLOCKRANGES)
+	{
+		startBlk = 0;
+		endBlk = heapNumBlocks;
+	}
+	else
+	{
+		startBlk = (pageRange / pagesPerRange) * pagesPerRange;
+		/* Nothing to do if start point is beyond end of table */
+		if (startBlk > heapNumBlocks)
+		{
+			brinRevmapTerminate(revmap);
+			return;
+		}
+		endBlk = startBlk + pagesPerRange;
+		if (endBlk > heapNumBlocks)
+			endBlk = heapNumBlocks;
+	}
+
 	/*
 	 * Scan the revmap to find unsummarized items.
 	 */
 	buf = InvalidBuffer;
-	heapNumBlocks = RelationGetNumberOfBlocks(heapRel);
-	for (heapBlk = 0; heapBlk < heapNumBlocks; heapBlk += pagesPerRange)
+	for (heapBlk = startBlk; heapBlk < endBlk; heapBlk += pagesPerRange)
 	{
 		BrinTuple  *tup;
 		OffsetNumber off;
diff --git a/src/backend/access/brin/brin_revmap.c b/src/backend/access/brin/brin_revmap.c
index 0de6999..3937ffd 100644
--- a/src/backend/access/brin/brin_revmap.c
+++ b/src/backend/access/brin/brin_revmap.c
@@ -205,7 +205,11 @@ brinGetTupleForHeapBlock(BrinRevmap *revmap, BlockNumber heapBlk,
 	/* normalize the heap block number to be the first page in the range */
 	heapBlk = (heapBlk / revmap->rm_pagesPerRange) * revmap->rm_pagesPerRange;
 
-	/* Compute the revmap page number we need */
+	/*
+	 * Compute the revmap page number we need.  If Invalid is returned (i.e.,
+	 * the revmap page hasn't been created yet), the requested page range is
+	 * not summarized.
+	 */
 	mapBlk = revmap_get_blkno(revmap, heapBlk);
 	if (mapBlk == InvalidBlockNumber)
 	{
@@ -281,13 +285,13 @@ brinGetTupleForHeapBlock(BrinRevmap *revmap, BlockNumber heapBlk,
 			{
 				tup = (BrinTuple *) PageGetItem(page, lp);
 
-				if (tup->bt_blkno == heapBlk)
-				{
-					if (size)
-						*size = ItemIdGetLength(lp);
-					/* found it! */
-					return tup;
-				}
+				if (tup->bt_blkno != heapBlk)
+					elog(ERROR, "expected blkno %u, got %u", heapBlk, tup->bt_blkno);
+
+				if (size)
+					*size = ItemIdGetLength(lp);
+				/* found it! */
+				return tup;
 			}
 		}
 
diff --git a/src/backend/access/common/reloptions.c b/src/backend/access/common/reloptions.c
index 72e1253..9da287d 100644
--- a/src/backend/access/common/reloptions.c
+++ b/src/backend/access/common/reloptions.c
@@ -94,6 +94,15 @@ static relopt_bool boolRelOpts[] =
 {
 	{
 		{
+			"autosummarize",
+			"Enables automatic summarization on this BRIN index",
+			RELOPT_KIND_BRIN,
+			AccessExclusiveLock
+		},
+		false
+	},
+	{
+		{
 			"autovacuum_enabled",
 			"Enables autovacuum in this relation",
 			RELOPT_KIND_HEAP | RELOPT_KIND_TOAST,
diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index 33ca749..6f4b6e8 100644
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -92,7 +92,9 @@
 #include "storage/procsignal.h"
 #include "storage/sinvaladt.h"
 #include "tcop/tcopprot.h"
+#include "utils/dsa.h"
 #include "utils/fmgroids.h"
+#include "utils/fmgrprotos.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
 #include "utils/ps_status.h"
@@ -252,9 +254,10 @@ typedef enum
  * av_runningWorkers the WorkerInfo non-free queue
  * av_startingWorker pointer to WorkerInfo currently being started (cleared by
  *					the worker itself as soon as it's up and running)
+ * av_dsa_handle	handle for allocatable shared memory
  *
  * This struct is protected by AutovacuumLock, except for av_signal and parts
- * of the worker list (see above).
+ * of the worker list (see above).  av_dsa_handle is readable unlocked.
  *-------------
  */
 typedef struct
@@ -264,6 +267,8 @@ typedef struct
 	dlist_head	av_freeWorkers;
 	dlist_head	av_runningWorkers;
 	WorkerInfo	av_startingWorker;
+	dsa_handle	av_dsa_handle;
+	dsa_pointer	av_workitems;
 } AutoVacuumShmemStruct;
 
