Subject: [PATCH v28 5/7] Shared-memory based stats collector

From: Kyotaro Horiguchi <[email-masked]>
Date: Thu, 19 Mar 2020 15:11:14 +0900

Previously activity statistics is collected via sockets and shared
among backends through files periodically. Such files reaches tens of
megabytes and are created at most every 500ms and such large data is
serialized by stats collector then de-serialized on every backend
periodically. To evade that large cost, this patch places activity
statistics data on shared memory. Each backend accumulates statistics
numbers locally then tries to move them onto the shared statistics at
every transaction end but with intervals not shorter than 500ms. Locks
on the shared statistics is acquired by the units of such like tables,
functions so the expected chance of collision are not so
high. Furthermore, until 1 second has elapsed since the last flushing
to shared stats, lock failure postpones stats flushing so that lock
contention doesn't slow down transactions.  Finally stats flush waits
for locks so that shared statistics doesn't get stale.
---
 src/backend/access/transam/xlog.c            |    4 +-
 src/backend/catalog/index.c                  |   24 +-
 src/backend/postmaster/autovacuum.c          |   54 +-
 src/backend/postmaster/bgwriter.c            |    2 +-
 src/backend/postmaster/checkpointer.c        |   12 +-
 src/backend/postmaster/pgarch.c              |    4 +-
 src/backend/postmaster/pgstat.c              | 4864 +++++++-----------
 src/backend/postmaster/postmaster.c          |   85 +-
 src/backend/storage/buffer/bufmgr.c          |    8 +-
 src/backend/storage/ipc/ipci.c               |    2 +
 src/backend/storage/lmgr/lwlock.c            |    1 +
 src/backend/storage/lmgr/lwlocknames.txt     |    1 +
 src/backend/tcop/postgres.c                  |   26 +-
 src/backend/utils/adt/pgstatfuncs.c          |   53 +-
 src/backend/utils/init/globals.c             |    1 +
 src/backend/utils/init/postinit.c            |   11 +
 src/bin/pg_basebackup/t/010_pg_basebackup.pl |    4 +-
 src/include/miscadmin.h                      |    2 +
 src/include/pgstat.h                         |  514 +-
 src/include/storage/lwlock.h                 |    1 +
 src/include/utils/timeout.h                  |    1 +
 21 files changed, 2062 insertions(+), 3612 deletions(-)

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 5e663699d5..749c2e8adb 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -8530,9 +8530,9 @@ LogCheckpointEnd(bool restartpoint)
 						&sync_secs, &sync_usecs);
 
 	/* Accumulate checkpoint timing summary data, in milliseconds. */
-	BgWriterStats.m_checkpoint_write_time +=
+	BgWriterStats.checkpoint_write_time +=
 		write_secs * 1000 + write_usecs / 1000;
-	BgWriterStats.m_checkpoint_sync_time +=
+	BgWriterStats.checkpoint_sync_time +=
 		sync_secs * 1000 + sync_usecs / 1000;
 
 	/*
diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c
index 2d81bc3cbc..4de574ae00 100644
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -1687,28 +1687,10 @@ index_concurrently_swap(Oid newIndexId, Oid oldIndexId, const char *oldName)
 
 	/*
 	 * Copy over statistics from old to new index
+	 * The data will be sent by the next pgstat_report_stat()
+	 * call.
 	 */
-	{
-		PgStat_StatTabEntry *tabentry;
-
-		tabentry = pgstat_fetch_stat_tabentry(oldIndexId);
-		if (tabentry)
-		{
-			if (newClassRel->pgstat_info)
-			{
-				newClassRel->pgstat_info->t_counts.t_numscans = tabentry->numscans;
-				newClassRel->pgstat_info->t_counts.t_tuples_returned = tabentry->tuples_returned;
-				newClassRel->pgstat_info->t_counts.t_tuples_fetched = tabentry->tuples_fetched;
-				newClassRel->pgstat_info->t_counts.t_blocks_fetched = tabentry->blocks_fetched;
-				newClassRel->pgstat_info->t_counts.t_blocks_hit = tabentry->blocks_hit;
-
-				/*
-				 * The data will be sent by the next pgstat_report_stat()
-				 * call.
-				 */
-			}
-		}
-	}
+	pgstat_copy_index_counters(oldIndexId, newClassRel->pgstat_info);
 
 	/* Close relations */
 	table_close(pg_class, RowExclusiveLock);
diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index 7e97ffab27..800693af4a 100644
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -338,9 +338,6 @@ static void autovacuum_do_vac_analyze(autovac_table *tab,
 									  BufferAccessStrategy bstrategy);
 static AutoVacOpts *extract_autovac_opts(HeapTuple tup,
 										 TupleDesc pg_class_desc);
-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,
@@ -1938,8 +1935,6 @@ do_autovacuum(void)
 	HASHCTL		ctl;
 	HTAB	   *table_toast_map;
 	ListCell   *volatile cell;
-	PgStat_StatDBEntry *shared;
-	PgStat_StatDBEntry *dbentry;
 	BufferAccessStrategy bstrategy;
 	ScanKeyData key;
 	TupleDesc	pg_class_desc;
@@ -1958,12 +1953,6 @@ do_autovacuum(void)
 										  ALLOCSET_DEFAULT_SIZES);
 	MemoryContextSwitchTo(AutovacMemCxt);
 
-	/*
-	 * may be NULL if we couldn't find an entry (only happens if we are
-	 * forcing a vacuum for anti-wrap purposes).
-	 */
-	dbentry = pgstat_fetch_stat_dbentry(MyDatabaseId);
-
 	/* Start a transaction so our commands have one to play into. */
 	StartTransactionCommand();
 
@@ -2011,9 +2000,6 @@ do_autovacuum(void)
 	/* StartTransactionCommand changed elsewhere */
 	MemoryContextSwitchTo(AutovacMemCxt);
 
-	/* The database hash where pgstat keeps shared relations */
-	shared = pgstat_fetch_stat_dbentry(InvalidOid);
-
 	classRel = table_open(RelationRelationId, AccessShareLock);
 
 	/* create a copy so we can use it after closing pg_class */
@@ -2092,8 +2078,8 @@ do_autovacuum(void)
 
 		/* Fetch reloptions and the pgstat entry for this table */
 		relopts = extract_autovac_opts(tuple, pg_class_desc);
-		tabentry = get_pgstat_tabentry_relid(relid, classForm->relisshared,
-											 shared, dbentry);
+		tabentry = pgstat_fetch_stat_tabentry_snapshot(classForm->relisshared,
+													   relid);
 
 		/* Check if it needs vacuum or analyze */
 		relation_needs_vacanalyze(relid, relopts, classForm, tabentry,
@@ -2176,8 +2162,8 @@ do_autovacuum(void)
 		}
 
 		/* Fetch the pgstat entry for this table */
-		tabentry = get_pgstat_tabentry_relid(relid, classForm->relisshared,
-											 shared, dbentry);
+		tabentry = pgstat_fetch_stat_tabentry_snapshot(classForm->relisshared,
+													   relid);
 
 		relation_needs_vacanalyze(relid, relopts, classForm, tabentry,
 								  effective_multixact_freeze_max_age,
@@ -2736,29 +2722,6 @@ extract_autovac_opts(HeapTuple tup, TupleDesc pg_class_desc)
 	return av;
 }
 
-/*
- * get_pgstat_tabentry_relid
- *
- * Fetch the pgstat entry of a table, either local to a database or shared.
- */
-static PgStat_StatTabEntry *
-get_pgstat_tabentry_relid(Oid relid, bool isshared, PgStat_StatDBEntry *shared,
-						  PgStat_StatDBEntry *dbentry)
-{
-	PgStat_StatTabEntry *tabentry = NULL;
-
-	if (isshared)
-	{
-		if (PointerIsValid(shared))
-			tabentry = hash_search(shared->tables, &relid,
-								   HASH_FIND, NULL);
-	}
-	else if (PointerIsValid(dbentry))
-		tabentry = hash_search(dbentry->tables, &relid,
-							   HASH_FIND, NULL);
-
-	return tabentry;
-}
 
 /*
  * table_recheck_autovac
@@ -2779,17 +2742,12 @@ table_recheck_autovac(Oid relid, HTAB *table_toast_map,
 	bool		doanalyze;
 	autovac_table *tab = NULL;
 	PgStat_StatTabEntry *tabentry;
-	PgStat_StatDBEntry *shared;
-	PgStat_StatDBEntry *dbentry;
 	bool		wraparound;
 	AutoVacOpts *avopts;
 
 	/* use fresh stats */
 	autovac_refresh_stats();
 
-	shared = pgstat_fetch_stat_dbentry(InvalidOid);
-	dbentry = pgstat_fetch_stat_dbentry(MyDatabaseId);
-
 	/* fetch the relation's relcache entry */
 	classTup = SearchSysCacheCopy1(RELOID, ObjectIdGetDatum(relid));
 	if (!HeapTupleIsValid(classTup))
@@ -2813,8 +2771,8 @@ table_recheck_autovac(Oid relid, HTAB *table_toast_map,
 	}
 
 	/* fetch the pgstat table entry */
-	tabentry = get_pgstat_tabentry_relid(relid, classForm->relisshared,
-										 shared, dbentry);
+	tabentry = pgstat_fetch_stat_tabentry_snapshot(classForm->relisshared,
+												   relid);
 
 	relation_needs_vacanalyze(relid, avopts, classForm, tabentry,
 							  effective_multixact_freeze_max_age,
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index 069e27e427..94bdd664b5 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -236,7 +236,7 @@ BackgroundWriterMain(void)
 		/*
 		 * Send off activity statistics to the stats collector
 		 */
-		pgstat_send_bgwriter();
+		pgstat_report_bgwriter();
 
 		if (FirstCallSinceLastCheckpoint())
 		{
diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c
index e354a78725..8a2fd0ddb2 100644
--- a/src/backend/postmaster/checkpointer.c
+++ b/src/backend/postmaster/checkpointer.c
@@ -350,7 +350,7 @@ CheckpointerMain(void)
 		if (((volatile CheckpointerShmemStruct *) CheckpointerShmem)->ckpt_flags)
 		{
 			do_checkpoint = true;
-			BgWriterStats.m_requested_checkpoints++;
+			BgWriterStats.requested_checkpoints++;
 		}
 
 		/*
@@ -364,7 +364,7 @@ CheckpointerMain(void)
 		if (elapsed_secs >= CheckPointTimeout)
 		{
 			if (!do_checkpoint)
-				BgWriterStats.m_timed_checkpoints++;
+				BgWriterStats.timed_checkpoints++;
 			do_checkpoint = true;
 			flags |= CHECKPOINT_CAUSE_TIME;
 		}
@@ -492,7 +492,7 @@ CheckpointerMain(void)
 		 * worth the trouble to split the stats support into two independent
 		 * stats message types.)
 		 */
-		pgstat_send_bgwriter();
+		pgstat_report_bgwriter();
 
 		/*
 		 * Sleep until we are signaled or it's time for another checkpoint or
@@ -693,7 +693,7 @@ CheckpointWriteDelay(int flags, double progress)
 		/*
 		 * Report interim activity statistics to the stats collector.
 		 */
-		pgstat_send_bgwriter();
+		pgstat_report_bgwriter();
 
 		/*
 		 * This sleep used to be connected to bgwriter_delay, typically 200ms.
@@ -1238,8 +1238,8 @@ AbsorbSyncRequests(void)
 	LWLockAcquire(CheckpointerCommLock, LW_EXCLUSIVE);
 
 	/* Transfer stats counts into pending pgstats message */
-	BgWriterStats.m_buf_written_backend += CheckpointerShmem->num_backend_writes;
-	BgWriterStats.m_buf_fsync_backend += CheckpointerShmem->num_backend_fsync;
+	BgWriterStats.buf_written_backend += CheckpointerShmem->num_backend_writes;
+	BgWriterStats.buf_fsync_backend += CheckpointerShmem->num_backend_fsync;
 
 	CheckpointerShmem->num_backend_writes = 0;
 	CheckpointerShmem->num_backend_fsync = 0;
diff --git a/src/backend/postmaster/pgarch.c b/src/backend/postmaster/pgarch.c
index 6fe7a136ba..f0b524ca50 100644
--- a/src/backend/postmaster/pgarch.c
+++ b/src/backend/postmaster/pgarch.c
@@ -401,7 +401,7 @@ pgarch_ArchiverCopyLoop(void)
 				 * Tell the collector about the WAL file that we successfully
 				 * archived
 				 */
-				pgstat_send_archiver(xlog, false);
+				pgstat_report_archiver(xlog, false);
 
 				break;			/* out of inner retry loop */
 			}
@@ -411,7 +411,7 @@ pgarch_ArchiverCopyLoop(void)
 				 * Tell the collector about the WAL file that we failed to
 				 * archive
 				 */
-				pgstat_send_archiver(xlog, true);
+				pgstat_report_archiver(xlog, true);
 
 				if (++failures >= NUM_ARCHIVE_RETRIES)
 				{
diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index ab42df7e1b..8c65df9bfd 100644
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -1,15 +1,22 @@
 /* ----------
  * pgstat.c
  *
- *	All the statistics collector stuff hacked up in one big, ugly file.
+ *	Activity Statistics facility.
  *
- *	TODO:	- Separate collector, postmaster and backend stuff
- *			  into different files.
+ *  Collects activity statistics, e.g. per-table access statistics, of
+ *  all backends in shared memory. The activity numbers are first stored
+ *  locally in each process, then flushed to shared memory at commit
+ *  time or by idle-timeout.
  *
- *			- Add some automatic call for pgstat vacuuming.
+ * To avoid congestion on the shared memory, shared stats is updated no more
+ * often than once per PGSTAT_MIN_INTERVAL (1000ms). If some local numbers
+ * remain unflushed for lock failure, retry with intervals that is initially
+ * PGSTAT_RETRY_MIN_INTERVAL (250ms) then doubled at every retry. Finally we
+ * force update after PGSTAT_MAX_INTERVAL (10000ms) since the first trial.
  *
- *			- Add a pgstat config column to pg_database, so this
- *			  entire thing can be enabled/disabled on a per db basis.
+ *  The first process that uses activity statistics facility creates the area
+ *  then load the stored stats file if any, and the last process at shutdown
+ *  writes the shared stats to the file then destroy the area before exit.
  *
  *	Copyright (c) 2001-2020, PostgreSQL Global Development Group
  *
@@ -19,18 +26,6 @@
 #include "postgres.h"
 
 #include <unistd.h>
-#include <fcntl.h>
-#include <sys/param.h>
-#include <sys/time.h>
-#include <sys/socket.h>
-#include <netdb.h>
-#include <netinet/in.h>
-#include <arpa/inet.h>
-#include <signal.h>
-#include <time.h>
-#ifdef HAVE_SYS_SELECT_H
-#include <sys/select.h>
-#endif
 
 #include "access/heapam.h"
 #include "access/htup_details.h"
@@ -40,68 +35,43 @@
 #include "access/xact.h"
 #include "catalog/pg_database.h"
 #include "catalog/pg_proc.h"
-#include "common/ip.h"
 #include "libpq/libpq.h"
-#include "libpq/pqsignal.h"
-#include "mb/pg_wchar.h"
 #include "miscadmin.h"
-#include "pg_trace.h"
 #include "pgstat.h"
 #include "postmaster/autovacuum.h"
 #include "postmaster/fork_process.h"
 #include "postmaster/interrupt.h"
 #include "postmaster/postmaster.h"
 #include "replication/walsender.h"
-#include "storage/backendid.h"
-#include "storage/dsm.h"
-#include "storage/fd.h"
 #include "storage/ipc.h"
-#include "storage/latch.h"
 #include "storage/lmgr.h"
-#include "storage/pg_shmem.h"
+#include "storage/proc.h"
 #include "storage/procsignal.h"
 #include "storage/sinvaladt.h"
 #include "utils/ascii.h"
 #include "utils/guc.h"
 #include "utils/memutils.h"
-#include "utils/ps_status.h"
-#include "utils/rel.h"
+#include "utils/probes.h"
 #include "utils/snapmgr.h"
-#include "utils/timestamp.h"
 
 /* ----------
  * Timer definitions.
  * ----------
  */
-#define PGSTAT_STAT_INTERVAL	500 /* Minimum time between stats file
-									 * updates; in milliseconds. */
+#define PGSTAT_MIN_INTERVAL			1000	/* Minimum interval of stats data
+											 * updates; in milliseconds. */
 
-#define PGSTAT_RETRY_DELAY		10	/* How long to wait between checks for a
-									 * new file; in milliseconds. */
-
-#define PGSTAT_MAX_WAIT_TIME	10000	/* Maximum time to wait for a stats
-										 * file update; in milliseconds. */
-
-#define PGSTAT_INQ_INTERVAL		640 /* How often to ping the collector for a
-									 * new file; in milliseconds. */
-
-#define PGSTAT_RESTART_INTERVAL 60	/* How often to attempt to restart a
-									 * failed statistics collector; in
-									 * seconds. */
-
-#define PGSTAT_POLL_LOOP_COUNT	(PGSTAT_MAX_WAIT_TIME / PGSTAT_RETRY_DELAY)
-#define PGSTAT_INQ_LOOP_COUNT	(PGSTAT_INQ_INTERVAL / PGSTAT_RETRY_DELAY)
-
-/* Minimum receive buffer size for the collector's socket. */
-#define PGSTAT_MIN_RCVBUF		(100 * 1024)
+#define PGSTAT_RETRY_MIN_INTERVAL	250 /* Initial retry interval after
+										 * PGSTAT_MIN_INTERVAL */
 
+#define PGSTAT_MAX_INTERVAL			10000	/* Longest interval of stats data
+											 * updates */
 
 /* ----------
- * The initial size hints for the hash tables used in the collector.
+ * The initial size hints for the hash tables used in the activity statistics.
  * ----------
  */
-#define PGSTAT_DB_HASH_SIZE		16
-#define PGSTAT_TAB_HASH_SIZE	512
+#define PGSTAT_TABLE_HASH_SIZE	512
 #define PGSTAT_FUNCTION_HASH_SIZE	512

@@ -116,7 +86,6 @@
  */
 #define NumBackendStatSlots (MaxBackends + NUM_AUXPROCTYPES)
 
-
 /* ----------
  * GUC parameters
  * ----------
@@ -131,75 +100,162 @@ int			pgstat_track_activity_query_size = 1024;
  * ----------
  */
 char	   *pgstat_stat_directory = NULL;
+
+/* No longer used, but will be removed with GUC */
 char	   *pgstat_stat_filename = NULL;
 char	   *pgstat_stat_tmpname = NULL;
 
 /*
- * BgWriter global statistics counters (unused in other processes).
- * Stored directly in a stats message structure so it can be sent
- * without needing to copy things around.  We assume this inits to zeroes.
- */
-PgStat_MsgBgWriter BgWriterStats;
-
-/* ----------
- * Local data
- * ----------
+ * Shared stats bootstrap information, protected by StatsLock.
+ *
+ * refcount is used to know whether a process going to detach shared stats is
+ * the last process or not. The last process writes out the stats files.
  */
-NON_EXEC_STATIC pgsocket pgStatSock = PGINVALID_SOCKET;
-
-static struct sockaddr_storage pgStatAddr;
+typedef struct StatsShmemStruct
+{
+	dsa_handle	stats_dsa_handle;	/* handle for stats data area */
+	dshash_table_handle hash_handle;	/* shared dbstat hash */
+	dsa_pointer global_stats;	/* DSA pointer to global stats */
+	dsa_pointer archiver_stats; /* Ditto for archiver stats */
+	int			refcount;		/* # of processes that is attaching the shared
+								 * stats memory */
+}			StatsShmemStruct;
 
-static time_t last_pgstat_start_time;
+/* BgWriter global statistics counters */
+PgStat_BgWriter BgWriterStats = {0};
 
-static bool pgStatRunningInCollector = false;
+/* backend-lifetime storages */
+static StatsShmemStruct * StatsShmem = NULL;
+static dsa_area *area = NULL;
 
 /*
- * Structures in which backends store per-table info that's waiting to be
- * sent to the collector.
+ * Enums and types to define shared statistics structure.
+ *
+ * Statistics entries for each object is stored in individual DSA-allocated
+ * memory. Every entry is pointed from the dshash pgStatSharedHash via
+ * dsa_pointer. The structure makes object-stats entries not moved by dshash
+ * resizing, and allows the dshash can release lock sooner on stats
+ * updates. Also it reduces interfering among write-locks on each stat entry by
+ * not relying on partition lock of dshash. pgStatLocalHashEntry is the equivalent of pgStatSharedHash for local stat entries.
+ *
+ * Each stat entry is enveloped by the type PgStatEnvelope, which stores common
+ * attribute of all kind of statistics and a LWLock lock object.
  *
- * NOTE: once allocated, TabStatusArray structures are never moved or deleted
- * for the life of the backend.  Also, we zero out the t_id fields of the
- * contained PgStat_TableStatus structs whenever they are not actively in use.
- * This allows relcache pgstat_info pointers to be treated as long-lived data,
- * avoiding repeated searches in pgstat_initstats() when a relation is
- * repeatedly opened during a transaction.
+ * Shared stats are stored as:
+ *
+ * dshash pgStatSharedHash
+ *    -> PgStatHashEntry				(dshash entry)
+ *      (dsa_pointer)-> PgStatEnvelope	(dsa memory block)
+ *
+ * Local stats are stored as:
+ *
+ * dshash pgStatLocalHash
+ *    -> PgStatLocalHashEntry			(dynahash entry)
+ *      (direct pointer)-> PgStatEnvelope (palloc'ed memory)
  */
-#define TABSTAT_QUANTUM		100 /* we alloc this many at a time */
 
-typedef struct TabStatusArray
+/* The types of statistics entries. */
+typedef enum PgStatTypes
 {
-	struct TabStatusArray *tsa_next;	/* link to next array, if any */
-	int			tsa_used;		/* # entries currently used */
-	PgStat_TableStatus tsa_entries[TABSTAT_QUANTUM];	/* per-table data */
-} TabStatusArray;
-
-static TabStatusArray *pgStatTabList = NULL;
+	PGSTAT_TYPE_ALL,			/* Not a type, for the parameters of
+								 * pgstat_collect_stat_entries */
+	PGSTAT_TYPE_DB,				/* database-wide statistics */
+	PGSTAT_TYPE_TABLE,			/* per-table statistics */
+	PGSTAT_TYPE_FUNCTION,		/* per-function statistics */
+}			PgStatTypes;
 
 /*
- * pgStatTabHash entry: map from relation OID to PgStat_TableStatus pointer
+ * entry size lookup table of shared statistics entries corresponding to
+ * PgStatTypes
  */
-typedef struct TabStatHashEntry
+static size_t pgstat_entsize[] =
 {
-	Oid			t_id;
-	PgStat_TableStatus *tsa_entry;
-} TabStatHashEntry;
+	0,							/* PGSTAT_TYPE_ALL: not an entry */
+	sizeof(PgStat_StatDBEntry), /* PGSTAT_TYPE_DB */
+	sizeof(PgStat_StatTabEntry),	/* PGSTAT_TYPE_TABLE */
+	sizeof(PgStat_StatFuncEntry)	/* PGSTAT_TYPE_FUNCTION */
+};
 