 static AutoVacuumShmemStruct *AutoVacuumShmem;
@@ -278,6 +283,32 @@ static MemoryContext DatabaseListCxt = NULL;
 /* Pointer to my own WorkerInfo, valid on each worker */
 static WorkerInfo MyWorkerInfo = NULL;
 
+/*
+ * Autovacuum workitem array, stored in AutoVacuumShmem->av_workitems.  This
+ * list is mostly protected by AutovacuumLock, except that if it's marked
+ * 'active' other processes must not modify the work-identifying members,
+ * though changing the list pointers is okay.
+ */
+typedef struct AutoVacuumWorkItem
+{
+	AutoVacuumWorkItemType avw_type;
+	Oid			avw_database;
+	Oid			avw_relation;
+	BlockNumber	avw_blockNumber;
+	bool		avw_active;
+	dsa_pointer	avw_next;	/* doubly linked list pointers */
+	dsa_pointer	avw_prev;
+} AutoVacuumWorkItem;
+
+#define NUM_WORKITEMS	256
+typedef struct
+{
+	dsa_pointer		avs_usedItems;
+	dsa_pointer		avs_freeItems;
+} AutovacWorkItems;
+
+static dsa_area	*AutoVacuumDSA = NULL;
+
 /* PID of launcher, valid only in worker while shutting down */
 int			AutovacuumLauncherPid = 0;
 
@@ -316,11 +347,16 @@ static AutoVacOpts *extract_autovac_opts(HeapTuple tup,
 static PgStat_StatTabEntry *get_pgstat_tabentry_relid(Oid relid, bool isshared,
 						  PgStat_StatDBEntry *shared,
 						  PgStat_StatDBEntry *dbentry);
+static void perform_work_item(AutoVacuumWorkItem *workitem);
 static void autovac_report_activity(autovac_table *tab);
+static void autovac_report_workitem(AutoVacuumWorkItem *workitem,
+						const char *nspname, const char *relname);
 static void av_sighup_handler(SIGNAL_ARGS);
 static void avl_sigusr2_handler(SIGNAL_ARGS);
 static void avl_sigterm_handler(SIGNAL_ARGS);
 static void autovac_refresh_stats(void);
+static void remove_wi_from_list(dsa_pointer *list, dsa_pointer wi_ptr);
+static void add_wi_to_list(dsa_pointer *list, dsa_pointer wi_ptr);
 
 
 
@@ -574,6 +610,28 @@ AutoVacLauncherMain(int argc, char *argv[])
 	 */
 	rebuild_database_list(InvalidOid);
 
+	/*
+	 * Set up our DSA so that backends can install work-item requests.  It may
+	 * already exist as created by a previous launcher.
+	 */
+	if (!AutoVacuumShmem->av_dsa_handle)
+	{
+		LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
+		AutoVacuumDSA = dsa_create(LWTRANCHE_AUTOVACUUM);
+		/* make sure it doesn't go away even if we do */
+		dsa_pin(AutoVacuumDSA);
+		dsa_pin_mapping(AutoVacuumDSA);
+		AutoVacuumShmem->av_dsa_handle = dsa_get_handle(AutoVacuumDSA);
+		/* delay array allocation until first request */
+		AutoVacuumShmem->av_workitems = InvalidDsaPointer;
+		LWLockRelease(AutovacuumLock);
+	}
+	else
+	{
+		AutoVacuumDSA = dsa_attach(AutoVacuumShmem->av_dsa_handle);
+		dsa_pin_mapping(AutoVacuumDSA);
+	}
+
 	/* loop until shutdown request */
 	while (!got_SIGTERM)
 	{
@@ -1617,6 +1675,14 @@ AutoVacWorkerMain(int argc, char *argv[])
 	{
 		char		dbname[NAMEDATALEN];
 