-/*
- * Hash table for O(1) t_id -> tsa_entry lookup
- */
-static HTAB *pgStatTabHash = NULL;
+/* Ditto for local statistics entries */
+static size_t pgstat_localentsize[] =
+{
+	0,							/* PGSTAT_TYPE_ALL: not an entry */
+	sizeof(PgStat_StatDBEntry), /* PGSTAT_TYPE_DB */
+	sizeof(PgStat_TableStatus), /* PGSTAT_TYPE_TABLE */
+	sizeof(PgStat_BackendFunctionEntry) /* PGSTAT_TYPE_FUNCTION */
+};
+
+/* struct for shared statistics hash entry key. */
+typedef struct PgStatHashEntryKey
+{
+	PgStatTypes type;			/* statistics entry type */
+	Oid			databaseid;		/* database ID. InvalidOid for shared objects. */
+	Oid			objectid;		/* object OID */
+}			PgStatHashEntryKey;
 
 /*
- * Backends store per-function info that's waiting to be sent to the collector
- * in this hash table (indexed by function OID).
+ * Stats numbers that are waiting for flushing out to shared stats are held in
+ * pgStatLocalHash,
  */
-static HTAB *pgStatFunctions = NULL;
+typedef struct PgStatHashEntry
+{
+	PgStatHashEntryKey key;		/* hash key */
+	dsa_pointer env;			/* pointer to shared stats envelope in DSA */
+}			PgStatHashEntry;
+
+/* struct for shared statistics entry pointed from shared hash entry. */
+typedef struct PgStatEnvelope
+{
+	PgStatTypes type;			/* statistics entry type */
+	Oid			databaseid;		/* databaseid */
+	Oid			objectid;		/* objectid */
+	size_t		len;			/* length of body, fixed per type. */
+	LWLock		lock;			/* lightweight lock to protect body */
+	int			body[FLEXIBLE_ARRAY_MEMBER];	/* statistics body */
+}			PgStatEnvelope;
+
+#define PgStatEnvelopeSize(bodylen) \
+	(offsetof(PgStatEnvelope, body) + (bodylen))
+
+/* struct for shared statistics local hash entry. */
+typedef struct PgStatLocalHashEntry
+{
+	PgStatHashEntryKey key;		/* hash key */
+	PgStatEnvelope *env;		/* pointer to stats envelope in heap */
+}			PgStatLocalHashEntry;
 
 /*
- * Indicates if backend has some function stats that it hasn't yet
- * sent to the collector.
+ * Snapshot is stats entry that is locally copied to offset stable values for a
+ * transaction.
  */
-static bool have_function_stats = false;
+typedef struct PgStatSnapshot
+{
+	PgStatHashEntryKey key;
+	bool		negative;
+	int			body[FLEXIBLE_ARRAY_MEMBER];	/* statistics body */
+}			PgStatSnapshot;
+
+#define PgStatSnapshotSize(bodylen)				\
+	(offsetof(PgStatSnapshot, body) + (bodylen))
+
+/* parameter for shared hashes */
+static const dshash_parameters dsh_rootparams = {
+	sizeof(PgStatHashEntryKey),
+	sizeof(PgStatHashEntry),
+	dshash_memcmp,
+	dshash_memhash,
+	LWTRANCHE_STATS
+};
+
+/* The shared hash to index activity stats entries. */
+static dshash_table *pgStatSharedHash = NULL;
+
+/* Local stats numbers are stored here */
+static HTAB *pgStatLocalHash = NULL;
+
+#define HAVE_ANY_PENDING_STATS()						\
+	(pgStatLocalHash != NULL ||							\
+	 pgStatXactCommit != 0 || pgStatXactRollback != 0)
 
 /*
  * Tuple insertion/deletion counts for an open transaction can't be propagated
@@ -236,11 +292,10 @@ typedef struct TwoPhasePgStatRecord
 	bool		t_truncated;	/* was the relation truncated? */
 } TwoPhasePgStatRecord;
 
-/*
- * Info about current "snapshot" of stats file
- */
+/* Variables for backend status snapshot */
 static MemoryContext pgStatLocalContext = NULL;
-static HTAB *pgStatDBHash = NULL;
+static MemoryContext pgStatSnapshotContext = NULL;
+static HTAB *pgStatSnapshotHash = NULL;
 
 /* Status for backends including auxiliary */
 static LocalPgBackendStatus *localBackendStatusTable = NULL;
@@ -249,19 +304,17 @@ static LocalPgBackendStatus *localBackendStatusTable = NULL;
 static int	localNumBackends = 0;
 
 /*
- * Cluster wide statistics, kept in the stats collector.
- * Contains statistics that are not collected per database
- * or per table.
+ * Cluster wide statistics.
+ *
+ * Contains statistics that are collected not per database nor per table
+ * basis.  shared_* points to shared memory and snapshot_* are backend
+ * snapshots.
  */
-static PgStat_ArchiverStats archiverStats;
-static PgStat_GlobalStats globalStats;
-
-/*
- * List of OIDs of databases we need to write out.  If an entry is InvalidOid,
- * it means to write only the shared-catalog stats ("DB 0"); otherwise, we
- * will write both that DB's data and the shared stats.
- */
-static List *pending_write_requests = NIL;
+static bool global_snapshot_is_valid = false;
+static PgStat_ArchiverStats *shared_archiverStats;
+static PgStat_ArchiverStats snapshot_archiverStats;
+static PgStat_GlobalStats *shared_globalStats;
+static PgStat_GlobalStats snapshot_globalStats;
 
 /*
  * Total time charged to functions so far in the current backend.
@@ -270,523 +323,269 @@ static List *pending_write_requests = NIL;
  */
 static instr_time total_func_time;
 
+/*
+ * Newly created shared stats entries needs to be initialized before the other
+ * processes get access it. get_stat_entry() calls it for the purpose.
+ */
+typedef void (*entry_initializer) (PgStatEnvelope * env);
 
 /* ----------
  * Local function forward declarations
  * ----------
  */
-#ifdef EXEC_BACKEND
-static pid_t pgstat_forkexec(void);
-#endif
-
-NON_EXEC_STATIC void PgstatCollectorMain(int argc, char *argv[]) pg_attribute_noreturn();
 static void pgstat_beshutdown_hook(int code, Datum arg);
 
-static PgStat_StatDBEntry *pgstat_get_db_entry(Oid databaseid, bool create);
-static PgStat_StatTabEntry *pgstat_get_tab_entry(PgStat_StatDBEntry *dbentry,
-												 Oid tableoid, bool create);
-static void pgstat_write_statsfiles(bool permanent, bool allDbs);
-static void pgstat_write_db_statsfile(PgStat_StatDBEntry *dbentry, bool permanent);
-static HTAB *pgstat_read_statsfiles(Oid onlydb, bool permanent, bool deep);
-static void pgstat_read_db_statsfile(Oid databaseid, HTAB *tabhash, HTAB *funchash, bool permanent);
-static void backend_read_statsfile(void);
+static PgStatEnvelope * get_stat_entry(PgStatTypes type, Oid dbid, Oid objid,
+									   bool nowait,
+									   entry_initializer initfunc, bool *found);
+static PgStatEnvelope * *collect_stat_entries(PgStatTypes type, Oid dbid);
+static void create_missing_dbentries(void);
+static void pgstat_write_database_stats(PgStat_StatDBEntry *dbentry);
+static void pgstat_read_db_statsfile(PgStat_StatDBEntry *dbentry);
+
+static bool flush_tabstat(PgStatEnvelope * env, bool nowait);
+static bool flush_funcstat(PgStatEnvelope * env, bool nowait);
+static bool flush_dbstat(PgStatEnvelope * env, bool nowait);
+
+static void init_dbentry(PgStatEnvelope * env);
+static void init_funcentry(PgStatEnvelope * env);
+static void init_tabentry(PgStatEnvelope * env);
+
+static bool delete_stat_entry(PgStatTypes type, Oid dbid, Oid objid,
+							  bool nowait);
+static PgStatEnvelope * get_local_stat_entry(PgStatTypes type, Oid dbid, Oid objid,
+											 bool create, bool *found);
+static PgStat_StatDBEntry *get_local_dbstat_entry(Oid dbid);
+static PgStat_TableStatus *get_local_tabstat_entry(Oid rel_id, bool isshared);
+
+static PgStat_SubXactStatus *get_tabstat_stack_level(int nest_level);
+static void add_tabstat_xact_level(PgStat_TableStatus *pgstat_info, int nest_level);
+static void pgstat_snapshot_global_stats(void);
+
 static void pgstat_read_current_status(void);
-
-static bool pgstat_write_statsfile_needed(void);
-static bool pgstat_db_requested(Oid databaseid);
-
-static void pgstat_send_tabstat(PgStat_MsgTabstat *tsmsg);
-static void pgstat_send_funcstats(void);
-static HTAB *pgstat_collect_oids(Oid catalogid, AttrNumber anum_oid);
-
-static PgStat_TableStatus *get_tabstat_entry(Oid rel_id, bool isshared);
-
-static void pgstat_setup_memcxt(void);
-
 static const char *pgstat_get_wait_activity(WaitEventActivity w);
 static const char *pgstat_get_wait_client(WaitEventClient w);
 static const char *pgstat_get_wait_ipc(WaitEventIPC w);
 static const char *pgstat_get_wait_timeout(WaitEventTimeout w);
 static const char *pgstat_get_wait_io(WaitEventIO w);
 
-static void pgstat_setheader(PgStat_MsgHdr *hdr, StatMsgType mtype);
-static void pgstat_send(void *msg, int len);
-
-static void pgstat_recv_inquiry(PgStat_MsgInquiry *msg, int len);
-static void pgstat_recv_tabstat(PgStat_MsgTabstat *msg, int len);
-static void pgstat_recv_tabpurge(PgStat_MsgTabpurge *msg, int len);
-static void pgstat_recv_dropdb(PgStat_MsgDropdb *msg, int len);
-static void pgstat_recv_resetcounter(PgStat_MsgResetcounter *msg, int len);
-static void pgstat_recv_resetsharedcounter(PgStat_MsgResetsharedcounter *msg, int len);
-static void pgstat_recv_resetsinglecounter(PgStat_MsgResetsinglecounter *msg, int len);
-static void pgstat_recv_autovac(PgStat_MsgAutovacStart *msg, int len);
-static void pgstat_recv_vacuum(PgStat_MsgVacuum *msg, int len);
-static void pgstat_recv_analyze(PgStat_MsgAnalyze *msg, int len);
-static void pgstat_recv_archiver(PgStat_MsgArchiver *msg, int len);
-static void pgstat_recv_bgwriter(PgStat_MsgBgWriter *msg, int len);
-static void pgstat_recv_funcstat(PgStat_MsgFuncstat *msg, int len);
-static void pgstat_recv_funcpurge(PgStat_MsgFuncpurge *msg, int len);
-static void pgstat_recv_recoveryconflict(PgStat_MsgRecoveryConflict *msg, int len);
-static void pgstat_recv_deadlock(PgStat_MsgDeadlock *msg, int len);
-static void pgstat_recv_checksum_failure(PgStat_MsgChecksumFailure *msg, int len);
-static void pgstat_recv_tempfile(PgStat_MsgTempFile *msg, int len);
-
 /* ------------------------------------------------------------
  * Public functions called from postmaster follow
  * ------------------------------------------------------------
  */
 
-/* ----------
- * pgstat_init() -
- *
- *	Called from postmaster at startup. Create the resources required
- *	by the statistics collector process.  If unable to do so, do not
- *	fail --- better to let the postmaster start with stats collection
- *	disabled.
- * ----------
+/*
+ * StatsShmemSize
+ *		Compute shared memory space needed for activity statistic
+ */
+Size
+StatsShmemSize(void)
+{
+	return sizeof(StatsShmemStruct);
+}
+
+/*
+ * StatsShmemInit - initialize during shared-memory creation
  */
 void
-pgstat_init(void)
+StatsShmemInit(void)
 {
-	ACCEPT_TYPE_ARG3 alen;
-	struct addrinfo *addrs = NULL,
-			   *addr,
-				hints;
-	int			ret;
-	fd_set		rset;
-	struct timeval tv;
-	char		test_byte;
-	int			sel_res;
-	int			tries = 0;
+	bool		found;
 
-#define TESTBYTEVAL ((char) 199)
+	StatsShmem = (StatsShmemStruct *)
+		ShmemInitStruct("Stats area", StatsShmemSize(),
+						&found);
 
-	/*
-	 * This static assertion verifies that we didn't mess up the calculations
-	 * involved in selecting maximum payload sizes for our UDP messages.
-	 * Because the only consequence of overrunning PGSTAT_MAX_MSG_SIZE would
-	 * be silent performance loss from fragmentation, it seems worth having a
-	 * compile-time cross-check that we didn't.
-	 */
-	StaticAssertStmt(sizeof(PgStat_Msg) <= PGSTAT_MAX_MSG_SIZE,
-					 "maximum stats message size exceeds PGSTAT_MAX_MSG_SIZE");
-
-	/*
-	 * Create the UDP socket for sending and receiving statistic messages
-	 */
-	hints.ai_flags = AI_PASSIVE;
-	hints.ai_family = AF_UNSPEC;
-	hints.ai_socktype = SOCK_DGRAM;
-	hints.ai_protocol = 0;
-	hints.ai_addrlen = 0;
-	hints.ai_addr = NULL;
-	hints.ai_canonname = NULL;
-	hints.ai_next = NULL;
-	ret = pg_getaddrinfo_all("localhost", NULL, &hints, &addrs);
-	if (ret || !addrs)
+	if (!IsUnderPostmaster)
 	{
-		ereport(LOG,
-				(errmsg("could not resolve \"localhost\": %s",
-						gai_strerror(ret))));
-		goto startup_failed;
+		Assert(!found);
+
+		StatsShmem->stats_dsa_handle = DSM_HANDLE_INVALID;
 	}
+}
 
-	/*
-	 * On some platforms, pg_getaddrinfo_all() may return multiple addresses
-	 * only one of which will actually work (eg, both IPv6 and IPv4 addresses
-	 * when kernel will reject IPv6).  Worse, the failure may occur at the
-	 * bind() or perhaps even connect() stage.  So we must loop through the
-	 * results till we find a working combination. We will generate LOG
-	 * messages, but no error, for bogus combinations.
-	 */
-	for (addr = addrs; addr; addr = addr->ai_next)
-	{
-#ifdef HAVE_UNIX_SOCKETS
-		/* Ignore AF_UNIX sockets, if any are returned. */
-		if (addr->ai_family == AF_UNIX)
-			continue;
-#endif
+/* ----------
+ * pgstat_setup_memcxt() -
+ *
+ *	Create pgStatLocalContext and pgStatSnapshotContext, if not already done.
+ * ----------
+ */
+static void
+pgstat_setup_memcxt(void)
+{
+	if (!pgStatLocalContext)
+		pgStatLocalContext =
+			AllocSetContextCreate(TopMemoryContext,
+								  "Backend statistics snapshot",
+								  ALLOCSET_SMALL_SIZES);
+
+	if (!pgStatSnapshotContext)
+		pgStatSnapshotContext =
+			AllocSetContextCreate(TopMemoryContext,
+								  "Database statistics snapshot",
+								  ALLOCSET_SMALL_SIZES);
+}
 
-		if (++tries > 1)
-			ereport(LOG,
-					(errmsg("trying another address for the statistics collector")));
 
-		/*
-		 * Create the socket.
-		 */
-		if ((pgStatSock = socket(addr->ai_family, SOCK_DGRAM, 0)) == PGINVALID_SOCKET)
-		{
-			ereport(LOG,
-					(errcode_for_socket_access(),
-					 errmsg("could not create socket for statistics collector: %m")));
-			continue;
-		}
+/* ----------
+ * attach_shared_stats() -
+ *
+ *	Attach shared or create stats memory. If we are the first process to use
+ *	activity stats system, read saved statistics files if any.
+ * ---------
+ */
+static void
+attach_shared_stats(void)
+{
+	MemoryContext oldcontext;
 
-		/*
-		 * Bind it to a kernel assigned port on localhost and get the assigned
-		 * port via getsockname().
-		 */
-		if (bind(pgStatSock, addr->ai_addr, addr->ai_addrlen) < 0)
-		{
-			ereport(LOG,
-					(errcode_for_socket_access(),
-					 errmsg("could not bind socket for statistics collector: %m")));
-			closesocket(pgStatSock);
-			pgStatSock = PGINVALID_SOCKET;
-			continue;
-		}
+	/*
+	 * Don't use dsm under postmaster, or when not tracking counts.
+	 */
+	if (!pgstat_track_counts || !IsUnderPostmaster)
+		return;
 
-		alen = sizeof(pgStatAddr);
-		if (getsockname(pgStatSock, (struct sockaddr *) &pgStatAddr, &alen) < 0)
-		{
-			ereport(LOG,
-					(errcode_for_socket_access(),
-					 errmsg("could not get address of socket for statistics collector: %m")));
-			closesocket(pgStatSock);
-			pgStatSock = PGINVALID_SOCKET;
-			continue;
-		}
+	pgstat_setup_memcxt();
 
-		/*
-		 * Connect the socket to its own address.  This saves a few cycles by
-		 * not having to respecify the target address on every send. This also
-		 * provides a kernel-level check that only packets from this same
-		 * address will be received.
-		 */
-		if (connect(pgStatSock, (struct sockaddr *) &pgStatAddr, alen) < 0)
-		{
-			ereport(LOG,
-					(errcode_for_socket_access(),
-					 errmsg("could not connect socket for statistics collector: %m")));
-			closesocket(pgStatSock);
-			pgStatSock = PGINVALID_SOCKET;
-			continue;
-		}
+	if (area)
+		return;
 
-		/*
-		 * Try to send and receive a one-byte test message on the socket. This
-		 * is to catch situations where the socket can be created but will not
-		 * actually pass data (for instance, because kernel packet filtering
-		 * rules prevent it).
-		 */
-		test_byte = TESTBYTEVAL;
+	oldcontext = MemoryContextSwitchTo(TopMemoryContext);
 
-retry1:
-		if (send(pgStatSock, &test_byte, 1, 0) != 1)
-		{
-			if (errno == EINTR)
-				goto retry1;	/* if interrupted, just retry */
-			ereport(LOG,
-					(errcode_for_socket_access(),
-					 errmsg("could not send test message on socket for statistics collector: %m")));
-			closesocket(pgStatSock);
-			pgStatSock = PGINVALID_SOCKET;
-			continue;
-		}
+	LWLockAcquire(StatsLock, LW_EXCLUSIVE);
 
-		/*
-		 * There could possibly be a little delay before the message can be
-		 * received.  We arbitrarily allow up to half a second before deciding
-		 * it's broken.
-		 */
-		for (;;)				/* need a loop to handle EINTR */
-		{
-			FD_ZERO(&rset);
-			FD_SET(pgStatSock, &rset);
+	/*
+	 * The last process is responsible to write out stats files at exit.
+	 * Maintain refcount so that processes going to exit can find whether it
+	 * is the last or not.
+	 */
+	if (StatsShmem->refcount > 0)
+		StatsShmem->refcount++;
+	else
+	{
+		/* We're the first process to attach the shared stats memory */
+		Assert(StatsShmem->stats_dsa_handle == DSM_HANDLE_INVALID);
 
-			tv.tv_sec = 0;
-			tv.tv_usec = 500000;
-			sel_res = select(pgStatSock + 1, &rset, NULL, NULL, &tv);
-			if (sel_res >= 0 || errno != EINTR)
-				break;
-		}
-		if (sel_res < 0)
-		{
-			ereport(LOG,
-					(errcode_for_socket_access(),
-					 errmsg("select() failed in statistics collector: %m")));
-			closesocket(pgStatSock);
-			pgStatSock = PGINVALID_SOCKET;
-			continue;
-		}
-		if (sel_res == 0 || !FD_ISSET(pgStatSock, &rset))
-		{
-			/*
-			 * This is the case we actually think is likely, so take pains to
-			 * give a specific message for it.
-			 *
-			 * errno will not be set meaningfully here, so don't use it.
-			 */
-			ereport(LOG,
-					(errcode(ERRCODE_CONNECTION_FAILURE),
-					 errmsg("test message did not get through on socket for statistics collector")));
-			closesocket(pgStatSock);
-			pgStatSock = PGINVALID_SOCKET;
-			continue;
-		}
+		/* Initialize shared memory area */
+		area = dsa_create(LWTRANCHE_STATS);
+		pgStatSharedHash = dshash_create(area, &dsh_rootparams, 0);
 
-		test_byte++;			/* just make sure variable is changed */
+		StatsShmem->stats_dsa_handle = dsa_get_handle(area);
+		StatsShmem->global_stats =
+			dsa_allocate0(area, sizeof(PgStat_GlobalStats));
+		StatsShmem->archiver_stats =
+			dsa_allocate0(area, sizeof(PgStat_ArchiverStats));
+		StatsShmem->hash_handle = dshash_get_hash_table_handle(pgStatSharedHash);
 
-retry2:
-		if (recv(pgStatSock, &test_byte, 1, 0) != 1)
-		{
-			if (errno == EINTR)
-				goto retry2;	/* if interrupted, just retry */
-			ereport(LOG,
-					(errcode_for_socket_access(),
-					 errmsg("could not receive test message on socket for statistics collector: %m")));
-			closesocket(pgStatSock);
-			pgStatSock = PGINVALID_SOCKET;
-			continue;
-		}
+		shared_globalStats = (PgStat_GlobalStats *)
+			dsa_get_address(area, StatsShmem->global_stats);
+		shared_archiverStats = (PgStat_ArchiverStats *)
+			dsa_get_address(area, StatsShmem->archiver_stats);
 
-		if (test_byte != TESTBYTEVAL)	/* strictly paranoia ... */
-		{
-			ereport(LOG,
-					(errcode(ERRCODE_INTERNAL_ERROR),
-					 errmsg("incorrect test message transmission on socket for statistics collector")));
-			closesocket(pgStatSock);
-			pgStatSock = PGINVALID_SOCKET;
-			continue;
-		}
+		/* Load saved data if any. */
+		pgstat_read_statsfiles();
 
-		/* If we get here, we have a working socket */
-		break;
+		StatsShmem->refcount = 1;
 	}
 
-	/* Did we find a working address? */
-	if (!addr || pgStatSock == PGINVALID_SOCKET)
-		goto startup_failed;
+	LWLockRelease(StatsLock);
 
 	/*
-	 * Set the socket to non-blocking IO.  This ensures that if the collector
-	 * falls behind, statistics messages will be discarded; backends won't
-	 * block waiting to send messages to the collector.
+	 * If we're not the first process, attach existing shared stats area
+	 * outside the StatsLock section.
 	 */
-	if (!pg_set_noblock(pgStatSock))
+	if (!area)
 	{
-		ereport(LOG,
-				(errcode_for_socket_access(),
-				 errmsg("could not set statistics collector socket to nonblocking mode: %m")));
-		goto startup_failed;
+		/* Attach shared area. */
+		area = dsa_attach(StatsShmem->stats_dsa_handle);
+		pgStatSharedHash = dshash_attach(area, &dsh_rootparams,
+										 StatsShmem->hash_handle, 0);
+
+		/* Setup local variables */
+		pgStatLocalHash = NULL;
+		shared_globalStats = (PgStat_GlobalStats *)
+			dsa_get_address(area, StatsShmem->global_stats);
+		shared_archiverStats = (PgStat_ArchiverStats *)
+			dsa_get_address(area, StatsShmem->archiver_stats);
 	}
 