+		if (AutoVacuumShmem->av_dsa_handle)
+		{
+			/* First use of DSA in this worker, so attach to it */
+			Assert(!AutoVacuumDSA);
+			AutoVacuumDSA = dsa_attach(AutoVacuumShmem->av_dsa_handle);
+			dsa_pin_mapping(AutoVacuumDSA);
+		}
+
 		/*
 		 * Report autovac startup to the stats collector.  We deliberately do
 		 * this before InitPostgres, so that the last_autovac_time will get
@@ -2467,6 +2533,69 @@ deleted:
 	}
 
 	/*
+	 * Perform additional work items, as requested by backends.
+	 */
+	if (AutoVacuumShmem->av_workitems)
+	{
+		dsa_pointer		wi_ptr;
+		AutovacWorkItems *workitems;
+
+		LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
+
+		/*
+		 * Scan the list of pending items, and process the inactive ones in our
+		 * database.
+		 */
+		workitems = (AutovacWorkItems *)
+			dsa_get_address(AutoVacuumDSA, AutoVacuumShmem->av_workitems);
+		wi_ptr = workitems->avs_usedItems;
+
+		while (wi_ptr != InvalidDsaPointer)
+		{
+			AutoVacuumWorkItem	*workitem;
+
+			workitem = (AutoVacuumWorkItem *)
+				dsa_get_address(AutoVacuumDSA, wi_ptr);
+
+			if (workitem->avw_database == MyDatabaseId && !workitem->avw_active)
+			{
+				dsa_pointer		next_ptr;
+
+				/* claim this one */
+				workitem->avw_active = true;
+
+				LWLockRelease(AutovacuumLock);
+
+				perform_work_item(workitem);
+
+				/*
+				 * Check for config changes before acquiring lock for further
+				 * jobs.
+				 */
+				CHECK_FOR_INTERRUPTS();
+				if (got_SIGHUP)
+				{
+					got_SIGHUP = false;
+					ProcessConfigFile(PGC_SIGHUP);
+				}
+
+				LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
+
+				/* Put the array item back for the next user */
+				next_ptr = workitem->avw_next;
+				remove_wi_from_list(&workitems->avs_usedItems, wi_ptr);
+				add_wi_to_list(&workitems->avs_freeItems, wi_ptr);
+				wi_ptr = next_ptr;
+			}
+			else
+				wi_ptr = workitem->avw_next;
+		}
+
+		/* all done */
+		LWLockRelease(AutovacuumLock);
+	}
+
+	/*
 	 * We leak table_toast_map here (among other things), but since we're
 	 * going away soon, it's not a problem.
 	 */
@@ -2499,6 +2628,103 @@ deleted:
 }
 