-	/*
-	 * Try to ensure that the socket's receive buffer is at least
-	 * PGSTAT_MIN_RCVBUF bytes, so that it won't easily overflow and lose
-	 * data.  Use of UDP protocol means that we are willing to lose data under
-	 * heavy load, but we don't want it to happen just because of ridiculously
-	 * small default buffer sizes (such as 8KB on older Windows versions).
-	 */
-	{
-		int			old_rcvbuf;
-		int			new_rcvbuf;
-		ACCEPT_TYPE_ARG3 rcvbufsize = sizeof(old_rcvbuf);
-
-		if (getsockopt(pgStatSock, SOL_SOCKET, SO_RCVBUF,
-					   (char *) &old_rcvbuf, &rcvbufsize) < 0)
-		{
-			elog(LOG, "getsockopt(SO_RCVBUF) failed: %m");
-			/* if we can't get existing size, always try to set it */
-			old_rcvbuf = 0;
-		}
-
-		new_rcvbuf = PGSTAT_MIN_RCVBUF;
-		if (old_rcvbuf < new_rcvbuf)
-		{
-			if (setsockopt(pgStatSock, SOL_SOCKET, SO_RCVBUF,
-						   (char *) &new_rcvbuf, sizeof(new_rcvbuf)) < 0)
-				elog(LOG, "setsockopt(SO_RCVBUF) failed: %m");
-		}
-	}
-
-	pg_freeaddrinfo_all(hints.ai_family, addrs);
-
-	/* Now that we have a long-lived socket, tell fd.c about it. */
-	ReserveExternalFD();
+	MemoryContextSwitchTo(oldcontext);
 
-	return;
-
-startup_failed:
-	ereport(LOG,
-			(errmsg("disabling statistics collector for lack of working socket")));
-
-	if (addrs)
-		pg_freeaddrinfo_all(hints.ai_family, addrs);
-
-	if (pgStatSock != PGINVALID_SOCKET)
-		closesocket(pgStatSock);
-	pgStatSock = PGINVALID_SOCKET;
-
-	/*
-	 * Adjust GUC variables to suppress useless activity, and for debugging
-	 * purposes (seeing track_counts off is a clue that we failed here). We
-	 * use PGC_S_OVERRIDE because there is no point in trying to turn it back
-	 * on from postgresql.conf without a restart.
-	 */
-	SetConfigOption("track_counts", "off", PGC_INTERNAL, PGC_S_OVERRIDE);
+	/* don't detach automatically */
+	dsa_pin_mapping(area);
+	global_snapshot_is_valid = false;
 }
 
-/*
- * subroutine for pgstat_reset_all
+/* ----------
+ * detach_shared_stats() -
+ *
+ *	Detach shared stats. Write out to file if we're the last process and told
+ *	to do so.
+ * ----------
  */
 static void
-pgstat_reset_remove_files(const char *directory)
+detach_shared_stats(bool write_stats)
 {
-	DIR		   *dir;
-	struct dirent *entry;
-	char		fname[MAXPGPATH * 2];
+	/* immediately return if useless */
+	if (!area || !IsUnderPostmaster)
+		return;
 
-	dir = AllocateDir(directory);
-	while ((entry = ReadDir(dir, directory)) != NULL)
-	{
-		int			nchars;
-		Oid			tmp_oid;
+	LWLockAcquire(StatsLock, LW_EXCLUSIVE);
 
+	if (--StatsShmem->refcount < 1)
+	{
 		/*
-		 * Skip directory entries that don't match the file names we write.
-		 * See get_dbstat_filename for the database-specific pattern.
+		 * The process is the last one that is attaching the shared stats
+		 * memory. Write out the stats files if requested.
 		 */
-		if (strncmp(entry->d_name, "global.", 7) == 0)
-			nchars = 7;
-		else
-		{
-			nchars = 0;
-			(void) sscanf(entry->d_name, "db_%u.%n",
-						  &tmp_oid, &nchars);
-			if (nchars <= 0)
-				continue;
-			/* %u allows leading whitespace, so reject that */
-			if (strchr("0123456789", entry->d_name[3]) == NULL)
-				continue;
-		}
-
-		if (strcmp(entry->d_name + nchars, "tmp") != 0 &&
-			strcmp(entry->d_name + nchars, "stat") != 0)
-			continue;
+		if (write_stats)
+			pgstat_write_statsfiles();
 
-		snprintf(fname, sizeof(fname), "%s/%s", directory,
-				 entry->d_name);
-		unlink(fname);
+		/* No one is using the area. */
+		StatsShmem->stats_dsa_handle = DSM_HANDLE_INVALID;
 	}
-	FreeDir(dir);
+
+	LWLockRelease(StatsLock);
+
+	/*
+	 * Detach the area. Automatically destroyed when the last process detached
+	 * it.
+	 */
+	dsa_detach(area);
+
+	area = NULL;
+	pgStatSharedHash = NULL;
+	shared_globalStats = NULL;
+	shared_archiverStats = NULL;
+	pgStatLocalHash = NULL;
+	global_snapshot_is_valid = false;
 }
 
 /*
  * pgstat_reset_all() -
  *
- * Remove the stats files.  This is currently used only if WAL
- * recovery is needed after a crash.
+ * Remove the stats file.  This is currently used only if WAL recovery is
+ * needed after a crash.
  */
 void
 pgstat_reset_all(void)
 {
-	pgstat_reset_remove_files(pgstat_stat_directory);
-	pgstat_reset_remove_files(PGSTAT_STAT_PERMANENT_DIRECTORY);
-}
+	/* standalone server doesn't use shared stats */
+	if (!IsUnderPostmaster)
+		return;
 
-#ifdef EXEC_BACKEND
+	/* we must have shared stats attached */
+	Assert(StatsShmem->stats_dsa_handle != DSM_HANDLE_INVALID);
 
-/*
- * pgstat_forkexec() -
- *
- * Format up the arglist for, then fork and exec, statistics collector process
- */
-static pid_t
-pgstat_forkexec(void)
-{
-	char	   *av[10];
-	int			ac = 0;
-
-	av[ac++] = "postgres";
-	av[ac++] = "--forkcol";
-	av[ac++] = NULL;			/* filled in by postmaster_forkexec */
-
-	av[ac] = NULL;
-	Assert(ac < lengthof(av));
-
-	return postmaster_forkexec(ac, av);
-}
-#endif							/* EXEC_BACKEND */
-
-
-/*
- * pgstat_start() -
- *
- *	Called from postmaster at startup or after an existing collector
- *	died.  Attempt to fire up a fresh statistics collector.
- *
- *	Returns PID of child process, or 0 if fail.
- *
- *	Note: if fail, we will be called again from the postmaster main loop.
- */
-int
-pgstat_start(void)
-{
-	time_t		curtime;
-	pid_t		pgStatPid;
-
-	/*
-	 * Check that the socket is there, else pgstat_init failed and we can do
-	 * nothing useful.
-	 */
-	if (pgStatSock == PGINVALID_SOCKET)
-		return 0;
-
-	/*
-	 * Do nothing if too soon since last collector start.  This is a safety
-	 * valve to protect against continuous respawn attempts if the collector
-	 * is dying immediately at launch.  Note that since we will be re-called
-	 * from the postmaster main loop, we will get another chance later.
-	 */
-	curtime = time(NULL);
-	if ((unsigned int) (curtime - last_pgstat_start_time) <
-		(unsigned int) PGSTAT_RESTART_INTERVAL)
-		return 0;
-	last_pgstat_start_time = curtime;
+	/* Startup must be the only user of shared stats */
+	Assert(StatsShmem->refcount == 1);
 
 	/*
-	 * Okay, fork off the collector.
+	 * We could directly remove files and recreate the shared memory area. But
+	 * just discard  then create for simplicity.
 	 */
-#ifdef EXEC_BACKEND
-	switch ((pgStatPid = pgstat_forkexec()))
-#else
-	switch ((pgStatPid = fork_process()))
-#endif
-	{
-		case -1:
-			ereport(LOG,
-					(errmsg("could not fork statistics collector: %m")));
-			return 0;
-
-#ifndef EXEC_BACKEND
-		case 0:
-			/* in postmaster child ... */
-			InitPostmasterChild();
-
-			/* Close the postmaster's sockets */
-			ClosePostmasterPorts(false);
-
-			/* Drop our connection to postmaster's shared memory, as well */
-			dsm_detach_all();
-			PGSharedMemoryDetach();
-
-			PgstatCollectorMain(0, NULL);
-			break;
-#endif
-
-		default:
-			return (int) pgStatPid;
-	}
-
-	/* shouldn't get here */
-	return 0;
-}
-
-void
-allow_immediate_pgstat_restart(void)
-{
-	last_pgstat_start_time = 0;
+	detach_shared_stats(false); /* Don't write files. */
+	attach_shared_stats();
 }
 
 /* ------------------------------------------------------------
@@ -794,144 +593,488 @@ allow_immediate_pgstat_restart(void)
  *------------------------------------------------------------
  */
 
-
 /* ----------
  * pgstat_report_stat() -
  *
  *	Must be called by processes that performs DML: tcop/postgres.c, logical
- *	receiver processes, SPI worker, etc. to send the so far collected
- *	per-table and function usage statistics to the collector.  Note that this
- *	is called only when not within a transaction, so it is fair to use
+ *	receiver processes, SPI worker, etc. to apply the so far collected
+ *	per-table and function usage statistics to the shared statistics hashes.
+ *
+ *	Updates are applied not more frequent than the interval of
+ *	PGSTAT_MIN_INTERVAL milliseconds. They are also postponed on lock
+ *	failure if force is false and there's no pending updates longer than
+ *	PGSTAT_MAX_INTERVAL milliseconds. Postponed updates are retried in
+ *	succeeding calls of this function.
+ *
+ *	Returns the time until the next timing when updates are applied in
+ *	milliseconds if there are no updates held for more than
+ *	PGSTAT_MIN_INTERVAL milliseconds.
+ *
+ *	Note that this is called only out of a transaction, so it is fine to use
  *	transaction stop time as an approximation of current time.
- * ----------
+ *	----------
  */
-void
+long
 pgstat_report_stat(bool force)
 {
-	/* we assume this inits to all zeroes: */
-	static const PgStat_TableCounts all_zeroes;
-	static TimestampTz last_report = 0;
-
+	static TimestampTz next_flush = 0;
+	static TimestampTz pending_since = 0;
+	static long retry_interval = 0;
 	TimestampTz now;
-	PgStat_MsgTabstat regular_msg;
-	PgStat_MsgTabstat shared_msg;
-	TabStatusArray *tsa;
+	bool		nowait = !force;	/* Don't use force ever after */
+	HASH_SEQ_STATUS scan;
+	PgStatLocalHashEntry *lent;
+	PgStatLocalHashEntry **dbentlist;
+	int			dbentlistlen = 8;
+	int			ndbentries = 0;
+	int			remains = 0;
 	int			i;
 
 	/* Don't expend a clock check if nothing to do */
-	if ((pgStatTabList == NULL || pgStatTabList->tsa_used == 0) &&
-		pgStatXactCommit == 0 && pgStatXactRollback == 0 &&
-		!have_function_stats)
-		return;
+	if (area == NULL || !HAVE_ANY_PENDING_STATS())
+		return 0;
+
+	dbentlist = palloc(sizeof(PgStatLocalHashEntry *) * dbentlistlen);
 
-	/*
-	 * Don't send a message unless it's been at least PGSTAT_STAT_INTERVAL
-	 * msec since we last sent one, or the caller wants to force stats out.
-	 */
 	now = GetCurrentTransactionStopTimestamp();
-	if (!force &&
-		!TimestampDifferenceExceeds(last_report, now, PGSTAT_STAT_INTERVAL))
-		return;
-	last_report = now;
 
-	/*
-	 * Destroy pgStatTabHash before we start invalidating PgStat_TableEntry
-	 * entries it points to.  (Should we fail partway through the loop below,
-	 * it's okay to have removed the hashtable already --- the only
-	 * consequence is we'd get multiple entries for the same table in the
-	 * pgStatTabList, and that's safe.)
-	 */
-	if (pgStatTabHash)
-		hash_destroy(pgStatTabHash);
-	pgStatTabHash = NULL;
+	if (nowait)
+	{
+		/*
+		 * Don't flush stats too frequently.  Return the time to the next
+		 * flush.
+		 */
+		if (now < next_flush)
+		{
+			/* Record the epoch time if retrying. */
+			if (pending_since == 0)
+				pending_since = now;
+
+			return (next_flush - now) / 1000;
+		}
+
+		/* But, don't keep pending updates longer than PGSTAT_MAX_INTERVAL. */
+
+		if (pending_since > 0 &&
+			TimestampDifferenceExceeds(pending_since, now, PGSTAT_MAX_INTERVAL))
+			nowait = false;
+	}
 
 	/*
-	 * Scan through the TabStatusArray struct(s) to find tables that actually
-	 * have counts, and build messages to send.  We have to separate shared
-	 * relations from regular ones because the databaseid field in the message
-	 * header has to depend on that.
+	 * flush_tabstat applies some of stats numbers of flushed entries into
+	 * local database stats. So flush-out database stats later.
 	 */
-	regular_msg.m_databaseid = MyDatabaseId;
-	shared_msg.m_databaseid = InvalidOid;
-	regular_msg.m_nentries = 0;
-	shared_msg.m_nentries = 0;
-
-	for (tsa = pgStatTabList; tsa != NULL; tsa = tsa->tsa_next)
+	if (pgStatLocalHash)
 	{
-		for (i = 0; i < tsa->tsa_used; i++)
+		/* Step 1: flush out other than database stats */
+		hash_seq_init(&scan, pgStatLocalHash);
+		while ((lent = (PgStatLocalHashEntry *) hash_seq_search(&scan)) != NULL)
 		{
-			PgStat_TableStatus *entry = &tsa->tsa_entries[i];
-			PgStat_MsgTabstat *this_msg;
-			PgStat_TableEntry *this_ent;
+			bool		remove = false;
 
-			/* Shouldn't have any pending transaction-dependent counts */
-			Assert(entry->trans == NULL);
+			switch (lent->env->type)
+			{
+				case PGSTAT_TYPE_DB:
+					if (ndbentries >= dbentlistlen)
+					{
+						dbentlistlen *= 2;
+						dbentlist = repalloc(dbentlist,
+											 sizeof(PgStatLocalHashEntry *) *
+											 dbentlistlen);
+					}
+					dbentlist[ndbentries++] = lent;
+					break;
+				case PGSTAT_TYPE_TABLE:
+					if (flush_tabstat(lent->env, nowait))
+						remove = true;
+					break;
+				case PGSTAT_TYPE_FUNCTION:
+					if (flush_funcstat(lent->env, nowait))
+						remove = true;
+					break;
+				default:
+					Assert(false);
+			}
 
-			/*
-			 * Ignore entries that didn't accumulate any actual counts, such
-			 * as indexes that were opened by the planner but not used.
-			 */
-			if (memcmp(&entry->t_counts, &all_zeroes,
-					   sizeof(PgStat_TableCounts)) == 0)
+			if (!remove)
+			{
+				remains++;
 				continue;
+			}
 
-			/*
-			 * OK, insert data into the appropriate message, and send if full.
-			 */
-			this_msg = entry->t_shared ? &shared_msg : &regular_msg;
-			this_ent = &this_msg->m_entry[this_msg->m_nentries];
-			this_ent->t_id = entry->t_id;
-			memcpy(&this_ent->t_counts, &entry->t_counts,
-				   sizeof(PgStat_TableCounts));
-			if (++this_msg->m_nentries >= PGSTAT_NUM_TABENTRIES)
+			/* Remove the successfully flushed entry */
+			pfree(lent->env);
+			hash_search(pgStatLocalHash, &lent->key, HASH_REMOVE, NULL);
+		}
+
+		/* Step 2: flush out database stats */
+		for (i = 0; i < ndbentries; i++)
+		{
+			PgStatLocalHashEntry *lent = dbentlist[i];
+
+			if (flush_dbstat(lent->env, nowait))
 			{
-				pgstat_send_tabstat(this_msg);
-				this_msg->m_nentries = 0;
+				remains--;
+				/* Remove the successfully flushed entry */
+				pfree(lent->env);
+				hash_search(pgStatLocalHash, &lent->key, HASH_REMOVE, NULL);
 			}
 		}
-		/* zero out PgStat_TableStatus structs after use */
-		MemSet(tsa->tsa_entries, 0,
-			   tsa->tsa_used * sizeof(PgStat_TableStatus));
-		tsa->tsa_used = 0;
+		pfree(dbentlist);
+
+		if (remains <= 0)
+		{
+			hash_destroy(pgStatLocalHash);
+			pgStatLocalHash = NULL;
+		}
+	}
+
+	/* Publish the last flush time */
+	LWLockAcquire(StatsLock, LW_EXCLUSIVE);
+	if (shared_globalStats->stats_timestamp < now)
+		shared_globalStats->stats_timestamp = now;
+	LWLockRelease(StatsLock);
+
+	/*
+	 * If we have pending local stats, let the caller know the retry interval.
+	 */
+	if (HAVE_ANY_PENDING_STATS())
+	{
+		/* Retain the epoch time */
+		if (pending_since == 0)
+			pending_since = now;
+
+		/* The interval is doubled at every retry. */
+		if (retry_interval == 0)
+			retry_interval = PGSTAT_RETRY_MIN_INTERVAL * 1000;
+		else
+			retry_interval = retry_interval * 2;
+
+		/*
+		 * Determine the next retry interval so as not to get shorter than the
+		 * previous interval.
+		 */
+		if (!TimestampDifferenceExceeds(pending_since,
+										now + 2 * retry_interval,
+										PGSTAT_MAX_INTERVAL))
+			next_flush = now + retry_interval;
+		else
+		{
+			next_flush = pending_since + PGSTAT_MAX_INTERVAL * 1000;
+			retry_interval = next_flush - now;
+		}
+
+		return retry_interval / 1000;
 	}
 
+	/* Set the next time to update stats */
+	next_flush = now + PGSTAT_MIN_INTERVAL * 1000;
+	retry_interval = 0;
+	pending_since = 0;
+
+	return 0;
+}
+
+/*
+ * flush_tabstat - flush out a local table stats entry
+ *
+ * Some of the stats numbers are copied to local database stats entry after
+ * successful flush-out.
+ *
+ * If nowait is true, this function returns false on lock failure. Otherwise
+ * this function always returns true.
+ *
+ * Returns true if the entry is successfully flushed out.
+ */
+static bool
+flush_tabstat(PgStatEnvelope * lenv, bool nowait)
+{
+	static const PgStat_TableCounts all_zeroes;
+	Oid			dboid;			/* database OID of the table */
+	PgStat_TableStatus *lstats; /* local stats entry  */
+	PgStatEnvelope *shenv;		/* shared stats envelope */
+	PgStat_StatTabEntry *shtabstats;	/* table entry of shared stats */
+	PgStat_StatDBEntry *ldbstats;	/* local database entry */
+	bool		found;
+
+	Assert(lenv->type == PGSTAT_TYPE_TABLE);
+
+	lstats = (PgStat_TableStatus *) &lenv->body;
+	dboid = lstats->t_shared ? InvalidOid : MyDatabaseId;
+
+	/*
+	 * Ignore entries that didn't accumulate any actual counts, such as
+	 * indexes that were opened by the planner but not used.
+	 */
+	if (memcmp(&lstats->t_counts, &all_zeroes,
+			   sizeof(PgStat_TableCounts)) == 0)
+		return true;
+
+	/* find shared table stats entry corresponding to the local entry */
+	shenv = get_stat_entry(PGSTAT_TYPE_TABLE, dboid, lstats->t_id,
+						   nowait, init_tabentry, &found);
+
+	/* skip if dshash failed to acquire lock */
+	if (shenv == NULL)
+		return false;
+
+	/* retrieve the shared table stats entry from the envelope */
+	shtabstats = (PgStat_StatTabEntry *) &shenv->body;
+
+	/* lock the shared entry to protect the content, skip if failed */
+	if (!nowait)
+		LWLockAcquire(&shenv->lock, LW_EXCLUSIVE);
+	else if (!LWLockConditionalAcquire(&shenv->lock, LW_EXCLUSIVE))
+		return false;
+
+	/* add the values to the shared entry. */
+	shtabstats->numscans += lstats->t_counts.t_numscans;
+	shtabstats->tuples_returned += lstats->t_counts.t_tuples_returned;
+	shtabstats->tuples_fetched += lstats->t_counts.t_tuples_fetched;
+	shtabstats->tuples_inserted += lstats->t_counts.t_tuples_inserted;
+	shtabstats->tuples_updated += lstats->t_counts.t_tuples_updated;
+	shtabstats->tuples_deleted += lstats->t_counts.t_tuples_deleted;
+	shtabstats->tuples_hot_updated += lstats->t_counts.t_tuples_hot_updated;
+
+	/*
+	 * If table was truncated or vacuum/analyze has ran, first reset the
+	 * live/dead counters.
+	 */
+	if (lstats->t_counts.t_truncated ||
+		lstats->t_counts.vacuum_count > 0 ||
+		lstats->t_counts.analyze_count > 0 ||
+		lstats->t_counts.autovac_vacuum_count > 0 ||
+		lstats->t_counts.autovac_analyze_count > 0)
+	{
+		shtabstats->n_live_tuples = 0;
+		shtabstats->n_dead_tuples = 0;
+	}
+
+	/* clear the change counter if requested */
+	if (lstats->t_counts.reset_changed_tuples)
+		shtabstats->changes_since_analyze = 0;
+
+	shtabstats->n_live_tuples += lstats->t_counts.t_delta_live_tuples;
+	shtabstats->n_dead_tuples += lstats->t_counts.t_delta_dead_tuples;
+	shtabstats->changes_since_analyze += lstats->t_counts.t_changed_tuples;
+	shtabstats->blocks_fetched += lstats->t_counts.t_blocks_fetched;
+	shtabstats->blocks_hit += lstats->t_counts.t_blocks_hit;
+
+	/*
+	 * Update vacuum/analyze timestamp and counters, so that the values won't
+	 * goes back.
+	 */
+	if (shtabstats->vacuum_timestamp < lstats->vacuum_timestamp)
+		shtabstats->vacuum_timestamp = lstats->vacuum_timestamp;
+	shtabstats->vacuum_count += lstats->t_counts.vacuum_count;
+
+	if (shtabstats->autovac_vacuum_timestamp < lstats->autovac_vacuum_timestamp)
+		shtabstats->autovac_vacuum_timestamp = lstats->autovac_vacuum_timestamp;
+	shtabstats->autovac_vacuum_count += lstats->t_counts.autovac_vacuum_count;
+
+	if (shtabstats->analyze_timestamp < lstats->analyze_timestamp)
+		shtabstats->analyze_timestamp = lstats->analyze_timestamp;
+	shtabstats->analyze_count += lstats->t_counts.analyze_count;
+
+	if (shtabstats->autovac_analyze_timestamp < lstats->autovac_analyze_timestamp)
+		shtabstats->autovac_analyze_timestamp = lstats->autovac_analyze_timestamp;
+	shtabstats->autovac_analyze_count += lstats->t_counts.autovac_analyze_count;
+
+	/* Clamp n_live_tuples in case of negative delta_live_tuples */
+	shtabstats->n_live_tuples = Max(shtabstats->n_live_tuples, 0);
+	/* Likewise for n_dead_tuples */
+	shtabstats->n_dead_tuples = Max(shtabstats->n_dead_tuples, 0);
+
+	LWLockRelease(&shenv->lock);
+
+	/* The entry is successfully flushed so the same to add to database stats */
+	ldbstats = get_local_dbstat_entry(dboid);
+	ldbstats->counts.n_tuples_returned += lstats->t_counts.t_tuples_returned;
+	ldbstats->counts.n_tuples_fetched += lstats->t_counts.t_tuples_fetched;
+	ldbstats->counts.n_tuples_inserted += lstats->t_counts.t_tuples_inserted;
+	ldbstats->counts.n_tuples_updated += lstats->t_counts.t_tuples_updated;
+	ldbstats->counts.n_tuples_deleted += lstats->t_counts.t_tuples_deleted;
+	ldbstats->counts.n_blocks_fetched += lstats->t_counts.t_blocks_fetched;
+	ldbstats->counts.n_blocks_hit += lstats->t_counts.t_blocks_hit;
+
+	return true;
+}
+
+/* ----------
+ * init_tabentry() -
+ *
+ * initializes table stats entry
+ * This is also used as initialization callback for get_stat_entry.
+ * ----------
+ */
+static void
+init_tabentry(PgStatEnvelope * env)
+{
+	PgStat_StatTabEntry *tabent = (PgStat_StatTabEntry *) &env->body;
+
 	/*
-	 * Send partial messages.  Make sure that any pending xact commit/abort
-	 * gets counted, even if there are no table stats to send.
+	 * If it's a new table entry, initialize counters to the values we just
+	 * got.
 	 */
-	if (regular_msg.m_nentries > 0 ||
-		pgStatXactCommit > 0 || pgStatXactRollback > 0)
-		pgstat_send_tabstat(&regular_msg);
-	if (shared_msg.m_nentries > 0)
-		pgstat_send_tabstat(&shared_msg);
-
-	/* Now, send function statistics */
-	pgstat_send_funcstats();
+	Assert(env->type == PGSTAT_TYPE_TABLE);
+	tabent->tableid = env->objectid;
+	tabent->numscans = 0;
+	tabent->tuples_returned = 0;
+	tabent->tuples_fetched = 0;
+	tabent->tuples_inserted = 0;
+	tabent->tuples_updated = 0;
+	tabent->tuples_deleted = 0;
+	tabent->tuples_hot_updated = 0;
+	tabent->n_live_tuples = 0;
+	tabent->n_dead_tuples = 0;
+	tabent->changes_since_analyze = 0;
+	tabent->blocks_fetched = 0;
+	tabent->blocks_hit = 0;
+
+	tabent->vacuum_timestamp = 0;
+	tabent->vacuum_count = 0;
+	tabent->autovac_vacuum_timestamp = 0;
+	tabent->autovac_vacuum_count = 0;
+	tabent->analyze_timestamp = 0;
+	tabent->analyze_count = 0;
+	tabent->autovac_analyze_timestamp = 0;
+	tabent->autovac_analyze_count = 0;
 }
 
+
 /*
- * Subroutine for pgstat_report_stat: finish and send a tabstat message
+ * flush_funcstat - flush out a local function stats entry
+ *
+ * If nowait is true, this function returns false on lock failure. Otherwise
+ * this function always returns true.
+ *
+ * Returns true if the entry is successfully flushed out.
+ */
+static bool
+flush_funcstat(PgStatEnvelope * env, bool nowait)
+{
+	/* we assume this inits to all zeroes: */
+	static const PgStat_FunctionCounts all_zeroes;
+	PgStat_BackendFunctionEntry *localent;	/* local stats entry */
+	PgStatEnvelope *shenv;		/* shared stats envelope */
+	PgStat_StatFuncEntry *sharedent = NULL; /* shared stats entry */
+	bool		found;
+
+	Assert(env->type == PGSTAT_TYPE_FUNCTION);
+	localent = (PgStat_BackendFunctionEntry *) &env->body;
+
+	/* Skip it if no counts accumulated for it so far */
+	if (memcmp(&localent->f_counts, &all_zeroes,
+			   sizeof(PgStat_FunctionCounts)) == 0)
+		return true;
+
+	/* find shared table stats entry corresponding to the local entry */
+	shenv = get_stat_entry(PGSTAT_TYPE_FUNCTION, MyDatabaseId, localent->f_id,
+						   nowait, init_funcentry, &found);
+	/* skip if dshash failed to acquire lock */
+	if (sharedent == NULL)
+		return false;			/* failed to acquire lock, skip */
+
+	/* retrieve the shared table stats entry from the envelope */
+	sharedent = (PgStat_StatFuncEntry *) &shenv->body;
+
+	/* lock the shared entry to protect the content, skip if failed */
+	if (!nowait)
+		LWLockAcquire(&shenv->lock, LW_EXCLUSIVE);
+	else if (!LWLockConditionalAcquire(&shenv->lock, LW_EXCLUSIVE))
+		return false;			/* failed to acquire lock, skip */
+
+	sharedent->f_numcalls += localent->f_counts.f_numcalls;
+	sharedent->f_total_time +=
+		INSTR_TIME_GET_MICROSEC(localent->f_counts.f_total_time);
+	sharedent->f_self_time +=
+		INSTR_TIME_GET_MICROSEC(localent->f_counts.f_self_time);
+
+	LWLockRelease(&shenv->lock);
+
+	return true;
+}
+
+
+/* ----------
+ * init_funcentry() -
+ *
+ * initializes function stats entry
+ * This is also used as initialization callback for get_stat_entry.
+ * ----------
  */
 static void
-pgstat_send_tabstat(PgStat_MsgTabstat *tsmsg)
+init_funcentry(PgStatEnvelope * env)
 {
-	int			n;
-	int			len;
+	PgStat_StatFuncEntry *shstat = (PgStat_StatFuncEntry *) &env->body;
+
+	Assert(env->type == PGSTAT_TYPE_FUNCTION);
+	shstat->functionid = env->objectid;
+	shstat->f_numcalls = 0;
+	shstat->f_total_time = 0;
+	shstat->f_self_time = 0;
+}
+
+
+/*
+ * flush_dbstat - flush out a local database stats entry
+ *
+ * If nowait is true, this function returns false on lock failure. Otherwise
+ * this function always returns true.
+ *
+ * Returns true if the entry is successfully flushed out.
+ */
+static bool
+flush_dbstat(PgStatEnvelope * env, bool nowait)
+{
+	PgStat_StatDBEntry *localent;
+	PgStatEnvelope *shenv;
+	PgStat_StatDBEntry *sharedent;
+
+	Assert(env->type == PGSTAT_TYPE_DB);
+
+	localent = (PgStat_StatDBEntry *) &env->body;
+
+	/* find shared database stats entry corresponding to the local entry */
+	shenv = get_stat_entry(PGSTAT_TYPE_DB, localent->databaseid, InvalidOid,
+						   nowait, init_dbentry, NULL);
+
+	/* skip if dshash failed to acquire lock */
+	if (!shenv)
+		return false;
+
+	/* retrieve the shared stats entry from the envelope */
+	sharedent = (PgStat_StatDBEntry *) &shenv->body;
+
+	/* lock the shared entry to protect the content, skip if failed */
+	if (!nowait)
+		LWLockAcquire(&shenv->lock, LW_EXCLUSIVE);
+	else if (!LWLockConditionalAcquire(&shenv->lock, LW_EXCLUSIVE))
+		return false;
+
+	sharedent->counts.n_tuples_returned += localent->counts.n_tuples_returned;
+	sharedent->counts.n_tuples_fetched += localent->counts.n_tuples_fetched;
+	sharedent->counts.n_tuples_inserted += localent->counts.n_tuples_inserted;
+	sharedent->counts.n_tuples_updated += localent->counts.n_tuples_updated;
+	sharedent->counts.n_tuples_deleted += localent->counts.n_tuples_deleted;
+	sharedent->counts.n_blocks_fetched += localent->counts.n_blocks_fetched;
+	sharedent->counts.n_blocks_hit += localent->counts.n_blocks_hit;
 
-	/* It's unlikely we'd get here with no socket, but maybe not impossible */
-	if (pgStatSock == PGINVALID_SOCKET)
-		return;
+	sharedent->counts.n_deadlocks += localent->counts.n_deadlocks;
+	sharedent->counts.n_temp_bytes += localent->counts.n_temp_bytes;
+	sharedent->counts.n_temp_files += localent->counts.n_temp_files;
+	sharedent->counts.n_checksum_failures += localent->counts.n_checksum_failures;
 
 	/*
-	 * Report and reset accumulated xact commit/rollback and I/O timings
-	 * whenever we send a normal tabstat message
+	 * Accumulate xact commit/rollback and I/O timings to stats entry of the
+	 * current database.
 	 */
-	if (OidIsValid(tsmsg->m_databaseid))
+	if (OidIsValid(localent->databaseid))
 	{
-		tsmsg->m_xact_commit = pgStatXactCommit;
-		tsmsg->m_xact_rollback = pgStatXactRollback;
-		tsmsg->m_block_read_time = pgStatBlockReadTime;
-		tsmsg->m_block_write_time = pgStatBlockWriteTime;
+		sharedent->counts.n_xact_commit += pgStatXactCommit;
+		sharedent->counts.n_xact_rollback += pgStatXactRollback;
+		sharedent->counts.n_block_read_time += pgStatBlockReadTime;
+		sharedent->counts.n_block_write_time += pgStatBlockWriteTime;
 		pgStatXactCommit = 0;
 		pgStatXactRollback = 0;
 		pgStatBlockReadTime = 0;
@@ -939,257 +1082,102 @@ pgstat_send_tabstat(PgStat_MsgTabstat *tsmsg)
 	}
 	else
 	{
-		tsmsg->m_xact_commit = 0;
-		tsmsg->m_xact_rollback = 0;
-		tsmsg->m_block_read_time = 0;
-		tsmsg->m_block_write_time = 0;
+		sharedent->counts.n_xact_commit = 0;
+		sharedent->counts.n_xact_rollback = 0;
+		sharedent->counts.n_block_read_time = 0;
+		sharedent->counts.n_block_write_time = 0;
 	}
 
-	n = tsmsg->m_nentries;
-	len = offsetof(PgStat_MsgTabstat, m_entry[0]) +
-		n * sizeof(PgStat_TableEntry);
+	LWLockRelease(&shenv->lock);
 
-	pgstat_setheader(&tsmsg->m_hdr, PGSTAT_MTYPE_TABSTAT);
-	pgstat_send(tsmsg, len);
+	return true;
 }
 
+
+/* ----------
+ * init_dbentry() -
+ *
+ * initializes database stats entry
+ * This is also used as initialization callback for get_stat_entry.
+ * ----------
+ */
+static void
+init_dbentry(PgStatEnvelope * env)
+{
+	PgStat_StatDBEntry *dbentry = (PgStat_StatDBEntry *) &env->body;
+
+	Assert(env->type == PGSTAT_TYPE_DB);
+	dbentry->databaseid = env->databaseid;
+	dbentry->last_autovac_time = 0;
+	dbentry->last_checksum_failure = 0;
+	dbentry->stat_reset_timestamp = 0;
+	dbentry->stats_timestamp = 0;
+	/* initialize the new shared entry */
+	MemSet(&dbentry->counts, 0, sizeof(PgStat_StatDBCounts));
+}
+
+
 /*
- * Subroutine for pgstat_report_stat: populate and send a function stat message
+ * Create the filename for a DB stat file; filename is output parameter points
+ * to a character buffer of length len.
  */
 static void
-pgstat_send_funcstats(void)
+get_dbstat_filename(bool tempname, Oid databaseid, char *filename, int len)
 {
-	/* we assume this inits to all zeroes: */
-	static const PgStat_FunctionCounts all_zeroes;
-
-	PgStat_MsgFuncstat msg;
-	PgStat_BackendFunctionEntry *entry;
-	HASH_SEQ_STATUS fstat;
-
-	if (pgStatFunctions == NULL)
-		return;
-
-	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_FUNCSTAT);
-	msg.m_databaseid = MyDatabaseId;
-	msg.m_nentries = 0;
-
-	hash_seq_init(&fstat, pgStatFunctions);
-	while ((entry = (PgStat_BackendFunctionEntry *) hash_seq_search(&fstat)) != NULL)
-	{
-		PgStat_FunctionEntry *m_ent;
-
-		/* Skip it if no counts accumulated since last time */
-		if (memcmp(&entry->f_counts, &all_zeroes,
-				   sizeof(PgStat_FunctionCounts)) == 0)
-			continue;
-
-		/* need to convert format of time accumulators */
-		m_ent = &msg.m_entry[msg.m_nentries];
-		m_ent->f_id = entry->f_id;
-		m_ent->f_numcalls = entry->f_counts.f_numcalls;
-		m_ent->f_total_time = INSTR_TIME_GET_MICROSEC(entry->f_counts.f_total_time);
-		m_ent->f_self_time = INSTR_TIME_GET_MICROSEC(entry->f_counts.f_self_time);
-
-		if (++msg.m_nentries >= PGSTAT_NUM_FUNCENTRIES)
-		{
-			pgstat_send(&msg, offsetof(PgStat_MsgFuncstat, m_entry[0]) +
-						msg.m_nentries * sizeof(PgStat_FunctionEntry));
-			msg.m_nentries = 0;
-		}
-
-		/* reset the entry's counts */
-		MemSet(&entry->f_counts, 0, sizeof(PgStat_FunctionCounts));
-	}
-
-	if (msg.m_nentries > 0)
-		pgstat_send(&msg, offsetof(PgStat_MsgFuncstat, m_entry[0]) +
-					msg.m_nentries * sizeof(PgStat_FunctionEntry));
-
-	have_function_stats = false;
+	int			printed;
+
+	/* NB -- pgstat_reset_remove_files knows about the pattern this uses */
+	printed = snprintf(filename, len, "%s/db_%u.%s",
+					   PGSTAT_STAT_PERMANENT_DIRECTORY,
+					   databaseid,
+					   tempname ? "tmp" : "stat");
+	if (printed >= len)
+		elog(ERROR, "overlength pgstat path");
 }

 /* ----------
- * pgstat_vacuum_stat() -
+ * collect_stat_entries() -
  *
- *	Will tell the collector about objects he can get rid of.
+ *	Collect the shared statistics entries specified by type and dbid. Returns a
+ *  list of pointer to shared statistics in palloc'ed memory. If type is
+ *  PGSTAT_TYPE_ALL, all types of statistics of the database is collected. If
+ *  type is PGSTAT_TYPE_DB, the parameter dbid is ignored and collect all
+ *  PGSTAT_TYPE_DB entries.
  * ----------
  */
-void
-pgstat_vacuum_stat(void)
+static PgStatEnvelope * *collect_stat_entries(PgStatTypes type, Oid dbid)
 {
-	HTAB	   *htab;
-	PgStat_MsgTabpurge msg;
-	PgStat_MsgFuncpurge f_msg;
-	HASH_SEQ_STATUS hstat;
-	PgStat_StatDBEntry *dbentry;
-	PgStat_StatTabEntry *tabentry;
-	PgStat_StatFuncEntry *funcentry;
-	int			len;
-
-	if (pgStatSock == PGINVALID_SOCKET)
-		return;
-
-	/*
-	 * If not done for this transaction, read the statistics collector stats
-	 * file into some hash tables.
-	 */
-	backend_read_statsfile();
-
-	/*
-	 * Read pg_database and make a list of OIDs of all existing databases
-	 */
-	htab = pgstat_collect_oids(DatabaseRelationId, Anum_pg_database_oid);
-
-	/*
-	 * Search the database hash table for dead databases and tell the
-	 * collector to drop them.
-	 */
-	hash_seq_init(&hstat, pgStatDBHash);
-	while ((dbentry = (PgStat_StatDBEntry *) hash_seq_search(&hstat)) != NULL)
-	{
-		Oid			dbid = dbentry->databaseid;
-
-		CHECK_FOR_INTERRUPTS();
-
-		/* the DB entry for shared tables (with InvalidOid) is never dropped */
-		if (OidIsValid(dbid) &&
-			hash_search(htab, (void *) &dbid, HASH_FIND, NULL) == NULL)
-			pgstat_drop_database(dbid);
-	}
-
-	/* Clean up */
-	hash_destroy(htab);
-
-	/*
-	 * Lookup our own database entry; if not found, nothing more to do.
-	 */
-	dbentry = (PgStat_StatDBEntry *) hash_search(pgStatDBHash,
-												 (void *) &MyDatabaseId,
-												 HASH_FIND, NULL);
-	if (dbentry == NULL || dbentry->tables == NULL)
-		return;
-
-	/*
-	 * Similarly to above, make a list of all known relations in this DB.
-	 */
-	htab = pgstat_collect_oids(RelationRelationId, Anum_pg_class_oid);
-
-	/*
-	 * Initialize our messages table counter to zero
-	 */
-	msg.m_nentries = 0;
-
-	/*
-	 * Check for all tables listed in stats hashtable if they still exist.
-	 */
-	hash_seq_init(&hstat, dbentry->tables);
-	while ((tabentry = (PgStat_StatTabEntry *) hash_seq_search(&hstat)) != NULL)
+	dshash_seq_status hstat;
+	PgStatHashEntry *p;
+	int			listlen = 16;
+	PgStatEnvelope **envlist = palloc(sizeof(PgStatEnvelope * *) * listlen);
+	int			n = 0;
+
+	dshash_seq_init(&hstat, pgStatSharedHash, false);
+	while ((p = dshash_seq_next(&hstat)) != NULL)
 	{
-		Oid			tabid = tabentry->tableid;
-
-		CHECK_FOR_INTERRUPTS();
-
-		if (hash_search(htab, (void *) &tabid, HASH_FIND, NULL) != NULL)
+		if ((type != PGSTAT_TYPE_ALL && p->key.type != type) ||
+			(type != PGSTAT_TYPE_DB && p->key.databaseid != dbid))
 			continue;
 
-		/*
-		 * Not there, so add this table's Oid to the message
-		 */
-		msg.m_tableid[msg.m_nentries++] = tabid;
-
-		/*
-		 * If the message is full, send it out and reinitialize to empty
-		 */
-		if (msg.m_nentries >= PGSTAT_NUM_TABPURGE)
+		if (n >= listlen - 1)
 		{
-			len = offsetof(PgStat_MsgTabpurge, m_tableid[0])
-				+ msg.m_nentries * sizeof(Oid);
-
-			pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_TABPURGE);
-			msg.m_databaseid = MyDatabaseId;
-			pgstat_send(&msg, len);
-
-			msg.m_nentries = 0;
+			listlen *= 2;
+			envlist = repalloc(envlist, listlen * sizeof(PgStatEnvelope * *));
 		}
+		envlist[n++] = dsa_get_address(area, p->env);
 	}
+	dshash_seq_term(&hstat);
 
-	/*
-	 * Send the rest
-	 */
-	if (msg.m_nentries > 0)
-	{
-		len = offsetof(PgStat_MsgTabpurge, m_tableid[0])
-			+ msg.m_nentries * sizeof(Oid);
-
-		pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_TABPURGE);
-		msg.m_databaseid = MyDatabaseId;
-		pgstat_send(&msg, len);
-	}
-
-	/* Clean up */
-	hash_destroy(htab);
-
-	/*
-	 * Now repeat the above steps for functions.  However, we needn't bother
-	 * in the common case where no function stats are being collected.
-	 */
-	if (dbentry->functions != NULL &&
-		hash_get_num_entries(dbentry->functions) > 0)
-	{
-		htab = pgstat_collect_oids(ProcedureRelationId, Anum_pg_proc_oid);
-
-		pgstat_setheader(&f_msg.m_hdr, PGSTAT_MTYPE_FUNCPURGE);
-		f_msg.m_databaseid = MyDatabaseId;
-		f_msg.m_nentries = 0;
-
-		hash_seq_init(&hstat, dbentry->functions);
-		while ((funcentry = (PgStat_StatFuncEntry *) hash_seq_search(&hstat)) != NULL)
-		{
-			Oid			funcid = funcentry->functionid;
-
-			CHECK_FOR_INTERRUPTS();
+	envlist[n] = NULL;
 
-			if (hash_search(htab, (void *) &funcid, HASH_FIND, NULL) != NULL)
-				continue;
-
-			/*
-			 * Not there, so add this function's Oid to the message
-			 */
-			f_msg.m_functionid[f_msg.m_nentries++] = funcid;
-
-			/*
-			 * If the message is full, send it out and reinitialize to empty
-			 */
-			if (f_msg.m_nentries >= PGSTAT_NUM_FUNCPURGE)
-			{
-				len = offsetof(PgStat_MsgFuncpurge, m_functionid[0])
-					+ f_msg.m_nentries * sizeof(Oid);
-
-				pgstat_send(&f_msg, len);
-
-				f_msg.m_nentries = 0;
-			}
-		}
-
-		/*
-		 * Send the rest
-		 */
-		if (f_msg.m_nentries > 0)
-		{
-			len = offsetof(PgStat_MsgFuncpurge, m_functionid[0])
-				+ f_msg.m_nentries * sizeof(Oid);
-
-			pgstat_send(&f_msg, len);
-		}
-
-		hash_destroy(htab);
-	}
+	return envlist;
 }

 /* ----------
- * pgstat_collect_oids() -
+ * collect_oids() -
  *
  *	Collect the OIDs of all objects listed in the specified system catalog
  *	into a temporary hash table.  Caller should hash_destroy the result
@@ -1198,7 +1186,7 @@ pgstat_vacuum_stat(void)
  * ----------
  */
 static HTAB *
-pgstat_collect_oids(Oid catalogid, AttrNumber anum_oid)
+collect_oids(Oid catalogid, AttrNumber anum_oid)
 {
 	HTAB	   *htab;
 	HASHCTL		hash_ctl;
@@ -1212,7 +1200,7 @@ pgstat_collect_oids(Oid catalogid, AttrNumber anum_oid)
 	hash_ctl.entrysize = sizeof(Oid);
 	hash_ctl.hcxt = CurrentMemoryContext;
 	htab = hash_create("Temporary table of OIDs",
-					   PGSTAT_TAB_HASH_SIZE,
+					   PGSTAT_TABLE_HASH_SIZE,
 					   &hash_ctl,
 					   HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
 
@@ -1239,65 +1227,184 @@ pgstat_collect_oids(Oid catalogid, AttrNumber anum_oid)
 }