 /*
+ * Execute a previously registered work item.
+ */
+static void
+perform_work_item(AutoVacuumWorkItem *workitem)
+{
+	char	   *cur_datname = NULL;
+	char	   *cur_nspname = NULL;
+	char	   *cur_relname = NULL;
+
+	/*
+	 * Note we do not store table info in MyWorkerInfo, since this is not
+	 * vacuuming proper.
+	 */
+
+	/*
+	 * Save the relation name for a possible error message, to avoid a
+	 * catalog lookup in case of an error.  If any of these return NULL,
+	 * then the relation has been dropped since last we checked; skip it.
+	 * Note: they must live in a long-lived memory context because we call
+	 * vacuum and analyze in different transactions.
+	 */
+
+	cur_relname = get_rel_name(workitem->avw_relation);
+	cur_nspname = get_namespace_name(get_rel_namespace(workitem->avw_relation));
+	cur_datname = get_database_name(MyDatabaseId);
+	if (!cur_relname || !cur_nspname || !cur_datname)
+		goto deleted2;
+
+	autovac_report_workitem(workitem, cur_nspname, cur_datname);
+
+	/*
+	 * We will abort the current work item if something errors out, and
+	 * continue with the next one; in particular, this happens if we are
+	 * interrupted with SIGINT.  Note that this means that the work item list
+	 * can be lossy.
+	 */
+	PG_TRY();
+	{
+		/* have at it */
+		MemoryContextSwitchTo(TopTransactionContext);
+
+		switch (workitem->avw_type)
+		{
+			case AVW_BRINSummarizeRange:
+				DirectFunctionCall2(brin_summarize_range,
+									ObjectIdGetDatum(workitem->avw_relation),
+									Int64GetDatum((int64) workitem->avw_blockNumber));
+				break;
+			default:
+				elog(WARNING, "unrecognized work item found: type %d",
+					 workitem->avw_type);
+				break;
+		}
+
+		/*
+		 * Clear a possible query-cancel signal, to avoid a late reaction
+		 * to an automatically-sent signal because of vacuuming the
+		 * current table (we're done with it, so it would make no sense to
+		 * cancel at this point.)
+		 */
+		QueryCancelPending = false;
+	}
+	PG_CATCH();
+	{
+		/*
+		 * Abort the transaction, start a new one, and proceed with the
+		 * next table in our list.
+		 */
+		HOLD_INTERRUPTS();
+		errcontext("processing work entry for relation \"%s.%s.%s\"",
+				   cur_datname, cur_nspname, cur_relname);
+		EmitErrorReport();
+
+		/* this resets the PGXACT flags too */
+		AbortOutOfAnyTransaction();
+		FlushErrorState();
+		MemoryContextResetAndDeleteChildren(PortalContext);
+
+		/* restart our transaction for the following operations */
+		StartTransactionCommand();
+		RESUME_INTERRUPTS();
+	}
+	PG_END_TRY();
+
+	/* We intentionally do not set did_vacuum here */
+
+	/* be tidy */
+deleted2:
+	if (cur_datname)
+		pfree(cur_datname);
+	if (cur_nspname)
+		pfree(cur_nspname);
+	if (cur_relname)
+		pfree(cur_relname);
+}
+
+/*
  * extract_autovac_opts
  *
  * Given a relation's pg_class tuple, return the AutoVacOpts portion of
@@ -2946,6 +3172,45 @@ autovac_report_activity(autovac_table *tab)
 }
 
 /*
+ * autovac_report_workitem
+ *		Report to pgstat that autovacuum is processing a work item
+ */
+static void
+autovac_report_workitem(AutoVacuumWorkItem *workitem,
+						const char *nspname, const char *relname)
+{
+	char	activity[MAX_AUTOVAC_ACTIV_LEN + 12 + 2];
+	char	blk[12 + 2];
+	int		len;
+
+	switch (workitem->avw_type)
+	{
+		case AVW_BRINSummarizeRange:
+			snprintf(activity, MAX_AUTOVAC_ACTIV_LEN,
+					 "autovacuum: BRIN summarize");
+			break;
+	}
+
+	/*
+	 * Report the qualified name of the relation, and the block number if any
+	 */
+	len = strlen(activity);
+
+	if (BlockNumberIsValid(workitem->avw_blockNumber))
+		snprintf(blk, sizeof(blk), " %u", workitem->avw_blockNumber);
+	else
+		blk[0] = '\0';
+
+	snprintf(activity + len, MAX_AUTOVAC_ACTIV_LEN - len,
+			 " %s.%s%s", nspname, relname, blk);
+
+	/* Set statement_timestamp() to current time for pg_stat_activity */
+	SetCurrentStatementStartTimestamp();
+
+	pgstat_report_activity(STATE_RUNNING, activity);
+}
+
+/*
  * AutoVacuumingActive
  *		Check GUC vars and report whether the autovacuum process should be
  *		running.
@@ -2959,6 +3224,113 @@ AutoVacuumingActive(void)
 }
 
 /*
+ * Request one work item to the next autovacuum run processing our database.
+ */
+void
+AutoVacuumRequestWork(AutoVacuumWorkItemType type, Oid relationId,
+					  BlockNumber blkno)
+{
+	AutovacWorkItems *workitems;
+	dsa_pointer		wi_ptr;
+	AutoVacuumWorkItem *workitem;
+
+	LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
+
+	/*
+	 * It may be useful to de-duplicate the list upon insertion.  For the only
+	 * currently existing caller, this is not necessary.
+	 */
+
+	/* First use in this process?  Set up DSA */
+	if (!AutoVacuumDSA)
+	{
+		if (!AutoVacuumShmem->av_dsa_handle)
+		{
+			/* autovacuum launcher not started; nothing can be done */
+			LWLockRelease(AutovacuumLock);
+			return;
+		}
+		AutoVacuumDSA = dsa_attach(AutoVacuumShmem->av_dsa_handle);
+		dsa_pin_mapping(AutoVacuumDSA);
+	}
+
+	/* First use overall?  Allocate work items array */
+	if (AutoVacuumShmem->av_workitems == InvalidDsaPointer)
+	{
+		int		i;
+		AutovacWorkItems *workitems;
+
+		AutoVacuumShmem->av_workitems =
+			dsa_allocate_extended(AutoVacuumDSA,
+								  sizeof(AutovacWorkItems) +
+								  NUM_WORKITEMS * sizeof(AutoVacuumWorkItem),
+								  DSA_ALLOC_NO_OOM);
+		/* if out of memory, silently disregard the request */
+		if (AutoVacuumShmem->av_workitems == InvalidDsaPointer)
+		{
+			LWLockRelease(AutovacuumLock);
+			dsa_detach(AutoVacuumDSA);
+			AutoVacuumDSA = NULL;
+			return;
+		}
+
+		/* Initialize each array entry as a member of the free list */
+		workitems = dsa_get_address(AutoVacuumDSA, AutoVacuumShmem->av_workitems);
+
+		workitems->avs_usedItems = InvalidDsaPointer;
+		workitems->avs_freeItems = InvalidDsaPointer;
+		for (i = 0; i < NUM_WORKITEMS; i++)
+		{
+			/* XXX surely there is a simpler way to do this */
+			wi_ptr = AutoVacuumShmem->av_workitems + sizeof(AutovacWorkItems) +
+				sizeof(AutoVacuumWorkItem) * i;
+			workitem = (AutoVacuumWorkItem *) dsa_get_address(AutoVacuumDSA, wi_ptr);
+
+			workitem->avw_type = 0;
+			workitem->avw_database = InvalidOid;
+			workitem->avw_relation = InvalidOid;
+			workitem->avw_active = false;
+
+			/* put this item in the free list */
+			workitem->avw_next = workitems->avs_freeItems;
+			workitems->avs_freeItems = wi_ptr;
+		}
+	}
+
+	workitems = (AutovacWorkItems *)
+		dsa_get_address(AutoVacuumDSA, AutoVacuumShmem->av_workitems);
+
+	/* If array is full, disregard the request */
+	if (workitems->avs_freeItems == InvalidDsaPointer)
+	{
+		LWLockRelease(AutovacuumLock);
+		dsa_detach(AutoVacuumDSA);
+		AutoVacuumDSA = NULL;
+		return;
+	}
+
+	/* remove workitem struct from free list ... */
+	wi_ptr = workitems->avs_freeItems;
+	remove_wi_from_list(&workitems->avs_freeItems, wi_ptr);
+
+	/* ... initialize it ... */
+	workitem = dsa_get_address(AutoVacuumDSA, wi_ptr);
+	workitem->avw_type = type;
+	workitem->avw_database = MyDatabaseId;
+	workitem->avw_relation = relationId;
+	workitem->avw_blockNumber = blkno;
+	workitem->avw_active = false;
+
+	/* ... and put it on autovacuum's to-do list */
+	add_wi_to_list(&workitems->avs_usedItems, wi_ptr);
+
+	LWLockRelease(AutovacuumLock);
+
+	dsa_detach(AutoVacuumDSA);
+	AutoVacuumDSA = NULL;
+}
+
+/*
  * autovac_init
  *		This is called at postmaster initialization.
  *
@@ -3079,3 +3451,59 @@ autovac_refresh_stats(void)
 