+/* ----------
+ * pgstat_vacuum_stat() -
+ *
+ *  Delete shared stat entries that are not in system catalogs.
+ *
+ *  To avoid holding exclusive lock on dshash for a long time, the process is
+ *  performed in three steps.
+ *
+ *   1: Collect existent oids of every kind of object.
+ *   2: Collect victim entries by scanning with shared lock.
+ *   3: Try removing every nominated entry without waiting for lock.
+ *
+ *  As the consequence of the last step, some entries may be left alone due to
+ *  lock failure, but as explained by the comment of pgstat_vacuum_stat, they
+ *  will be deleted by later vacuums.
+ * ----------
+ */
+void
+pgstat_vacuum_stat(void)
+{
+	HTAB	   *dbids;			/* database ids */
+	HTAB	   *relids;			/* relation ids in the current database */
+	HTAB	   *funcids;		/* function ids in the current database */
+	PgStatEnvelope **victims;	/* victim entry list */
+	int			arraylen = 0;	/* storage size of the above */
+	int			nvictims = 0;	/* # of entries of the above */
+	dshash_seq_status dshstat;
+	PgStatHashEntry *ent;
+	int			i;
+
+	/* we don't collect stats under standalone mode */
+	if (!IsUnderPostmaster)
+		return;
+
+	/* collect oids of existent objects */
+	dbids = collect_oids(DatabaseRelationId, Anum_pg_database_oid);
+	relids = collect_oids(RelationRelationId, Anum_pg_class_oid);
+	funcids = collect_oids(ProcedureRelationId, Anum_pg_proc_oid);
+
+	/* collect victims from shared stats */
+	arraylen = 16;
+	victims = palloc(sizeof(PgStatEnvelope * *) * arraylen);
+	nvictims = 0;
+
+	dshash_seq_init(&dshstat, pgStatSharedHash, false);
+
+	while ((ent = dshash_seq_next(&dshstat)) != NULL)
+	{
+		HTAB	   *oidtab;
+		Oid		   *key;
+
+		CHECK_FOR_INTERRUPTS();
+
+		/*
+		 * Don't drop entries for other than database objects not of the
+		 * current database.
+		 */
+		if (ent->key.type != PGSTAT_TYPE_DB &&
+			ent->key.databaseid != MyDatabaseId)
+			continue;
+
+		switch (ent->key.type)
+		{
+			case PGSTAT_TYPE_DB:
+				/* don't remove database entry for shared tables */
+				if (ent->key.databaseid == 0)
+					continue;
+				oidtab = dbids;
+				key = &ent->key.databaseid;
+				break;
+
+			case PGSTAT_TYPE_TABLE:
+				oidtab = relids;
+				key = &ent->key.objectid;
+				break;
+
+			case PGSTAT_TYPE_FUNCTION:
+				oidtab = funcids;
+				key = &ent->key.objectid;
+				break;
+			case PGSTAT_TYPE_ALL:
+				Assert(false);
+				break;
+		}
+
+		/* Skip existent objects. */
+		if (hash_search(oidtab, key, HASH_FIND, NULL) != NULL)
+			continue;
+
+		/* extend the list if needed */
+		if (nvictims >= arraylen)
+		{
+			arraylen *= 2;
+			victims = repalloc(victims, sizeof(PgStatEnvelope * *) * arraylen);
+		}
+
+		victims[nvictims++] = dsa_get_address(area, ent->env);
+	}
+	dshash_seq_term(&dshstat);
+	hash_destroy(dbids);
+	hash_destroy(relids);
+	hash_destroy(funcids);
+
+	/* Now try removing the victim entries */
+	for (i = 0; i < nvictims; i++)
+	{
+		PgStatEnvelope *p = victims[i];
+
+		delete_stat_entry(p->type, p->databaseid, p->objectid, true);
+	}
+}
+
+
+/* ----------
+ * delete_stat_entry() -
+ *
+ *  Deletes the specified entry from shared stats hash.
+ *
+ *  Returns true when successfully deleted.
+ * ----------
+ */
+static bool
+delete_stat_entry(PgStatTypes type, Oid dbid, Oid objid, bool nowait)
+{
+	PgStatHashEntryKey key;
+	PgStatHashEntry *ent;
+
+	key.type = type;
+	key.databaseid = dbid;
+	key.objectid = objid;
+	ent = dshash_find_extended(pgStatSharedHash, &key,
+							   true, nowait, false, NULL);
+
+	if (!ent)
+		return false;			/* lock failed or not found */
+
+	/* The entry is exclusively locked, so we can free the chunk first. */
+	dsa_free(area, ent->env);
+	dshash_delete_entry(pgStatSharedHash, ent);
+
+	return true;
+}
+
+
 /* ----------
  * pgstat_drop_database() -
  *
- *	Tell the collector that we just dropped a database.
- *	(If the message gets lost, we will still clean the dead DB eventually
- *	via future invocations of pgstat_vacuum_stat().)
- * ----------
+ *	Remove entry for the database that we just dropped.
+ *
+ *  Some entries might be left alone due to lock failure or some stats are
+ *	flushed after this but we will still clean the dead DB eventually via
+ *	future invocations of pgstat_vacuum_stat().
+ *	----------
  */
 void
 pgstat_drop_database(Oid databaseid)
 {
-	PgStat_MsgDropdb msg;
+	PgStatEnvelope **envlist;
+	PgStatEnvelope **p;
 
-	if (pgStatSock == PGINVALID_SOCKET)
-		return;
-
-	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_DROPDB);
-	msg.m_databaseid = databaseid;
-	pgstat_send(&msg, sizeof(msg));
-}
-
-
-/* ----------
- * pgstat_drop_relation() -
- *
- *	Tell the collector that we just dropped a relation.
- *	(If the message gets lost, we will still clean the dead entry eventually
- *	via future invocations of pgstat_vacuum_stat().)
- *
- *	Currently not used for lack of any good place to call it; we rely
- *	entirely on pgstat_vacuum_stat() to clean out stats for dead rels.
- * ----------
- */
-#ifdef NOT_USED
-void
-pgstat_drop_relation(Oid relid)
-{
-	PgStat_MsgTabpurge msg;
-	int			len;
+	Assert(OidIsValid(databaseid));
 
-	if (pgStatSock == PGINVALID_SOCKET)
+	if (!IsUnderPostmaster || !pgStatSharedHash)
 		return;
 
-	msg.m_tableid[0] = relid;
-	msg.m_nentries = 1;
+	envlist = collect_stat_entries(PGSTAT_TYPE_ALL, MyDatabaseId);
 
-	len = offsetof(PgStat_MsgTabpurge, m_tableid[0]) + sizeof(Oid);
+	for (p = envlist; *p != NULL; p++)
+		delete_stat_entry((*p)->type, (*p)->databaseid, (*p)->objectid, true);
 
-	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_TABPURGE);
-	msg.m_databaseid = MyDatabaseId;
-	pgstat_send(&msg, len);
+	pfree(envlist);
 }
-#endif							/* NOT_USED */

 /* ----------
  * pgstat_reset_counters() -
  *
- *	Tell the statistics collector to reset counters for our database.
+ *	Reset counters for our database.
  *
  *	Permission checking for this function is managed through the normal
  *	GRANT system.
@@ -1306,20 +1413,47 @@ pgstat_drop_relation(Oid relid)
 void
 pgstat_reset_counters(void)
 {
-	PgStat_MsgResetcounter msg;
+	PgStatEnvelope **envlist;
+	PgStatEnvelope **p;
 
-	if (pgStatSock == PGINVALID_SOCKET)
-		return;
+	/* Lookup the entries of the current database in the stats hash. */
+	envlist = collect_stat_entries(PGSTAT_TYPE_ALL, MyDatabaseId);
+	for (p = envlist; *p != NULL; p++)
+	{
+		PgStatEnvelope *env = *p;
+		PgStat_StatDBEntry *dbstat;
 
-	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RESETCOUNTER);
-	msg.m_databaseid = MyDatabaseId;
-	pgstat_send(&msg, sizeof(msg));
+		LWLockAcquire(&env->lock, LW_EXCLUSIVE);
+
+		switch (env->type)
+		{
+			case PGSTAT_TYPE_TABLE:
+				init_tabentry(env);
+				break;
+
+			case PGSTAT_TYPE_FUNCTION:
+				init_funcentry(env);
+				break;
+
+			case PGSTAT_TYPE_DB:
+				init_dbentry(env);
+				dbstat = (PgStat_StatDBEntry *) &env->body;
+				dbstat->stat_reset_timestamp = GetCurrentTimestamp();
+				break;
+			default:
+				Assert(false);
+		}
+
+		LWLockRelease(&env->lock);
+	}
+
+	pfree(envlist);
 }
 
 /* ----------
  * pgstat_reset_shared_counters() -
  *
- *	Tell the statistics collector to reset cluster-wide shared counters.
+ *	Reset cluster-wide shared counters.
  *
  *	Permission checking for this function is managed through the normal
  *	GRANT system.
@@ -1328,29 +1462,37 @@ pgstat_reset_counters(void)
 void
 pgstat_reset_shared_counters(const char *target)
 {
-	PgStat_MsgResetsharedcounter msg;
-
-	if (pgStatSock == PGINVALID_SOCKET)
-		return;
-
+	/* Reset the archiver statistics for the cluster. */
 	if (strcmp(target, "archiver") == 0)
-		msg.m_resettarget = RESET_ARCHIVER;
+	{
+		TimestampTz now = GetCurrentTimestamp();
+
+		LWLockAcquire(StatsLock, LW_EXCLUSIVE);
+		MemSet(shared_archiverStats, 0, sizeof(*shared_archiverStats));
+		shared_archiverStats->stat_reset_timestamp = now;
+		LWLockRelease(StatsLock);
+	}
+	/* Reset the bgwriter statistics for the cluster. */
 	else if (strcmp(target, "bgwriter") == 0)
-		msg.m_resettarget = RESET_BGWRITER;
+	{
+		TimestampTz now = GetCurrentTimestamp();
+
+		LWLockAcquire(StatsLock, LW_EXCLUSIVE);
+		MemSet(shared_globalStats, 0, sizeof(*shared_globalStats));
+		shared_globalStats->stat_reset_timestamp = now;
+		LWLockRelease(StatsLock);
+	}
 	else
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 				 errmsg("unrecognized reset target: \"%s\"", target),
 				 errhint("Target must be \"archiver\" or \"bgwriter\".")));
-
-	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RESETSHAREDCOUNTER);
-	pgstat_send(&msg, sizeof(msg));
 }
 
 /* ----------
  * pgstat_reset_single_counter() -
  *
- *	Tell the statistics collector to reset a single counter.
+ *	Reset a single counter.
  *
  *	Permission checking for this function is managed through the normal
  *	GRANT system.
@@ -1359,17 +1501,42 @@ pgstat_reset_shared_counters(const char *target)
 void
 pgstat_reset_single_counter(Oid objoid, PgStat_Single_Reset_Type type)
 {
-	PgStat_MsgResetsinglecounter msg;
+	PgStatEnvelope *env;
+	PgStat_StatDBEntry *dbentry;
+	PgStatTypes stattype;
+	TimestampTz ts;
 
-	if (pgStatSock == PGINVALID_SOCKET)
-		return;
+	env = get_stat_entry(PGSTAT_TYPE_DB, MyDatabaseId, InvalidOid,
+						 false, NULL, NULL);
+	Assert(env);
 
-	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RESETSINGLECOUNTER);
-	msg.m_databaseid = MyDatabaseId;
-	msg.m_resettype = type;
-	msg.m_objectid = objoid;
+	/* Set the reset timestamp for the whole database */
+	dbentry = (PgStat_StatDBEntry *) &env->body;
+	ts = GetCurrentTimestamp();
+	LWLockAcquire(&env->lock, LW_EXCLUSIVE);
+	dbentry->stat_reset_timestamp = ts;
+	LWLockRelease(&env->lock);
 
-	pgstat_send(&msg, sizeof(msg));
+	/* Remove object if it exists, ignore if not */
+	switch (type)
+	{
+		case RESET_TABLE:
+			stattype = PGSTAT_TYPE_TABLE;
+			break;
+		case RESET_FUNCTION:
+			stattype = PGSTAT_TYPE_FUNCTION;
+	}
+
+	env = get_stat_entry(stattype, MyDatabaseId, objoid, false, NULL, NULL);
+	LWLockAcquire(&env->lock, LW_EXCLUSIVE);
+	if (env->type == PGSTAT_TYPE_TABLE)
+		init_tabentry(env);
+	else
+	{
+		Assert(env->type == PGSTAT_TYPE_FUNCTION);
+		init_funcentry(env);
+	}
+	LWLockRelease(&env->lock);
 }
 
 /* ----------
@@ -1383,48 +1550,63 @@ pgstat_reset_single_counter(Oid objoid, PgStat_Single_Reset_Type type)
 void
 pgstat_report_autovac(Oid dboid)
 {
-	PgStat_MsgAutovacStart msg;
+	PgStat_StatDBEntry *dbentry;
+	TimestampTz ts;
 
-	if (pgStatSock == PGINVALID_SOCKET)
+	/* return if activity stats is not active */
+	if (!area)
 		return;
 
-	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_AUTOVAC_START);
-	msg.m_databaseid = dboid;
-	msg.m_start_time = GetCurrentTimestamp();
+	ts = GetCurrentTimestamp();
 
-	pgstat_send(&msg, sizeof(msg));
+	/*
+	 * Store the last autovacuum time in the database's hash table entry.
+	 */
+	dbentry = get_local_dbstat_entry(dboid);
+	dbentry->last_autovac_time = ts;
 }

 /* ---------
  * pgstat_report_vacuum() -
  *
- *	Tell the collector about the table we just vacuumed.
+ *	Report about the table we just vacuumed.
  * ---------
  */
 void
 pgstat_report_vacuum(Oid tableoid, bool shared,
 					 PgStat_Counter livetuples, PgStat_Counter deadtuples)
 {
-	PgStat_MsgVacuum msg;
+	PgStat_TableStatus *tabentry;
+	TimestampTz ts;
 
-	if (pgStatSock == PGINVALID_SOCKET || !pgstat_track_counts)
+	/* return if we are not collecting stats */
+	if (!area)
 		return;
 
-	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_VACUUM);
-	msg.m_databaseid = shared ? InvalidOid : MyDatabaseId;
-	msg.m_tableoid = tableoid;
-	msg.m_autovacuum = IsAutoVacuumWorkerProcess();
-	msg.m_vacuumtime = GetCurrentTimestamp();
-	msg.m_live_tuples = livetuples;
-	msg.m_dead_tuples = deadtuples;
-	pgstat_send(&msg, sizeof(msg));
+	/* Store the data in the table's hash table entry. */
+	ts = GetCurrentTimestamp();
+	tabentry = get_local_tabstat_entry(tableoid, shared);
+
+	tabentry->t_counts.t_delta_live_tuples = livetuples;
+	tabentry->t_counts.t_delta_dead_tuples = deadtuples;
+
+	if (IsAutoVacuumWorkerProcess())
+	{
+		tabentry->autovac_vacuum_timestamp = ts;
+		tabentry->t_counts.autovac_vacuum_count++;
+	}
+	else
+	{
+		tabentry->vacuum_timestamp = ts;
+		tabentry->t_counts.vacuum_count++;
+	}
 }
 
 /* --------
  * pgstat_report_analyze() -
  *
- *	Tell the collector about the table we just analyzed.
+ *	Report about the table we just analyzed.
  *
  * Caller must provide new live- and dead-tuples estimates, as well as a
  * flag indicating whether to reset the changes_since_analyze counter.
@@ -1435,9 +1617,10 @@ pgstat_report_analyze(Relation rel,
 					  PgStat_Counter livetuples, PgStat_Counter deadtuples,
 					  bool resetcounter)
 {
-	PgStat_MsgAnalyze msg;
+	PgStat_TableStatus *tabentry;
 
-	if (pgStatSock == PGINVALID_SOCKET || !pgstat_track_counts)
+	/* return if we are not collecting stats */
+	if (!area)
 		return;
 
 	/*
@@ -1445,10 +1628,10 @@ pgstat_report_analyze(Relation rel,
 	 * already inserted and/or deleted rows in the target table. ANALYZE will
 	 * have counted such rows as live or dead respectively. Because we will
 	 * report our counts of such rows at transaction end, we should subtract
-	 * off these counts from what we send to the collector now, else they'll
-	 * be double-counted after commit.  (This approach also ensures that the
-	 * collector ends up with the right numbers if we abort instead of
-	 * committing.)
+	 * off these counts from what is already written to shared stats now, else
+	 * they'll be double-counted after commit.  (This approach also ensures
+	 * that the shared stats ends up with the right numbers if we abort
+	 * instead of committing.)
 	 */
 	if (rel->pgstat_info != NULL)
 	{
@@ -1466,158 +1649,172 @@ pgstat_report_analyze(Relation rel,
 		deadtuples = Max(deadtuples, 0);
 	}
 
-	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_ANALYZE);
-	msg.m_databaseid = rel->rd_rel->relisshared ? InvalidOid : MyDatabaseId;
-	msg.m_tableoid = RelationGetRelid(rel);
-	msg.m_autovacuum = IsAutoVacuumWorkerProcess();
-	msg.m_resetcounter = resetcounter;
-	msg.m_analyzetime = GetCurrentTimestamp();
-	msg.m_live_tuples = livetuples;
-	msg.m_dead_tuples = deadtuples;
-	pgstat_send(&msg, sizeof(msg));
+	/* Store the data in the table's hash table entry. */
+	tabentry = get_local_tabstat_entry(RelationGetRelid(rel),
+									   rel->rd_rel->relisshared);
+
+	tabentry->t_counts.t_delta_live_tuples = livetuples;
+	tabentry->t_counts.t_delta_dead_tuples = deadtuples;
+
+	/*
+	 * If commanded, reset changes_since_analyze to zero.  This forgets any
+	 * changes that were committed while the ANALYZE was in progress, but we
+	 * have no good way to estimate how many of those there were.
+	 */
+	if (resetcounter)
+		tabentry->t_counts.reset_changed_tuples = true;
+
+	if (IsAutoVacuumWorkerProcess())
+	{
+		tabentry->autovac_analyze_timestamp = GetCurrentTimestamp();
+		tabentry->t_counts.autovac_analyze_count++;
+	}
+	else
+	{
+		tabentry->analyze_timestamp = GetCurrentTimestamp();
+		tabentry->t_counts.analyze_count++;
+	}
 }
 
 /* --------
  * pgstat_report_recovery_conflict() -
  *
- *	Tell the collector about a Hot Standby recovery conflict.
+ *	Report a Hot Standby recovery conflict.
  * --------
  */
 void
 pgstat_report_recovery_conflict(int reason)
 {
-	PgStat_MsgRecoveryConflict msg;
+	PgStat_StatDBEntry *dbent;
 
-	if (pgStatSock == PGINVALID_SOCKET || !pgstat_track_counts)
+	/* return if we are not collecting stats */
+	if (!area)
 		return;
 
-	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RECOVERYCONFLICT);
-	msg.m_databaseid = MyDatabaseId;
-	msg.m_reason = reason;
-	pgstat_send(&msg, sizeof(msg));
+	dbent = get_local_dbstat_entry(MyDatabaseId);
+
+	switch (reason)
+	{
+		case PROCSIG_RECOVERY_CONFLICT_DATABASE:
+
+			/*
+			 * Since we drop the information about the database as soon as it
+			 * replicates, there is no point in counting these conflicts.
+			 */
+			break;
+		case PROCSIG_RECOVERY_CONFLICT_TABLESPACE:
+			dbent->counts.n_conflict_tablespace++;
+			break;
+		case PROCSIG_RECOVERY_CONFLICT_LOCK:
+			dbent->counts.n_conflict_lock++;
+			break;
+		case PROCSIG_RECOVERY_CONFLICT_SNAPSHOT:
+			dbent->counts.n_conflict_snapshot++;
+			break;
+		case PROCSIG_RECOVERY_CONFLICT_BUFFERPIN:
+			dbent->counts.n_conflict_bufferpin++;
+			break;
+		case PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK:
+			dbent->counts.n_conflict_startup_deadlock++;
+			break;
+	}
 }
 
 /* --------
  * pgstat_report_deadlock() -
  *
- *	Tell the collector about a deadlock detected.
+ *	Report a deadlock detected.
  * --------
  */
 void
 pgstat_report_deadlock(void)
 {
-	PgStat_MsgDeadlock msg;
+	PgStat_StatDBEntry *dbent;
 
-	if (pgStatSock == PGINVALID_SOCKET || !pgstat_track_counts)
+	/* return if we are not collecting stats */
+	if (!area)
 		return;
 
-	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_DEADLOCK);
-	msg.m_databaseid = MyDatabaseId;
-	pgstat_send(&msg, sizeof(msg));
-}
-
-
-
-/* --------
- * pgstat_report_checksum_failures_in_db() -
- *
- *	Tell the collector about one or more checksum failures.
- * --------
- */
-void
-pgstat_report_checksum_failures_in_db(Oid dboid, int failurecount)
-{
-	PgStat_MsgChecksumFailure msg;
-
-	if (pgStatSock == PGINVALID_SOCKET || !pgstat_track_counts)
-		return;
-
-	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_CHECKSUMFAILURE);
-	msg.m_databaseid = dboid;
-	msg.m_failurecount = failurecount;
-	msg.m_failure_time = GetCurrentTimestamp();
-
-	pgstat_send(&msg, sizeof(msg));
+	dbent = get_local_dbstat_entry(MyDatabaseId);
+	dbent->counts.n_deadlocks++;
 }
 
 /* --------
  * pgstat_report_checksum_failure() -
  *
- *	Tell the collector about a checksum failure.
+ *	Reports about a checksum failure.
  * --------
  */
 void
 pgstat_report_checksum_failure(void)
 {
-	pgstat_report_checksum_failures_in_db(MyDatabaseId, 1);
+	PgStat_StatDBEntry *dbent;
+
+	/* return if we are not collecting stats */
+	if (!area)
+		return;
+
+	dbent = get_local_dbstat_entry(MyDatabaseId);
+	dbent->counts.n_checksum_failures++;
 }
 
 /* --------
  * pgstat_report_tempfile() -
  *
- *	Tell the collector about a temporary file.
+ *	Report a temporary file.
  * --------
  */
 void
 pgstat_report_tempfile(size_t filesize)
 {
-	PgStat_MsgTempFile msg;
+	PgStat_StatDBEntry *dbent;
 
-	if (pgStatSock == PGINVALID_SOCKET || !pgstat_track_counts)
+	/* return if we are not collecting stats */
+	if (!area)
 		return;
 
-	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_TEMPFILE);
-	msg.m_databaseid = MyDatabaseId;
-	msg.m_filesize = filesize;
-	pgstat_send(&msg, sizeof(msg));
+	if (filesize == 0)			/* Is there a case where filesize is really 0? */
+		return;
+
+	dbent = get_local_dbstat_entry(MyDatabaseId);
+	dbent->counts.n_temp_bytes += filesize; /* needs check overflow */
+	dbent->counts.n_temp_files++;
 }

-/* ----------
- * pgstat_ping() -
+/* --------
+ * pgstat_report_checksum_failures_in_db(dboid, failure_count) -
  *
- *	Send some junk data to the collector to increase traffic.
- * ----------
+ *	Reports about one or more checksum failures.
+ * --------
  */
 void
-pgstat_ping(void)
+pgstat_report_checksum_failures_in_db(Oid dboid, int failurecount)
 {
-	PgStat_MsgDummy msg;
+	PgStat_StatDBEntry *dbentry;
 
-	if (pgStatSock == PGINVALID_SOCKET)
+	/* return if we are not active */
+	if (!area)
 		return;
 
-	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_DUMMY);
-	pgstat_send(&msg, sizeof(msg));
+	dbentry = get_local_dbstat_entry(dboid);
+
+	/* add accumulated count to the parameter */
+	dbentry->counts.n_checksum_failures += failurecount;
 }
 
 /* ----------
- * pgstat_send_inquiry() -
+ * pgstat_init_function_usage() -
  *
- *	Notify collector that we need fresh data.
+ *  Initialize function call usage data.
+ *  Called by the executor before invoking a function.
  * ----------
  */
-static void
-pgstat_send_inquiry(TimestampTz clock_time, TimestampTz cutoff_time, Oid databaseid)
-{
-	PgStat_MsgInquiry msg;
-
-	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_INQUIRY);
-	msg.clock_time = clock_time;
-	msg.cutoff_time = cutoff_time;
-	msg.databaseid = databaseid;
-	pgstat_send(&msg, sizeof(msg));
-}
-
-
-/*
- * Initialize function call usage data.
- * Called by the executor before invoking a function.
- */
 void
 pgstat_init_function_usage(FunctionCallInfo fcinfo,
 						   PgStat_FunctionCallUsage *fcu)
 {
+	PgStatEnvelope *env;
 	PgStat_BackendFunctionEntry *htabent;
 	bool		found;
 
@@ -1628,26 +1825,15 @@ pgstat_init_function_usage(FunctionCallInfo fcinfo,
 		return;
 	}
 
-	if (!pgStatFunctions)
-	{
-		/* First time through - initialize function stat table */
-		HASHCTL		hash_ctl;
+	env = get_local_stat_entry(PGSTAT_TYPE_FUNCTION, MyDatabaseId,
+							   fcinfo->flinfo->fn_oid, true, &found);
+	htabent = (PgStat_BackendFunctionEntry *) &env->body;
 