 	pgstat_clear_snapshot();
 }
+
+/*
+ * Simplistic open-coded list implementation for objects stored in DSA.
+ * Each item is doubly linked, but we have no tail pointer, and the "prev"
+ * element of the first item is null, not the list.
+ */
+
+/*
+ * Remove a work item from the given list.
+ */
+static void
+remove_wi_from_list(dsa_pointer *list, dsa_pointer wi_ptr)
+{
+	AutoVacuumWorkItem *workitem = dsa_get_address(AutoVacuumDSA, wi_ptr);
+	dsa_pointer		next = workitem->avw_next;
+	dsa_pointer		prev = workitem->avw_prev;
+
+	workitem->avw_next = workitem->avw_prev = InvalidDsaPointer;
+
+	if (next != InvalidDsaPointer)
+	{
+		workitem = dsa_get_address(AutoVacuumDSA, next);
+		workitem->avw_prev = prev;
+	}
+
+	if (prev != InvalidDsaPointer)
+	{
+		workitem = dsa_get_address(AutoVacuumDSA, prev);
+		workitem->avw_next = next;
+	}
+	else
+		*list = next;
+}
+
+/*
+ * Add a workitem to the given list
+ */
+static void
+add_wi_to_list(dsa_pointer *list, dsa_pointer wi_ptr)
+{
+	if (*list == InvalidDsaPointer)
+	{
+		/* list is empty; item is now singleton */
+		*list = wi_ptr;
+	}
+	else
+	{
+		AutoVacuumWorkItem *workitem = dsa_get_address(AutoVacuumDSA, wi_ptr);
+		AutoVacuumWorkItem *old = dsa_get_address(AutoVacuumDSA, *list);
+
+		/* Put item at head of list */
+		workitem->avw_next = *list;
+		old->avw_prev = wi_ptr;
+		*list = wi_ptr;
+	}
+}
diff --git a/src/backend/storage/lmgr/lwlock.c b/src/backend/storage/lmgr/lwlock.c
index 3e13394..c4313a5 100644
--- a/src/backend/storage/lmgr/lwlock.c
+++ b/src/backend/storage/lmgr/lwlock.c
@@ -494,7 +494,7 @@ RegisterLWLockTranches(void)
 
 	if (LWLockTrancheArray == NULL)
 	{
-		LWLockTranchesAllocated = 64;
+		LWLockTranchesAllocated = 72;
 		LWLockTrancheArray = (char **)
 			MemoryContextAllocZero(TopMemoryContext,
 						  LWLockTranchesAllocated * sizeof(char *));
diff --git a/src/include/access/brin.h b/src/include/access/brin.h
index 896824a..3f4c29b 100644
--- a/src/include/access/brin.h
+++ b/src/include/access/brin.h
@@ -22,6 +22,7 @@ typedef struct BrinOptions
 {
 	int32		vl_len_;		/* varlena header (do not touch directly!) */
 	BlockNumber pagesPerRange;
+	bool		autosummarize;
 } BrinOptions;
 
 #define BRIN_DEFAULT_PAGES_PER_RANGE	128
@@ -29,5 +30,9 @@ typedef struct BrinOptions
 	((relation)->rd_options ? \
 	 ((BrinOptions *) (relation)->rd_options)->pagesPerRange : \
 	  BRIN_DEFAULT_PAGES_PER_RANGE)
+#define BrinGetAutoSummarize(relation) \
+	((relation)->rd_options ? \
+	 ((BrinOptions *) (relation)->rd_options)->autosummarize : \
+	  false)
 