-		memset(&hash_ctl, 0, sizeof(hash_ctl));
-		hash_ctl.keysize = sizeof(Oid);
-		hash_ctl.entrysize = sizeof(PgStat_BackendFunctionEntry);
-		pgStatFunctions = hash_create("Function stat entries",
-									  PGSTAT_FUNCTION_HASH_SIZE,
-									  &hash_ctl,
-									  HASH_ELEM | HASH_BLOBS);
-	}
-
-	/* Get the stats entry for this function, create if necessary */
-	htabent = hash_search(pgStatFunctions, &fcinfo->flinfo->fn_oid,
-						  HASH_ENTER, &found);
 	if (!found)
 		MemSet(&htabent->f_counts, 0, sizeof(PgStat_FunctionCounts));
 
+	htabent->f_id = fcinfo->flinfo->fn_oid;
+
 	fcu->fs = &htabent->f_counts;
 
 	/* save stats for this function, later used to compensate for recursion */
@@ -1660,31 +1846,38 @@ pgstat_init_function_usage(FunctionCallInfo fcinfo,
 	INSTR_TIME_SET_CURRENT(fcu->f_start);
 }
 
-/*
- * find_funcstat_entry - find any existing PgStat_BackendFunctionEntry entry
- *		for specified function
+/* ----------
+ * find_funcstat_entry() -
  *
- * If no entry, return NULL, don't create a new one
+ *  find any existing PgStat_BackendFunctionEntry entry for specified function
+ *
+ *  If no entry, return NULL, not creating a new one.
+ * ----------
  */
 PgStat_BackendFunctionEntry *
 find_funcstat_entry(Oid func_id)
 {
-	if (pgStatFunctions == NULL)
+	PgStatEnvelope *env;
+
+	env = get_local_stat_entry(PGSTAT_TYPE_FUNCTION, MyDatabaseId,
+							   func_id, false, NULL);
+	if (!env)
 		return NULL;
 
-	return (PgStat_BackendFunctionEntry *) hash_search(pgStatFunctions,
-													   (void *) &func_id,
-													   HASH_FIND, NULL);
+	return (PgStat_BackendFunctionEntry *) &env->body;
 }
 
-/*
- * Calculate function call usage and update stat counters.
- * Called by the executor after invoking a function.
+/* ----------
+ * pgstat_end_function_usage() -
  *
- * In the case of a set-returning function that runs in value-per-call mode,
- * we will see multiple pgstat_init_function_usage/pgstat_end_function_usage
- * calls for what the user considers a single call of the function.  The
- * finalize flag should be TRUE on the last call.
+ *  Calculate function call usage and update stat counters.
+ *  Called by the executor after invoking a function.
+ *
+ *  In the case of a set-returning function that runs in value-per-call mode,
+ *  we will see multiple pgstat_init_function_usage/pgstat_end_function_usage
+ *  calls for what the user considers a single call of the function.  The
+ *  finalize flag should be TRUE on the last call.
+ * ----------
  */
 void
 pgstat_end_function_usage(PgStat_FunctionCallUsage *fcu, bool finalize)
@@ -1725,9 +1918,6 @@ pgstat_end_function_usage(PgStat_FunctionCallUsage *fcu, bool finalize)
 		fs->f_numcalls++;
 	fs->f_total_time = f_total;
 	INSTR_TIME_ADD(fs->f_self_time, f_self);
-
-	/* indicate that we have something to send */
-	have_function_stats = true;
 }

@@ -1739,8 +1929,7 @@ pgstat_end_function_usage(PgStat_FunctionCallUsage *fcu, bool finalize)
  *
  *	We assume that a relcache entry's pgstat_info field is zeroed by
  *	relcache.c when the relcache entry is made; thereafter it is long-lived
- *	data.  We can avoid repeated searches of the TabStatus arrays when the
- *	same relation is touched repeatedly within a transaction.
+ *	data.
  * ----------
  */
 void
@@ -1760,7 +1949,8 @@ pgstat_initstats(Relation rel)
 		return;
 	}
 
-	if (pgStatSock == PGINVALID_SOCKET || !pgstat_track_counts)
+	/* return if we are not collecting stats */
+	if (!area)
 	{
 		/* We're not counting at all */
 		rel->pgstat_info = NULL;
@@ -1776,116 +1966,157 @@ pgstat_initstats(Relation rel)
 		return;
 
 	/* Else find or make the PgStat_TableStatus entry, and update link */
-	rel->pgstat_info = get_tabstat_entry(rel_id, rel->rd_rel->relisshared);
+	rel->pgstat_info = get_local_tabstat_entry(rel_id, rel->rd_rel->relisshared);
 }
 
-/*
- * get_tabstat_entry - find or create a PgStat_TableStatus entry for rel
+
+/* ----------
+ * get_local_stat_entry() -
+ *
+ *  Returns local stats entry for the type, dbid and objid.
+ *  If create is true, new entry is created if not yet.  found must be non-null
+ *  in the case.
+ *
+ *
+ *  The caller is responsible to initialize body part of the returned envelope.
+ * ----------
  */
-static PgStat_TableStatus *
-get_tabstat_entry(Oid rel_id, bool isshared)
+static PgStatEnvelope *
+get_local_stat_entry(PgStatTypes type, Oid dbid, Oid objid,
+					 bool create, bool *found)
 {
-	TabStatHashEntry *hash_entry;
-	PgStat_TableStatus *entry;
-	TabStatusArray *tsa;
-	bool		found;
+	PgStatHashEntryKey key;
+	PgStatLocalHashEntry *entry;
 
-	/*
-	 * Create hash table if we don't have it already.
-	 */
-	if (pgStatTabHash == NULL)
+	if (pgStatLocalHash == NULL)
 	{
 		HASHCTL		ctl;
 
-		memset(&ctl, 0, sizeof(ctl));
-		ctl.keysize = sizeof(Oid);
-		ctl.entrysize = sizeof(TabStatHashEntry);
-
-		pgStatTabHash = hash_create("pgstat TabStatusArray lookup hash table",
-									TABSTAT_QUANTUM,
-									&ctl,
-									HASH_ELEM | HASH_BLOBS);
+		MemSet(&ctl, 0, sizeof(ctl));
+		ctl.keysize = sizeof(PgStatHashEntryKey);
+		ctl.entrysize = sizeof(PgStatLocalHashEntry);
+
+		pgStatLocalHash = hash_create("Local stat entries",
+									  PGSTAT_TABLE_HASH_SIZE,
+									  &ctl,
+									  HASH_ELEM | HASH_BLOBS);
+	}
+
+	/* Find an entry or create a new one. */
+	key.type = type;
+	key.databaseid = dbid;
+	key.objectid = objid;
+	entry = hash_search(pgStatLocalHash, &key,
+						create ? HASH_ENTER : HASH_FIND, found);
+
+	if (!create && !entry)
+		return NULL;
+
+	if (create && !*found)
+	{
+		int			len = pgstat_localentsize[type];
+
+		entry->env = MemoryContextAlloc(CacheMemoryContext,
+										PgStatEnvelopeSize(len));
+		entry->env->type = type;
+		entry->env->len = len;
 	}
 
+	return entry->env;
+}
+
+/* ----------
+ * get_local_dbstat_entry() -
+ *
+ *  Find or create a local PgStat_StatDBEntry entry for dbid.  New entry is
+ *  created and initialized if not exists.
+ */
+static PgStat_StatDBEntry *
+get_local_dbstat_entry(Oid dbid)
+{
+	PgStatEnvelope *env;
+	PgStat_StatDBEntry *dbentry;
+	bool		found;
+
 	/*
 	 * Find an entry or create a new one.
 	 */
-	hash_entry = hash_search(pgStatTabHash, &rel_id, HASH_ENTER, &found);
+	env = get_local_stat_entry(PGSTAT_TYPE_DB, dbid, InvalidOid,
+							   true, &found);
+	dbentry = (PgStat_StatDBEntry *) &env->body;
+
 	if (!found)
 	{
-		/* initialize new entry with null pointer */
-		hash_entry->tsa_entry = NULL;
+		dbentry->databaseid = dbid;
+		dbentry->last_autovac_time = 0;
+		dbentry->last_checksum_failure = 0;
+		dbentry->stat_reset_timestamp = 0;
+		dbentry->stats_timestamp = 0;
+		MemSet(&dbentry->counts, 0, sizeof(PgStat_StatDBCounts));
 	}
 
-	/*
-	 * If entry is already valid, we're done.
-	 */
-	if (hash_entry->tsa_entry)
-		return hash_entry->tsa_entry;
-
-	/*
-	 * Locate the first pgStatTabList entry with free space, making a new list
-	 * entry if needed.  Note that we could get an OOM failure here, but if so
-	 * we have left the hashtable and the list in a consistent state.
-	 */
-	if (pgStatTabList == NULL)
-	{
-		/* Set up first pgStatTabList entry */
-		pgStatTabList = (TabStatusArray *)
-			MemoryContextAllocZero(TopMemoryContext,
-								   sizeof(TabStatusArray));
-	}
+	return dbentry;
+}
 
-	tsa = pgStatTabList;
-	while (tsa->tsa_used >= TABSTAT_QUANTUM)
-	{
-		if (tsa->tsa_next == NULL)
-			tsa->tsa_next = (TabStatusArray *)
-				MemoryContextAllocZero(TopMemoryContext,
-									   sizeof(TabStatusArray));
-		tsa = tsa->tsa_next;
-	}
 
-	/*
-	 * Allocate a PgStat_TableStatus entry within this list entry.  We assume
-	 * the entry was already zeroed, either at creation or after last use.
-	 */
-	entry = &tsa->tsa_entries[tsa->tsa_used++];
-	entry->t_id = rel_id;
-	entry->t_shared = isshared;
+/* ----------
+ * get_local_tabstat_entry() -
+ *  Find or create a PgStat_TableStatus entry for rel. New entry is created and
+ *  initialized if not exists.
+ * ----------
+ */
+static PgStat_TableStatus *
+get_local_tabstat_entry(Oid rel_id, bool isshared)
+{
+	PgStatEnvelope *env;
+	PgStat_TableStatus *tabentry;
+	bool		found;
 
-	/*
-	 * Now we can fill the entry in pgStatTabHash.
-	 */
-	hash_entry->tsa_entry = entry;
+	env = get_local_stat_entry(PGSTAT_TYPE_TABLE,
+							   isshared ? InvalidOid : MyDatabaseId,
+							   rel_id, true, &found);
 
-	return entry;
+	tabentry = (PgStat_TableStatus *) &env->body;
+
+	if (!found)
+	{
+		tabentry->t_id = rel_id;
+		tabentry->t_shared = isshared;
+		tabentry->trans = NULL;
+		MemSet(&tabentry->t_counts, 0, sizeof(PgStat_TableCounts));
+		tabentry->vacuum_timestamp = 0;
+		tabentry->autovac_vacuum_timestamp = 0;
+		tabentry->analyze_timestamp = 0;
+		tabentry->autovac_analyze_timestamp = 0;
+	}
+
+	return tabentry;
 }
 
+
 /*
  * find_tabstat_entry - find any existing PgStat_TableStatus entry for rel
  *
- * If no entry, return NULL, don't create a new one
+ *  Find any existing PgStat_TableStatus entry for rel from the current
+ *  database then from shared tables.
  *
- * Note: if we got an error in the most recent execution of pgstat_report_stat,
- * it's possible that an entry exists but there's no hashtable entry for it.
- * That's okay, we'll treat this case as "doesn't exist".
+ *  If no entry, return NULL, don't create a new one
+ * ----------
  */
 PgStat_TableStatus *
 find_tabstat_entry(Oid rel_id)
 {
-	TabStatHashEntry *hash_entry;
+	PgStatEnvelope *env;
 
-	/* If hashtable doesn't exist, there are no entries at all */
-	if (!pgStatTabHash)
-		return NULL;
+	env = get_local_stat_entry(PGSTAT_TYPE_TABLE, MyDatabaseId, rel_id,
+							   false, NULL);
+	if (!env)
+		env = get_local_stat_entry(PGSTAT_TYPE_TABLE, InvalidOid, rel_id,
+								   false, NULL);
+	if (env)
+		return (PgStat_TableStatus *) &env->body;
 
-	hash_entry = hash_search(pgStatTabHash, &rel_id, HASH_FIND, NULL);
-	if (!hash_entry)
-		return NULL;
-
-	/* Note that this step could also return NULL, but that's correct */
-	return hash_entry->tsa_entry;
+	return NULL;
 }
 
 /*
@@ -2362,7 +2593,7 @@ pgstat_twophase_postcommit(TransactionId xid, uint16 info,
 	PgStat_TableStatus *pgstat_info;
 
 	/* Find or create a tabstat entry for the rel */
-	pgstat_info = get_tabstat_entry(rec->t_id, rec->t_shared);
+	pgstat_info = get_local_tabstat_entry(rec->t_id, rec->t_shared);
 
 	/* Same math as in AtEOXact_PgStat, commit case */
 	pgstat_info->t_counts.t_tuples_inserted += rec->tuples_inserted;
@@ -2398,7 +2629,7 @@ pgstat_twophase_postabort(TransactionId xid, uint16 info,
 	PgStat_TableStatus *pgstat_info;
 
 	/* Find or create a tabstat entry for the rel */
-	pgstat_info = get_tabstat_entry(rec->t_id, rec->t_shared);
+	pgstat_info = get_local_tabstat_entry(rec->t_id, rec->t_shared);
 
 	/* Same math as in AtEOXact_PgStat, abort case */
 	if (rec->t_truncated)
@@ -2415,88 +2646,176 @@ pgstat_twophase_postabort(TransactionId xid, uint16 info,
 }

+/* ----------
+ * snapshot_statentry() -
+ *
+ *  Common routine for functions pgstat_fetch_stat_*entry()
+ *
+ *  Returns the pointer to the snapshot of the shared entry for the key or NULL
+ *  if not found. Returned snapshots are stable during the current transaction
+ *  or until pgstat_clear_snapshot() is called.
+ *
+ *  Created snapshots are stored in pgStatSnapshotHash.
+ */
+static void *
+snapshot_statentry(const PgStatTypes type, const Oid dbid, const Oid objid)
+{
+	PgStatSnapshot *snap = NULL;
+	bool		found;
+	PgStatHashEntryKey key;
+	size_t		statentsize = pgstat_entsize[type];
+
+	Assert(type != PGSTAT_TYPE_ALL);
+
+	/*
+	 * Create new hash, with rather arbitrary initial number of entries since
+	 * we don't know how this hash will grow.
+	 */
+	if (!pgStatSnapshotHash)
+	{
+		HASHCTL		ctl;
+
+		/*
+		 * Create the hash in the stats context
+		 *
+		 * The entry is prepended by common header part represented by
+		 * PgStatSnapshot.
+		 */
+
+		ctl.keysize = sizeof(PgStatHashEntryKey);
+		ctl.entrysize = PgStatSnapshotSize(statentsize);
+		ctl.hcxt = pgStatSnapshotContext;
+		pgStatSnapshotHash = hash_create("pgstat snapshot hash", 32, &ctl,
+										 HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+	}
+
+	/* Find a snapshot  */
+	key.type = type;
+	key.databaseid = dbid;
+	key.objectid = objid;
+
+	snap = hash_search(pgStatSnapshotHash, &key, HASH_ENTER, &found);
+
+	/*
+	 * Refer shared hash if not found in the snapshot hash.
+	 *
+	 * In transaction state, it is obvious that we should create a snapshot
+	 * entriy for consistency. If we are not, we return an up-to-date entry.
+	 * Having said that, we need a snapshot since shared stats entry can be
+	 * modified anytime. We share the same snapshot entry for the purpose.
+	 */
+	if (!found || !IsTransactionState())
+	{
+		PgStatEnvelope *shenv;
+
+		shenv = get_stat_entry(type, dbid, objid, true, NULL, NULL);
+
+		if (shenv)
+			memcpy(&snap->body, &shenv->body, statentsize);
+
+		snap->negative = !shenv;
+	}
+
+	if (snap->negative)
+		return NULL;
+
+	return &snap->body;
+}
+
+
 /* ----------
  * pgstat_fetch_stat_dbentry() -
  *
- *	Support function for the SQL-callable pgstat* functions. Returns
- *	the collected statistics for one database or NULL. NULL doesn't mean
- *	that the database doesn't exist, it is just not yet known by the
- *	collector, so the caller is better off to report ZERO instead.
+ *	Find database stats entry on backends. The returned entries are cached
+ *	until transaction end or pgstat_clear_snapshot() is called.
  * ----------
  */
 PgStat_StatDBEntry *
 pgstat_fetch_stat_dbentry(Oid dbid)
 {
-	/*
-	 * If not done for this transaction, read the statistics collector stats
-	 * file into some hash tables.
-	 */
-	backend_read_statsfile();
+	/* should be called from backends */
+	Assert(IsUnderPostmaster);
 
-	/*
-	 * Lookup the requested database; return NULL if not found
-	 */
-	return (PgStat_StatDBEntry *) hash_search(pgStatDBHash,
-											  (void *) &dbid,
-											  HASH_FIND, NULL);
+	/* If not done for this transaction, take a snapshot of global stats */
+	pgstat_snapshot_global_stats();
+
+	/* caller doesn't have a business with snapshot-local members */
+	return (PgStat_StatDBEntry *)
+		snapshot_statentry(PGSTAT_TYPE_DB, dbid, InvalidOid);
 }
 
-
 /* ----------
  * pgstat_fetch_stat_tabentry() -
  *
  *	Support function for the SQL-callable pgstat* functions. Returns
- *	the collected statistics for one table or NULL. NULL doesn't mean
+ *	the activity statistics for one table or NULL. NULL doesn't mean
  *	that the table doesn't exist, it is just not yet known by the
- *	collector, so the caller is better off to report ZERO instead.
+ *	activity statistics facilities, so the caller is better off to
+ *	report ZERO instead.
  * ----------
  */
 PgStat_StatTabEntry *
 pgstat_fetch_stat_tabentry(Oid relid)
 {
-	Oid			dbid;
-	PgStat_StatDBEntry *dbentry;
 	PgStat_StatTabEntry *tabentry;
 
-	/*
-	 * If not done for this transaction, read the statistics collector stats
-	 * file into some hash tables.
-	 */
-	backend_read_statsfile();
-
-	/*
-	 * Lookup our database, then look in its table hash table.
-	 */
-	dbid = MyDatabaseId;
-	dbentry = (PgStat_StatDBEntry *) hash_search(pgStatDBHash,
-												 (void *) &dbid,
-												 HASH_FIND, NULL);
-	if (dbentry != NULL && dbentry->tables != NULL)
-	{
-		tabentry = (PgStat_StatTabEntry *) hash_search(dbentry->tables,
-													   (void *) &relid,
-													   HASH_FIND, NULL);
-		if (tabentry)
-			return tabentry;
-	}
+	tabentry = pgstat_fetch_stat_tabentry_snapshot(false, relid);
+	if (tabentry != NULL)
+		return tabentry;
 
 	/*
 	 * If we didn't find it, maybe it's a shared table.
 	 */
-	dbid = InvalidOid;
-	dbentry = (PgStat_StatDBEntry *) hash_search(pgStatDBHash,
-												 (void *) &dbid,
-												 HASH_FIND, NULL);
-	if (dbentry != NULL && dbentry->tables != NULL)
-	{
-		tabentry = (PgStat_StatTabEntry *) hash_search(dbentry->tables,
-													   (void *) &relid,
-													   HASH_FIND, NULL);
-		if (tabentry)
-			return tabentry;
-	}
-
-	return NULL;
+	tabentry = pgstat_fetch_stat_tabentry_snapshot(true, relid);
+	return tabentry;
+}
+
+
+/* ----------
+ * pgstat_fetch_stat_tabentry_snapshot() -
+ *
+ *	Find table stats entry on backends in dbent. The returned entry is cached
+ *	until transaction end or pgstat_clear_snapshot() is called.
+ */
+PgStat_StatTabEntry *
+pgstat_fetch_stat_tabentry_snapshot(bool shared, Oid reloid)
+{
+	Oid			dboid = (shared ? InvalidOid : MyDatabaseId);
+
+	/* should be called from backends */
+	Assert(IsUnderPostmaster);
+
+	return (PgStat_StatTabEntry *)
+		snapshot_statentry(PGSTAT_TYPE_TABLE, dboid, reloid);
+}
+
+
+/* ----------
+ * pgstat_copy_index_counters() -
+ *
+ *	Support function for index swapping. Copy a portion of the counters of the
+ *	relation to specified place.
+ * ----------
+ */
+void
+pgstat_copy_index_counters(Oid relid, PgStat_TableStatus *dst)
+{
+	PgStat_StatTabEntry *tabentry;
+
+	/* No point fetching tabentry when dst is NULL */
+	if (!dst)
+		return;
+
+	tabentry = pgstat_fetch_stat_tabentry(relid);
+
+	if (!tabentry)
+		return;
+
+	dst->t_counts.t_numscans = tabentry->numscans;
+	dst->t_counts.t_tuples_returned = tabentry->tuples_returned;
+	dst->t_counts.t_tuples_fetched = tabentry->tuples_fetched;
+	dst->t_counts.t_blocks_fetched = tabentry->blocks_fetched;
+	dst->t_counts.t_blocks_hit = tabentry->blocks_hit;
 }

@@ -2510,24 +2829,48 @@ pgstat_fetch_stat_tabentry(Oid relid)
 PgStat_StatFuncEntry *
 pgstat_fetch_stat_funcentry(Oid func_id)
 {
-	PgStat_StatDBEntry *dbentry;
-	PgStat_StatFuncEntry *funcentry = NULL;
-
-	/* load the stats file if needed */
-	backend_read_statsfile();
-
-	/* Lookup our database, then find the requested function.  */
-	dbentry = pgstat_fetch_stat_dbentry(MyDatabaseId);
-	if (dbentry != NULL && dbentry->functions != NULL)
-	{
-		funcentry = (PgStat_StatFuncEntry *) hash_search(dbentry->functions,
-														 (void *) &func_id,
-														 HASH_FIND, NULL);
-	}
-
-	return funcentry;
+	/* should be called from backends */
+	Assert(IsUnderPostmaster);
+
+	return (PgStat_StatFuncEntry *)
+		snapshot_statentry(PGSTAT_TYPE_FUNCTION, MyDatabaseId, func_id);
 }
 
+/*
+ * pgstat_snapshot_global_stats() -
+ *
+ * Makes a snapshot of global stats if not done yet.  They will be kept until
+ * subsequent call of pgstat_clear_snapshot() or the end of the current
+ * memory context (typically TopTransactionContext).
+ * ----------
+ */
+static void
+pgstat_snapshot_global_stats(void)
+{
+	MemoryContext oldcontext;
+
+	attach_shared_stats();
+
+	/* Nothing to do if already done */
+	if (global_snapshot_is_valid)
+		return;
+
+	oldcontext = MemoryContextSwitchTo(pgStatSnapshotContext);
+
+	LWLockAcquire(StatsLock, LW_SHARED);
+	memcpy(&snapshot_globalStats, shared_globalStats,
+		   sizeof(PgStat_GlobalStats));
+
+	memcpy(&snapshot_archiverStats, shared_archiverStats,
+		   sizeof(PgStat_ArchiverStats));
+	LWLockRelease(StatsLock);
+
+	global_snapshot_is_valid = true;
+
+	MemoryContextSwitchTo(oldcontext);
+
+	return;
+}
 
 /* ----------
  * pgstat_fetch_stat_beentry() -
@@ -2599,9 +2942,10 @@ pgstat_fetch_stat_numbackends(void)
 PgStat_ArchiverStats *
 pgstat_fetch_stat_archiver(void)
 {
-	backend_read_statsfile();
+	/* If not done for this transaction, take a stats snapshot */
+	pgstat_snapshot_global_stats();
 