 #endif   /* BRIN_H */
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index 1132a60..1b7ab2a 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -564,6 +564,8 @@ DATA(insert OID = 335 (  brinhandler	PGNSP PGUID 12 1 0 0 0 f f f f t f v s 1 0
 DESCR("brin index access method handler");
 DATA(insert OID = 3952 (  brin_summarize_new_values PGNSP PGUID 12 1 0 0 0 f f f f t f v s 1 0 23 "2205" _null_ _null_ _null_ _null_ _null_ brin_summarize_new_values _null_ _null_ _null_ ));
 DESCR("brin: standalone scan new table pages");
+DATA(insert OID = 3999 (  brin_summarize_range PGNSP PGUID 12 1 0 0 0 f f f f t f v s 2 0 23 "2205 20" _null_ _null_ _null_ _null_ _null_ brin_summarize_range _null_ _null_ _null_ ));
+DESCR("brin: standalone scan new table pages");
 
 DATA(insert OID = 338 (  amvalidate		PGNSP PGUID 12 1 0 0 0 f f f f t f v s 1 0 16 "26" _null_ _null_ _null_ _null_ _null_	amvalidate _null_ _null_ _null_ ));
 DESCR("validate an operator class");
diff --git a/src/include/postmaster/autovacuum.h b/src/include/postmaster/autovacuum.h
index 99d7f09..174e91a 100644
--- a/src/include/postmaster/autovacuum.h
+++ b/src/include/postmaster/autovacuum.h
@@ -14,6 +14,15 @@
 #ifndef AUTOVACUUM_H
 #define AUTOVACUUM_H
 
+/*
+ * Other processes can request specific work from autovacuum, identified by
+ * AutoVacuumWorkItem elements.
+ */
+typedef enum
+{
+	AVW_BRINSummarizeRange
+} AutoVacuumWorkItemType;
+
 
 /* GUC variables */
 extern bool autovacuum_start_daemon;
@@ -60,6 +69,9 @@ extern void AutovacuumWorkerIAm(void);
 extern void AutovacuumLauncherIAm(void);
 #endif
 
+extern void AutoVacuumRequestWork(AutoVacuumWorkItemType type,
+					  Oid relationId, BlockNumber blkno);
+
 /* shared memory stuff */
 extern Size AutoVacuumShmemSize(void);
 extern void AutoVacuumShmemInit(void);
diff --git a/src/include/storage/lwlock.h b/src/include/storage/lwlock.h
index 0cd45bb..9105f3d 100644
--- a/src/include/storage/lwlock.h
+++ b/src/include/storage/lwlock.h
@@ -211,6 +211,7 @@ typedef enum BuiltinTrancheIds
 	LWTRANCHE_BUFFER_MAPPING,
 	LWTRANCHE_LOCK_MANAGER,
 	LWTRANCHE_PREDICATE_LOCK_MANAGER,
+	LWTRANCHE_AUTOVACUUM,
 	LWTRANCHE_PARALLEL_QUERY_DSA,
 	LWTRANCHE_TBM,
 	LWTRANCHE_FIRST_USER_DEFINED

*** /home/jjanes/pgsql/git/src/test/regress/expected/brin.out	Sat Apr  1 11:53:51 2017
--- /home/jjanes/pgsql/git/src/test/regress/results/brin.out	Sat Apr  1 11:54:41 2017
***************
*** 425,431 ****
  SELECT brin_summarize_range('brin_summarize_idx', 0);
   brin_summarize_range 
  ----------------------
!                     1
  (1 row)
  
  -- nothing: already summarized
--- 425,431 ----
  SELECT brin_summarize_range('brin_summarize_idx', 0);
   brin_summarize_range 
  ----------------------
!                     0
  (1 row)
  
  -- nothing: already summarized

======================================================================