-	return &archiverStats;
+	return &snapshot_archiverStats;
 }

@@ -2616,9 +2960,10 @@ pgstat_fetch_stat_archiver(void)
 PgStat_GlobalStats *
 pgstat_fetch_global(void)
 {
-	backend_read_statsfile();
+	/* If not done for this transaction, take a stats snapshot */
+	pgstat_snapshot_global_stats();
 
-	return &globalStats;
+	return &snapshot_globalStats;
 }

@@ -2832,8 +3177,8 @@ pgstat_initialize(void)
 		MyBEEntry = &BackendStatusArray[MaxBackends + MyAuxProcType];
 	}
 
-	/* Set up a process-exit hook to clean up */
-	on_shmem_exit(pgstat_beshutdown_hook, 0);
+	/* need to be called before dsm shutdown */
+	before_shmem_exit(pgstat_beshutdown_hook, 0);
 }
 
 /* ----------
@@ -3009,12 +3354,15 @@ pgstat_bestart(void)
 	/* Update app name to current GUC setting */
 	if (application_name)
 		pgstat_report_appname(application_name);
+
+	/* attach shared database stats area */
+	attach_shared_stats();
 }
 
 /*
  * Shut down a single backend's statistics reporting at process exit.
  *
- * Flush any remaining statistics counts out to the collector.
+ * Flush any remaining statistics counts out to shared stats.
  * Without this, operations triggered during backend exit (such as
  * temp table deletions) won't be counted.
  *
@@ -3027,7 +3375,7 @@ pgstat_beshutdown_hook(int code, Datum arg)
 
 	/*
 	 * If we got as far as discovering our own database ID, we can report what
-	 * we did to the collector.  Otherwise, we'd be sending an invalid
+	 * we did to the shares stats.  Otherwise, we'd be sending an invalid
 	 * database ID, so forget it.  (This means that accesses to pg_database
 	 * during failed backend starts might never get counted.)
 	 */
@@ -3044,6 +3392,8 @@ pgstat_beshutdown_hook(int code, Datum arg)
 	beentry->st_procpid = 0;	/* mark invalid */
 
 	PGSTAT_END_WRITE_ACTIVITY(beentry);
+
+	detach_shared_stats(true);
 }

@@ -3304,7 +3654,8 @@ pgstat_read_current_status(void)
 #endif
 	int			i;
 
-	Assert(!pgStatRunningInCollector);
+	Assert(IsUnderPostmaster);
+
 	if (localBackendStatusTable)
 		return;					/* already done */
 
@@ -3599,9 +3950,6 @@ pgstat_get_wait_activity(WaitEventActivity w)
 		case WAIT_EVENT_LOGICAL_LAUNCHER_MAIN:
 			event_name = "LogicalLauncherMain";
 			break;
-		case WAIT_EVENT_PGSTAT_MAIN:
-			event_name = "PgStatMain";
-			break;
 		case WAIT_EVENT_RECOVERY_WAL_STREAM:
 			event_name = "RecoveryWalStream";
 			break;
@@ -4230,94 +4578,71 @@ pgstat_get_crashed_backend_activity(int pid, char *buffer, int buflen)

 /* ----------
- * pgstat_setheader() -
+ * pgstat_report_archiver() -
  *
- *		Set common header fields in a statistics message
- * ----------
- */
-static void
-pgstat_setheader(PgStat_MsgHdr *hdr, StatMsgType mtype)
-{
-	hdr->m_type = mtype;
-}
-
-
-/* ----------
- * pgstat_send() -
- *
- *		Send out one statistics message to the collector
- * ----------
- */
-static void
-pgstat_send(void *msg, int len)
-{
-	int			rc;
-
-	if (pgStatSock == PGINVALID_SOCKET)
-		return;
-
-	((PgStat_MsgHdr *) msg)->m_size = len;
-
-	/* We'll retry after EINTR, but ignore all other failures */
-	do
-	{
-		rc = send(pgStatSock, msg, len, 0);
-	} while (rc < 0 && errno == EINTR);
-
-#ifdef USE_ASSERT_CHECKING
-	/* In debug builds, log send failures ... */
-	if (rc < 0)
-		elog(LOG, "could not send to statistics collector: %m");
-#endif
-}
-
-/* ----------
- * pgstat_send_archiver() -
- *
- *	Tell the collector about the WAL file that we successfully
- *	archived or failed to archive.
+ *		Report archiver statistics
  * ----------
  */
 void
-pgstat_send_archiver(const char *xlog, bool failed)
+pgstat_report_archiver(const char *xlog, bool failed)
 {
-	PgStat_MsgArchiver msg;
+	TimestampTz now = GetCurrentTimestamp();
 
-	/*
-	 * Prepare and send the message
-	 */
-	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_ARCHIVER);
-	msg.m_failed = failed;
-	StrNCpy(msg.m_xlog, xlog, sizeof(msg.m_xlog));
-	msg.m_timestamp = GetCurrentTimestamp();
-	pgstat_send(&msg, sizeof(msg));
+	if (failed)
+	{
+		/* Failed archival attempt */
+		LWLockAcquire(StatsLock, LW_EXCLUSIVE);
+		++shared_archiverStats->failed_count;
+		memcpy(shared_archiverStats->last_failed_wal, xlog,
+			   sizeof(shared_archiverStats->last_failed_wal));
+		shared_archiverStats->last_failed_timestamp = now;
+		LWLockRelease(StatsLock);
+	}
+	else
+	{
+		/* Successful archival operation */
+		LWLockAcquire(StatsLock, LW_EXCLUSIVE);
+		++shared_archiverStats->archived_count;
+		memcpy(shared_archiverStats->last_archived_wal, xlog,
+			   sizeof(shared_archiverStats->last_archived_wal));
+		shared_archiverStats->last_archived_timestamp = now;
+		LWLockRelease(StatsLock);
+	}
 }
 
 /* ----------
- * pgstat_send_bgwriter() -
+ * pgstat_report_bgwriter() -
  *
- *		Send bgwriter statistics to the collector
+ *		Report bgwriter statistics
  * ----------
  */
 void
-pgstat_send_bgwriter(void)
+pgstat_report_bgwriter(void)
 {
 	/* We assume this initializes to zeroes */
-	static const PgStat_MsgBgWriter all_zeroes;
+	static const PgStat_BgWriter all_zeroes;
+
+	PgStat_BgWriter *l = &BgWriterStats;
 
 	/*
 	 * This function can be called even if nothing at all has happened. In
-	 * this case, avoid sending a completely empty message to the stats
-	 * collector.
+	 * this case, avoid taking lock for a completely empty stats.
 	 */
-	if (memcmp(&BgWriterStats, &all_zeroes, sizeof(PgStat_MsgBgWriter)) == 0)
+	if (memcmp(&BgWriterStats, &all_zeroes, sizeof(PgStat_BgWriter)) == 0)
 		return;
 
-	/*
-	 * Prepare and send the message
-	 */
-	pgstat_setheader(&BgWriterStats.m_hdr, PGSTAT_MTYPE_BGWRITER);
-	pgstat_send(&BgWriterStats, sizeof(BgWriterStats));
+	LWLockAcquire(StatsLock, LW_EXCLUSIVE);
+	shared_globalStats->timed_checkpoints += l->timed_checkpoints;
+	shared_globalStats->requested_checkpoints += l->requested_checkpoints;
+	shared_globalStats->checkpoint_write_time += l->checkpoint_write_time;
+	shared_globalStats->checkpoint_sync_time += l->checkpoint_sync_time;
+	shared_globalStats->buf_written_checkpoints += l->buf_written_checkpoints;
+	shared_globalStats->buf_written_clean += l->buf_written_clean;
+	shared_globalStats->maxwritten_clean += l->maxwritten_clean;
+	shared_globalStats->buf_written_backend += l->buf_written_backend;
+	shared_globalStats->buf_fsync_backend += l->buf_fsync_backend;
+	shared_globalStats->buf_alloc += l->buf_alloc;
+	LWLockRelease(StatsLock);
 
 	/*
 	 * Clear out the statistics buffer, so it can be re-used.
@@ -4326,425 +4651,30 @@ pgstat_send_bgwriter(void)
 }

-/* ----------
- * PgstatCollectorMain() -
- *
- *	Start up the statistics collector process.  This is the body of the
- *	postmaster child process.
- *
- *	The argc/argv parameters are valid only in EXEC_BACKEND case.
- * ----------
- */
-NON_EXEC_STATIC void
-PgstatCollectorMain(int argc, char *argv[])
-{
-	int			len;
-	PgStat_Msg	msg;
-	int			wr;
-
-	/*
-	 * Ignore all signals usually bound to some action in the postmaster,
-	 * except SIGHUP and SIGQUIT.  Note we don't need a SIGUSR1 handler to
-	 * support latch operations, because we only use a local latch.
-	 */
-	pqsignal(SIGHUP, SignalHandlerForConfigReload);
-	pqsignal(SIGINT, SIG_IGN);
-	pqsignal(SIGTERM, SIG_IGN);
-	pqsignal(SIGQUIT, SignalHandlerForShutdownRequest);
-	pqsignal(SIGALRM, SIG_IGN);
-	pqsignal(SIGPIPE, SIG_IGN);
-	pqsignal(SIGUSR1, SIG_IGN);
-	pqsignal(SIGUSR2, SIG_IGN);
-	/* Reset some signals that are accepted by postmaster but not here */
-	pqsignal(SIGCHLD, SIG_DFL);
-	PG_SETMASK(&UnBlockSig);
-
-	MyBackendType = B_STATS_COLLECTOR;
-	init_ps_display(NULL);
-
-	/*
-	 * Read in existing stats files or initialize the stats to zero.
-	 */
-	pgStatRunningInCollector = true;
-	pgStatDBHash = pgstat_read_statsfiles(InvalidOid, true, true);
-
-	/*
-	 * Loop to process messages until we get SIGQUIT or detect ungraceful
-	 * death of our parent postmaster.
-	 *
-	 * For performance reasons, we don't want to do ResetLatch/WaitLatch after
-	 * every message; instead, do that only after a recv() fails to obtain a
-	 * message.  (This effectively means that if backends are sending us stuff
-	 * like mad, we won't notice postmaster death until things slack off a
-	 * bit; which seems fine.)	To do that, we have an inner loop that
-	 * iterates as long as recv() succeeds.  We do check ConfigReloadPending
-	 * inside the inner loop, which means that such interrupts will get
-	 * serviced but the latch won't get cleared until next time there is a
-	 * break in the action.
-	 */
-	for (;;)
-	{
-		/* Clear any already-pending wakeups */
-		ResetLatch(MyLatch);
-
-		/*
-		 * Quit if we get SIGQUIT from the postmaster.
-		 */
-		if (ShutdownRequestPending)
-			break;
-
-		/*
-		 * Inner loop iterates as long as we keep getting messages, or until
-		 * ShutdownRequestPending becomes set.
-		 */
-		while (!ShutdownRequestPending)
-		{
-			/*
-			 * Reload configuration if we got SIGHUP from the postmaster.
-			 */
-			if (ConfigReloadPending)
-			{
-				ConfigReloadPending = false;
-				ProcessConfigFile(PGC_SIGHUP);
-			}
-
-			/*
-			 * Write the stats file(s) if a new request has arrived that is
-			 * not satisfied by existing file(s).
-			 */
-			if (pgstat_write_statsfile_needed())
-				pgstat_write_statsfiles(false, false);
-
-			/*
-			 * Try to receive and process a message.  This will not block,
-			 * since the socket is set to non-blocking mode.
-			 *
-			 * XXX On Windows, we have to force pgwin32_recv to cooperate,
-			 * despite the previous use of pg_set_noblock() on the socket.
-			 * This is extremely broken and should be fixed someday.
-			 */
-#ifdef WIN32
-			pgwin32_noblock = 1;
-#endif
-
-			len = recv(pgStatSock, (char *) &msg,
-					   sizeof(PgStat_Msg), 0);
-
-#ifdef WIN32
-			pgwin32_noblock = 0;
-#endif
-
-			if (len < 0)
-			{
-				if (errno == EAGAIN || errno == EWOULDBLOCK || errno == EINTR)
-					break;		/* out of inner loop */
-				ereport(ERROR,
-						(errcode_for_socket_access(),
-						 errmsg("could not read statistics message: %m")));
-			}
-
-			/*
-			 * We ignore messages that are smaller than our common header
-			 */
-			if (len < sizeof(PgStat_MsgHdr))
-				continue;
-
-			/*
-			 * The received length must match the length in the header
-			 */
-			if (msg.msg_hdr.m_size != len)
-				continue;
-
-			/*
-			 * O.K. - we accept this message.  Process it.
-			 */
-			switch (msg.msg_hdr.m_type)
-			{
-				case PGSTAT_MTYPE_DUMMY:
-					break;
-
-				case PGSTAT_MTYPE_INQUIRY:
-					pgstat_recv_inquiry(&msg.msg_inquiry, len);
-					break;
-
-				case PGSTAT_MTYPE_TABSTAT:
-					pgstat_recv_tabstat(&msg.msg_tabstat, len);
-					break;
-
-				case PGSTAT_MTYPE_TABPURGE:
-					pgstat_recv_tabpurge(&msg.msg_tabpurge, len);
-					break;
-
-				case PGSTAT_MTYPE_DROPDB:
-					pgstat_recv_dropdb(&msg.msg_dropdb, len);
-					break;
-
-				case PGSTAT_MTYPE_RESETCOUNTER:
-					pgstat_recv_resetcounter(&msg.msg_resetcounter, len);
-					break;
-
-				case PGSTAT_MTYPE_RESETSHAREDCOUNTER:
-					pgstat_recv_resetsharedcounter(&msg.msg_resetsharedcounter,
-												   len);
-					break;
-
-				case PGSTAT_MTYPE_RESETSINGLECOUNTER:
-					pgstat_recv_resetsinglecounter(&msg.msg_resetsinglecounter,
-												   len);
-					break;
-
-				case PGSTAT_MTYPE_AUTOVAC_START:
-					pgstat_recv_autovac(&msg.msg_autovacuum_start, len);
-					break;
-
-				case PGSTAT_MTYPE_VACUUM:
-					pgstat_recv_vacuum(&msg.msg_vacuum, len);
-					break;
-
-				case PGSTAT_MTYPE_ANALYZE:
-					pgstat_recv_analyze(&msg.msg_analyze, len);
-					break;
-
-				case PGSTAT_MTYPE_ARCHIVER:
-					pgstat_recv_archiver(&msg.msg_archiver, len);
-					break;
-
-				case PGSTAT_MTYPE_BGWRITER:
-					pgstat_recv_bgwriter(&msg.msg_bgwriter, len);
-					break;
-
-				case PGSTAT_MTYPE_FUNCSTAT:
-					pgstat_recv_funcstat(&msg.msg_funcstat, len);
-					break;
-
-				case PGSTAT_MTYPE_FUNCPURGE:
-					pgstat_recv_funcpurge(&msg.msg_funcpurge, len);
-					break;
-
-				case PGSTAT_MTYPE_RECOVERYCONFLICT:
-					pgstat_recv_recoveryconflict(&msg.msg_recoveryconflict,
-												 len);
-					break;
-
-				case PGSTAT_MTYPE_DEADLOCK:
-					pgstat_recv_deadlock(&msg.msg_deadlock, len);
-					break;
-
-				case PGSTAT_MTYPE_TEMPFILE:
-					pgstat_recv_tempfile(&msg.msg_tempfile, len);
-					break;
-
-				case PGSTAT_MTYPE_CHECKSUMFAILURE:
-					pgstat_recv_checksum_failure(&msg.msg_checksumfailure,
-												 len);
-					break;
-
-				default:
-					break;
-			}
-		}						/* end of inner message-processing loop */
-
-		/* Sleep until there's something to do */
-#ifndef WIN32
-		wr = WaitLatchOrSocket(MyLatch,
-							   WL_LATCH_SET | WL_POSTMASTER_DEATH | WL_SOCKET_READABLE,
-							   pgStatSock, -1L,
-							   WAIT_EVENT_PGSTAT_MAIN);
-#else
-
-		/*
-		 * Windows, at least in its Windows Server 2003 R2 incarnation,
-		 * sometimes loses FD_READ events.  Waking up and retrying the recv()
-		 * fixes that, so don't sleep indefinitely.  This is a crock of the
-		 * first water, but until somebody wants to debug exactly what's
-		 * happening there, this is the best we can do.  The two-second
-		 * timeout matches our pre-9.2 behavior, and needs to be short enough
-		 * to not provoke "using stale statistics" complaints from
-		 * backend_read_statsfile.
-		 */
-		wr = WaitLatchOrSocket(MyLatch,
-							   WL_LATCH_SET | WL_POSTMASTER_DEATH | WL_SOCKET_READABLE | WL_TIMEOUT,
-							   pgStatSock,
-							   2 * 1000L /* msec */ ,
-							   WAIT_EVENT_PGSTAT_MAIN);
-#endif
-
-		/*
-		 * Emergency bailout if postmaster has died.  This is to avoid the
-		 * necessity for manual cleanup of all postmaster children.
-		 */
-		if (wr & WL_POSTMASTER_DEATH)
-			break;
-	}							/* end of outer loop */
-
-	/*
-	 * Save the final stats to reuse at next startup.
-	 */
-	pgstat_write_statsfiles(true, true);
-
-	exit(0);
-}
-
-/*
- * Subroutine to clear stats in a database entry
- *
- * Tables and functions hashes are initialized to empty.
- */
-static void
-reset_dbentry_counters(PgStat_StatDBEntry *dbentry)
-{
-	HASHCTL		hash_ctl;
-
-	dbentry->n_xact_commit = 0;
-	dbentry->n_xact_rollback = 0;
-	dbentry->n_blocks_fetched = 0;
-	dbentry->n_blocks_hit = 0;
-	dbentry->n_tuples_returned = 0;
-	dbentry->n_tuples_fetched = 0;
-	dbentry->n_tuples_inserted = 0;
-	dbentry->n_tuples_updated = 0;
-	dbentry->n_tuples_deleted = 0;
-	dbentry->last_autovac_time = 0;
-	dbentry->n_conflict_tablespace = 0;
-	dbentry->n_conflict_lock = 0;
-	dbentry->n_conflict_snapshot = 0;
-	dbentry->n_conflict_bufferpin = 0;
-	dbentry->n_conflict_startup_deadlock = 0;
-	dbentry->n_temp_files = 0;
-	dbentry->n_temp_bytes = 0;
-	dbentry->n_deadlocks = 0;
-	dbentry->n_checksum_failures = 0;
-	dbentry->last_checksum_failure = 0;
-	dbentry->n_block_read_time = 0;
-	dbentry->n_block_write_time = 0;
-
-	dbentry->stat_reset_timestamp = GetCurrentTimestamp();
-	dbentry->stats_timestamp = 0;
-
-	memset(&hash_ctl, 0, sizeof(hash_ctl));
-	hash_ctl.keysize = sizeof(Oid);
-	hash_ctl.entrysize = sizeof(PgStat_StatTabEntry);
-	dbentry->tables = hash_create("Per-database table",
-								  PGSTAT_TAB_HASH_SIZE,
-								  &hash_ctl,
-								  HASH_ELEM | HASH_BLOBS);
-
-	hash_ctl.keysize = sizeof(Oid);
-	hash_ctl.entrysize = sizeof(PgStat_StatFuncEntry);
-	dbentry->functions = hash_create("Per-database function",
-									 PGSTAT_FUNCTION_HASH_SIZE,
-									 &hash_ctl,
-									 HASH_ELEM | HASH_BLOBS);
-}
-
-/*
- * Lookup the hash table entry for the specified database. If no hash
- * table entry exists, initialize it, if the create parameter is true.
- * Else, return NULL.
- */
-static PgStat_StatDBEntry *
-pgstat_get_db_entry(Oid databaseid, bool create)
-{
-	PgStat_StatDBEntry *result;
-	bool		found;
-	HASHACTION	action = (create ? HASH_ENTER : HASH_FIND);
-
-	/* Lookup or create the hash table entry for this database */
-	result = (PgStat_StatDBEntry *) hash_search(pgStatDBHash,
-												&databaseid,
-												action, &found);
-
-	if (!create && !found)
-		return NULL;
-
-	/*
-	 * If not found, initialize the new one.  This creates empty hash tables
-	 * for tables and functions, too.
-	 */
-	if (!found)
-		reset_dbentry_counters(result);
-
-	return result;
-}
-
-
-/*
- * Lookup the hash table entry for the specified table. If no hash
- * table entry exists, initialize it, if the create parameter is true.
- * Else, return NULL.
- */
-static PgStat_StatTabEntry *
-pgstat_get_tab_entry(PgStat_StatDBEntry *dbentry, Oid tableoid, bool create)
-{
-	PgStat_StatTabEntry *result;
-	bool		found;
-	HASHACTION	action = (create ? HASH_ENTER : HASH_FIND);
-
-	/* Lookup or create the hash table entry for this table */
-	result = (PgStat_StatTabEntry *) hash_search(dbentry->tables,
-												 &tableoid,
-												 action, &found);
-
-	if (!create && !found)
-		return NULL;
-
-	/* If not found, initialize the new one. */
-	if (!found)
-	{
-		result->numscans = 0;
-		result->tuples_returned = 0;
-		result->tuples_fetched = 0;
-		result->tuples_inserted = 0;
-		result->tuples_updated = 0;
-		result->tuples_deleted = 0;
-		result->tuples_hot_updated = 0;
-		result->n_live_tuples = 0;
-		result->n_dead_tuples = 0;
-		result->changes_since_analyze = 0;
-		result->inserts_since_vacuum = 0;
-		result->blocks_fetched = 0;
-		result->blocks_hit = 0;
-		result->vacuum_timestamp = 0;
-		result->vacuum_count = 0;
-		result->autovac_vacuum_timestamp = 0;
-		result->autovac_vacuum_count = 0;
-		result->analyze_timestamp = 0;
-		result->analyze_count = 0;
-		result->autovac_analyze_timestamp = 0;
-		result->autovac_analyze_count = 0;
-	}
-
-	return result;
-}
-
-
 /* ----------
  * pgstat_write_statsfiles() -
- *		Write the global statistics file, as well as requested DB files.
- *
- *	'permanent' specifies writing to the permanent files not temporary ones.
- *	When true (happens only when the collector is shutting down), also remove
- *	the temporary files so that backends starting up under a new postmaster
- *	can't read old data before the new collector is ready.
- *
- *	When 'allDbs' is false, only the requested databases (listed in
- *	pending_write_requests) will be written; otherwise, all databases
- *	will be written.
+ *		Write the global statistics file, as well as DB files.
  * ----------
  */
-static void
-pgstat_write_statsfiles(bool permanent, bool allDbs)
+void
+pgstat_write_statsfiles(void)
 {
-	HASH_SEQ_STATUS hstat;
-	PgStat_StatDBEntry *dbentry;
 	FILE	   *fpout;
 	int32		format_id;
-	const char *tmpfile = permanent ? PGSTAT_STAT_PERMANENT_TMPFILE : pgstat_stat_tmpname;
-	const char *statfile = permanent ? PGSTAT_STAT_PERMANENT_FILENAME : pgstat_stat_filename;
+	const char *tmpfile = PGSTAT_STAT_PERMANENT_TMPFILE;
+	const char *statfile = PGSTAT_STAT_PERMANENT_FILENAME;
 	int			rc;
+	PgStatEnvelope **envlist;
+	PgStatEnvelope **penv;
+
+	/* stats is not initialized yet. just return. */
+	if (StatsShmem->stats_dsa_handle == DSM_HANDLE_INVALID)
+		return;
 
 	elog(DEBUG2, "writing stats file \"%s\"", statfile);
 
+	create_missing_dbentries();
+
 	/*
 	 * Open the statistics temp file to write out the current values.
 	 */
@@ -4761,7 +4691,7 @@ pgstat_write_statsfiles(bool permanent, bool allDbs)
 	/*
 	 * Set the timestamp of the stats file.
 	 */
-	globalStats.stats_timestamp = GetCurrentTimestamp();
+	shared_globalStats->stats_timestamp = GetCurrentTimestamp();
 
 	/*
 	 * Write the file header --- currently just a format ID.
@@ -4773,32 +4703,31 @@ pgstat_write_statsfiles(bool permanent, bool allDbs)
 	/*
 	 * Write global stats struct
 	 */
-	rc = fwrite(&globalStats, sizeof(globalStats), 1, fpout);
+	rc = fwrite(shared_globalStats, sizeof(*shared_globalStats), 1, fpout);
 	(void) rc;					/* we'll check for error with ferror */
 
 	/*
 	 * Write archiver stats struct
 	 */
-	rc = fwrite(&archiverStats, sizeof(archiverStats), 1, fpout);
+	rc = fwrite(shared_archiverStats, sizeof(*shared_archiverStats), 1, fpout);
 	(void) rc;					/* we'll check for error with ferror */
 
 	/*
 	 * Walk through the database table.
 	 */
-	hash_seq_init(&hstat, pgStatDBHash);
-	while ((dbentry = (PgStat_StatDBEntry *) hash_seq_search(&hstat)) != NULL)
+	envlist = collect_stat_entries(PGSTAT_TYPE_DB, InvalidOid);
+	for (penv = envlist; *penv != NULL; penv++)
 	{
+		PgStat_StatDBEntry *dbentry = (PgStat_StatDBEntry *) &(*penv)->body;
+
 		/*
 		 * Write out the table and function stats for this DB into the
 		 * appropriate per-DB stat file, if required.
 		 */
-		if (allDbs || pgstat_db_requested(dbentry->databaseid))
-		{
-			/* Make DB's timestamp consistent with the global stats */
-			dbentry->stats_timestamp = globalStats.stats_timestamp;
+		/* Make DB's timestamp consistent with the global stats */
+		dbentry->stats_timestamp = shared_globalStats->stats_timestamp;
 
-			pgstat_write_db_statsfile(dbentry, permanent);
-		}
+		pgstat_write_database_stats(dbentry);
 
 		/*
 		 * Write out the DB entry. We don't write the tables or functions
@@ -4809,6 +4738,8 @@ pgstat_write_statsfiles(bool permanent, bool allDbs)
 		(void) rc;				/* we'll check for error with ferror */
 	}
 
+	pfree(envlist);
+
 	/*
 	 * No more output to be done. Close the temp file and replace the old
 	 * pgstat.stat with it.  The ferror() check replaces testing for error
@@ -4841,55 +4772,19 @@ pgstat_write_statsfiles(bool permanent, bool allDbs)
 						tmpfile, statfile)));
 		unlink(tmpfile);
 	}
-
-	if (permanent)
-		unlink(pgstat_stat_filename);
-
-	/*
-	 * Now throw away the list of requests.  Note that requests sent after we
-	 * started the write are still waiting on the network socket.
-	 */
-	list_free(pending_write_requests);
-	pending_write_requests = NIL;
 }
 
-/*
- * return the filename for a DB stat file; filename is the output buffer,
- * of length len.
- */
-static void
-get_dbstat_filename(bool permanent, bool tempname, Oid databaseid,
-					char *filename, int len)
-{
-	int			printed;
-
-	/* NB -- pgstat_reset_remove_files knows about the pattern this uses */
-	printed = snprintf(filename, len, "%s/db_%u.%s",
-					   permanent ? PGSTAT_STAT_PERMANENT_DIRECTORY :
-					   pgstat_stat_directory,
-					   databaseid,
-					   tempname ? "tmp" : "stat");
-	if (printed >= len)
-		elog(ERROR, "overlength pgstat path");
-}
 
 /* ----------
- * pgstat_write_db_statsfile() -
- *		Write the stat file for a single database.
- *
- *	If writing to the permanent file (happens when the collector is
- *	shutting down only), remove the temporary file so that backends
- *	starting up under a new postmaster can't read the old data before
- *	the new collector is ready.
+ * pgstat_write_database_stats() -
+ *  Write the stat file for a single database.
  * ----------
  */
 static void
-pgstat_write_db_statsfile(PgStat_StatDBEntry *dbentry, bool permanent)
+pgstat_write_database_stats(PgStat_StatDBEntry *dbentry)
 {
-	HASH_SEQ_STATUS tstat;
-	HASH_SEQ_STATUS fstat;
-	PgStat_StatTabEntry *tabentry;
-	PgStat_StatFuncEntry *funcentry;
+	PgStatEnvelope **envlist;
+	PgStatEnvelope **penv;
 	FILE	   *fpout;
 	int32		format_id;
 	Oid			dbid = dbentry->databaseid;
@@ -4897,8 +4792,8 @@ pgstat_write_db_statsfile(PgStat_StatDBEntry *dbentry, bool permanent)
 	char		tmpfile[MAXPGPATH];
 	char		statfile[MAXPGPATH];
 
-	get_dbstat_filename(permanent, true, dbid, tmpfile, MAXPGPATH);
-	get_dbstat_filename(permanent, false, dbid, statfile, MAXPGPATH);
+	get_dbstat_filename(true, dbid, tmpfile, MAXPGPATH);
+	get_dbstat_filename(false, dbid, statfile, MAXPGPATH);
 
 	elog(DEBUG2, "writing stats file \"%s\"", statfile);
 
@@ -4925,24 +4820,31 @@ pgstat_write_db_statsfile(PgStat_StatDBEntry *dbentry, bool permanent)
 	/*
 	 * Walk through the database's access stats per table.
 	 */
-	hash_seq_init(&tstat, dbentry->tables);
-	while ((tabentry = (PgStat_StatTabEntry *) hash_seq_search(&tstat)) != NULL)
+	envlist = collect_stat_entries(PGSTAT_TYPE_TABLE, dbentry->databaseid);
+	for (penv = envlist; *penv != NULL; penv++)
 	{
+		PgStat_StatTabEntry *tabentry = (PgStat_StatTabEntry *) &(*penv)->body;
+
 		fputc('T', fpout);
 		rc = fwrite(tabentry, sizeof(PgStat_StatTabEntry), 1, fpout);
 		(void) rc;				/* we'll check for error with ferror */
 	}
+	pfree(envlist);
 
 	/*
 	 * Walk through the database's function stats table.
 	 */
-	hash_seq_init(&fstat, dbentry->functions);
-	while ((funcentry = (PgStat_StatFuncEntry *) hash_seq_search(&fstat)) != NULL)
+	envlist = collect_stat_entries(PGSTAT_TYPE_FUNCTION, dbentry->databaseid);
+	for (penv = envlist; *penv != NULL; penv++)
 	{
+		PgStat_StatFuncEntry *funcentry =
+		(PgStat_StatFuncEntry *) &(*penv)->body;
+
 		fputc('F', fpout);
 		rc = fwrite(funcentry, sizeof(PgStat_StatFuncEntry), 1, fpout);
 		(void) rc;				/* we'll check for error with ferror */
 	}
+	pfree(envlist);
 
 	/*
 	 * No more output to be done. Close the temp file and replace the old
@@ -4976,94 +4878,165 @@ pgstat_write_db_statsfile(PgStat_StatDBEntry *dbentry, bool permanent)
 						tmpfile, statfile)));
 		unlink(tmpfile);
 	}
+}
 
-	if (permanent)
+/* ----------
+ * create_missing_dbentries() -
+ *
+ *  There may be the case where database entry is missing for the database
+ *  where object stats are recorded. This function creates such missing
+ *  dbentries so that so that all stats entries can be written out to files.
+ * ----------
+ */
+static void
+create_missing_dbentries(void)
+{
+	dshash_seq_status hstat;
+	PgStatHashEntry *p;
+	HTAB	   *oidhash;
+	HASHCTL		ctl;
+	HASH_SEQ_STATUS scan;
+	Oid		   *poid;
+
+	memset(&ctl, 0, sizeof(ctl));
+	ctl.keysize = sizeof(Oid);
+	ctl.entrysize = sizeof(Oid);
+	ctl.hcxt = CurrentMemoryContext;
+	oidhash = hash_create("Temporary table of OIDs",
+						  PGSTAT_TABLE_HASH_SIZE,
+						  &ctl,
+						  HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+
+	/* Collect OID from the shared stats hash */
+	dshash_seq_init(&hstat, pgStatSharedHash, false);
+	while ((p = dshash_seq_next(&hstat)) != NULL)
+		hash_search(oidhash, &p->key.databaseid, HASH_ENTER, NULL);
+	dshash_seq_term(&hstat);
+
+	/* Create missing database entries if not exists. */
+	hash_seq_init(&scan, oidhash);
+	while ((poid = (Oid *) hash_seq_search(&scan)) != NULL)
+		(void) get_stat_entry(PGSTAT_TYPE_DB, *poid, InvalidOid,
+							  false, init_dbentry, NULL);
+
+	hash_destroy(oidhash);
+}
+
+
+/* ----------
+ * get_stat_entry() -
+ *
+ *	get shared stats entry for specified type, dbid and objid.
+ *  If nowait is true, returns NULL on lock failure.
+ *
+ *  If initfunc is not NULL, new entry is created if not yet and the function
+ *  is called with the new envelope. If found is not NULL, it is set to true if
+ *  existing entry is found or false if not.
+ * ----------
+ */
+static PgStatEnvelope *
+get_stat_entry(PgStatTypes type, Oid dbid, Oid objid,
+			   bool nowait, entry_initializer initfunc, bool *found)
+{
+	bool		create = (initfunc != NULL);
+	PgStatHashEntry *shent;
+	PgStatEnvelope *shenv = NULL;
+	PgStatHashEntryKey key;
+	bool		myfound;
+
+	Assert(type != PGSTAT_TYPE_ALL);
+
+	key.type = type;
+	key.databaseid = dbid;
+	key.objectid = objid;
+	shent = dshash_find_extended(pgStatSharedHash, &key,
+								 create, nowait, create, &myfound);
+	if (shent)
 	{
-		get_dbstat_filename(false, false, dbid, statfile, MAXPGPATH);
+		if (create && !myfound)
+		{
+			/* Create new stats envelope. */
+			size_t		envsize = PgStatEnvelopeSize(pgstat_entsize[type]);
+			dsa_pointer chunk = dsa_allocate0(area, envsize);
 
-		elog(DEBUG2, "removing temporary stats file \"%s\"", statfile);
-		unlink(statfile);
+			shenv = dsa_get_address(area, chunk);
+			shenv->type = type;
+			shenv->databaseid = dbid;
+			shenv->objectid = objid;
+			shenv->len = pgstat_entsize[type];
+			LWLockInitialize(&shenv->lock, LWTRANCHE_STATS);
+
+			/*
+			 * The lock on dshsh is released just after. Call initializer
+			 * callback before it is exposed to other process.
+			 */
+			if (initfunc)
+				initfunc(shenv);
+
+			/* Link the new entry from the hash entry. */
+			shent->env = chunk;
+		}
+		else
+			shenv = dsa_get_address(area, shent->env);
+
+		dshash_release_lock(pgStatSharedHash, shent);
 	}
+
+	if (found)
+		*found = myfound;
+
+	return shenv;
 }
 
+
 /* ----------
  * pgstat_read_statsfiles() -
  *
- *	Reads in some existing statistics collector files and returns the
- *	databases hash table that is the top level of the data.
+ *	Reads in existing activity statistics files into the shared stats hash.
  *
- *	If 'onlydb' is not InvalidOid, it means we only want data for that DB
- *	plus the shared catalogs ("DB 0").  We'll still populate the DB hash
- *	table for all databases, but we don't bother even creating table/function
- *	hash tables for other databases.
- *
- *	'permanent' specifies reading from the permanent files not temporary ones.
- *	When true (happens only when the collector is starting up), remove the
- *	files after reading; the in-memory status is now authoritative, and the
- *	files would be out of date in case somebody else reads them.
- *
- *	If a 'deep' read is requested, table/function stats are read, otherwise
- *	the table/function hash tables remain empty.
  * ----------
  */
-static HTAB *
-pgstat_read_statsfiles(Oid onlydb, bool permanent, bool deep)
+void
+pgstat_read_statsfiles(void)
 {
+	PgStatEnvelope *env;
 	PgStat_StatDBEntry *dbentry;
 	PgStat_StatDBEntry dbbuf;
-	HASHCTL		hash_ctl;
-	HTAB	   *dbhash;
 	FILE	   *fpin;
 	int32		format_id;
 	bool		found;
-	const char *statfile = permanent ? PGSTAT_STAT_PERMANENT_FILENAME : pgstat_stat_filename;
+	const char *statfile = PGSTAT_STAT_PERMANENT_FILENAME;
 
-	/*
-	 * The tables will live in pgStatLocalContext.
-	 */
-	pgstat_setup_memcxt();
+	/* shouldn't be called from postmaster */
+	Assert(IsUnderPostmaster);
 
-	/*
-	 * Create the DB hashtable
-	 */
-	memset(&hash_ctl, 0, sizeof(hash_ctl));
-	hash_ctl.keysize = sizeof(Oid);
-	hash_ctl.entrysize = sizeof(PgStat_StatDBEntry);
-	hash_ctl.hcxt = pgStatLocalContext;
-	dbhash = hash_create("Databases hash", PGSTAT_DB_HASH_SIZE, &hash_ctl,
-						 HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
-
-	/*
-	 * Clear out global and archiver statistics so they start from zero in
-	 * case we can't load an existing statsfile.
-	 */
-	memset(&globalStats, 0, sizeof(globalStats));
-	memset(&archiverStats, 0, sizeof(archiverStats));
+	elog(DEBUG2, "reading stats file \"%s\"", statfile);
 
 	/*
 	 * Set the current timestamp (will be kept only in case we can't load an
 	 * existing statsfile).
 	 */
-	globalStats.stat_reset_timestamp = GetCurrentTimestamp();
-	archiverStats.stat_reset_timestamp = globalStats.stat_reset_timestamp;
+	shared_globalStats->stat_reset_timestamp = GetCurrentTimestamp();
+	shared_archiverStats->stat_reset_timestamp =
+		shared_globalStats->stat_reset_timestamp;
 
 	/*
 	 * Try to open the stats file. If it doesn't exist, the backends simply
-	 * return zero for anything and the collector simply starts from scratch
-	 * with empty counters.
+	 * returns zero for anything and the activity statistics simply starts
+	 * from scratch with empty counters.
 	 *
-	 * ENOENT is a possibility if the stats collector is not running or has
-	 * not yet written the stats file the first time.  Any other failure
+	 * ENOENT is a possibility if the activity statistics is not running or
+	 * has not yet written the stats file the first time.  Any other failure
 	 * condition is suspicious.
 	 */
 	if ((fpin = AllocateFile(statfile, PG_BINARY_R)) == NULL)
 	{
 		if (errno != ENOENT)
-			ereport(pgStatRunningInCollector ? LOG : WARNING,
+			ereport(LOG,
 					(errcode_for_file_access(),
 					 errmsg("could not open statistics file \"%s\": %m",
 							statfile)));
-		return dbhash;
+		return;
 	}
 
 	/*
@@ -5072,7 +5045,7 @@ pgstat_read_statsfiles(Oid onlydb, bool permanent, bool deep)
 	if (fread(&format_id, 1, sizeof(format_id), fpin) != sizeof(format_id) ||
 		format_id != PGSTAT_FILE_FORMAT_ID)
 	{
-		ereport(pgStatRunningInCollector ? LOG : WARNING,
+		ereport(LOG,
 				(errmsg("corrupted statistics file \"%s\"", statfile)));
 		goto done;
 	}
@@ -5080,38 +5053,30 @@ pgstat_read_statsfiles(Oid onlydb, bool permanent, bool deep)
 	/*
 	 * Read global stats struct
 	 */
-	if (fread(&globalStats, 1, sizeof(globalStats), fpin) != sizeof(globalStats))
+	if (fread(shared_globalStats, 1, sizeof(*shared_globalStats), fpin) !=
+		sizeof(*shared_globalStats))
 	{
-		ereport(pgStatRunningInCollector ? LOG : WARNING,
+		ereport(LOG,
 				(errmsg("corrupted statistics file \"%s\"", statfile)));
-		memset(&globalStats, 0, sizeof(globalStats));
+		MemSet(shared_globalStats, 0, sizeof(*shared_globalStats));
 		goto done;
 	}
 
-	/*
-	 * In the collector, disregard the timestamp we read from the permanent
-	 * stats file; we should be willing to write a temp stats file immediately
-	 * upon the first request from any backend.  This only matters if the old
-	 * file's timestamp is less than PGSTAT_STAT_INTERVAL ago, but that's not
-	 * an unusual scenario.
-	 */
-	if (pgStatRunningInCollector)
-		globalStats.stats_timestamp = 0;
-
 	/*
 	 * Read archiver stats struct
 	 */
-	if (fread(&archiverStats, 1, sizeof(archiverStats), fpin) != sizeof(archiverStats))
+	if (fread(shared_archiverStats, 1, sizeof(*shared_archiverStats), fpin) !=
+		sizeof(*shared_archiverStats))
 	{
-		ereport(pgStatRunningInCollector ? LOG : WARNING,
+		ereport(LOG,
 				(errmsg("corrupted statistics file \"%s\"", statfile)));
-		memset(&archiverStats, 0, sizeof(archiverStats));
+		MemSet(shared_archiverStats, 0, sizeof(*shared_archiverStats));
 		goto done;
 	}
 
 	/*
-	 * We found an existing collector stats file. Read it and put all the
-	 * hashtable entries into place.
+	 * We found an existing activity statistics file. Read it and put all the
+	 * hash table entries into place.
 	 */
 	for (;;)
 	{
@@ -5125,7 +5090,7 @@ pgstat_read_statsfiles(Oid onlydb, bool permanent, bool deep)
 				if (fread(&dbbuf, 1, offsetof(PgStat_StatDBEntry, tables),
 						  fpin) != offsetof(PgStat_StatDBEntry, tables))
 				{
-					ereport(pgStatRunningInCollector ? LOG : WARNING,
+					ereport(LOG,
 							(errmsg("corrupted statistics file \"%s\"",
 									statfile)));
 					goto done;
@@ -5134,76 +5099,33 @@ pgstat_read_statsfiles(Oid onlydb, bool permanent, bool deep)
 				/*
 				 * Add to the DB hash
 				 */
-				dbentry = (PgStat_StatDBEntry *) hash_search(dbhash,
-															 (void *) &dbbuf.databaseid,
-															 HASH_ENTER,
-															 &found);
+
+				env = get_stat_entry(PGSTAT_TYPE_DB, dbbuf.databaseid,
+									 InvalidOid,
+									 false, init_dbentry, &found);
+				dbentry = (PgStat_StatDBEntry *) &env->body;
+
+				/* don't allow duplicate dbentries */
 				if (found)
 				{
-					ereport(pgStatRunningInCollector ? LOG : WARNING,
+					ereport(LOG,
 							(errmsg("corrupted statistics file \"%s\"",
 									statfile)));
 					goto done;
 				}
 
-				memcpy(dbentry, &dbbuf, sizeof(PgStat_StatDBEntry));
-				dbentry->tables = NULL;
-				dbentry->functions = NULL;
-
-				/*
-				 * In the collector, disregard the timestamp we read from the
-				 * permanent stats file; we should be willing to write a temp
-				 * stats file immediately upon the first request from any
-				 * backend.
-				 */
-				if (pgStatRunningInCollector)
-					dbentry->stats_timestamp = 0;
-
-				/*
-				 * Don't create tables/functions hashtables for uninteresting
-				 * databases.
-				 */
-				if (onlydb != InvalidOid)
-				{
-					if (dbbuf.databaseid != onlydb &&
-						dbbuf.databaseid != InvalidOid)
-						break;
-				}
-
-				memset(&hash_ctl, 0, sizeof(hash_ctl));
-				hash_ctl.keysize = sizeof(Oid);
-				hash_ctl.entrysize = sizeof(PgStat_StatTabEntry);
-				hash_ctl.hcxt = pgStatLocalContext;
-				dbentry->tables = hash_create("Per-database table",
-											  PGSTAT_TAB_HASH_SIZE,
-											  &hash_ctl,
-											  HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
-
-				hash_ctl.keysize = sizeof(Oid);
-				hash_ctl.entrysize = sizeof(PgStat_StatFuncEntry);
-				hash_ctl.hcxt = pgStatLocalContext;
-				dbentry->functions = hash_create("Per-database function",
-												 PGSTAT_FUNCTION_HASH_SIZE,
-												 &hash_ctl,
-												 HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
-
-				/*
-				 * If requested, read the data from the database-specific
-				 * file.  Otherwise we just leave the hashtables empty.
-				 */
-				if (deep)
-					pgstat_read_db_statsfile(dbentry->databaseid,
-											 dbentry->tables,
-											 dbentry->functions,
-											 permanent);
+				memcpy(dbentry, &dbbuf,
+					   offsetof(PgStat_StatDBEntry, tables));
 
+				/* Read the data from the database-specific file. */
+				pgstat_read_db_statsfile(dbentry);
 				break;
 
 			case 'E':
 				goto done;
 
 			default:
-				ereport(pgStatRunningInCollector ? LOG : WARNING,
+				ereport(LOG,
 						(errmsg("corrupted statistics file \"%s\"",
 								statfile)));
 				goto done;
@@ -5213,59 +5135,50 @@ pgstat_read_statsfiles(Oid onlydb, bool permanent, bool deep)
 done:
 	FreeFile(fpin);
 
-	/* If requested to read the permanent file, also get rid of it. */
-	if (permanent)
-	{
-		elog(DEBUG2, "removing permanent stats file \"%s\"", statfile);
-		unlink(statfile);
-	}
+	elog(DEBUG2, "removing permanent stats file \"%s\"", statfile);
+	unlink(statfile);
 
-	return dbhash;
+	return;
 }

 /* ----------
  * pgstat_read_db_statsfile() -
  *
- *	Reads in the existing statistics collector file for the given database,
- *	filling the passed-in tables and functions hash tables.
- *
- *	As in pgstat_read_statsfiles, if the permanent file is requested, it is
- *	removed after reading.
- *
- *	Note: this code has the ability to skip storing per-table or per-function
- *	data, if NULL is passed for the corresponding hashtable.  That's not used
- *	at the moment though.
+ *	Reads in the at-rest statistics file and create shared statistics
+ *	tables. The file is removed after reading.
  * ----------
  */
 static void
-pgstat_read_db_statsfile(Oid databaseid, HTAB *tabhash, HTAB *funchash,
-						 bool permanent)
+pgstat_read_db_statsfile(PgStat_StatDBEntry *dbentry)
 {
+	PgStatEnvelope *env;
 	PgStat_StatTabEntry *tabentry;
 	PgStat_StatTabEntry tabbuf;
 	PgStat_StatFuncEntry funcbuf;
 	PgStat_StatFuncEntry *funcentry;
+	dshash_table *tabhash = NULL;
+	dshash_table *funchash = NULL;
 	FILE	   *fpin;
 	int32		format_id;
 	bool		found;
 	char		statfile[MAXPGPATH];
 
-	get_dbstat_filename(permanent, false, databaseid, statfile, MAXPGPATH);
+	get_dbstat_filename(false, dbentry->databaseid, statfile, MAXPGPATH);
 
 	/*
 	 * Try to open the stats file. If it doesn't exist, the backends simply
-	 * return zero for anything and the collector simply starts from scratch
-	 * with empty counters.
+	 * returns zero for anything and the activity statistics simply starts
+	 * from scratch with empty counters.
 	 *
-	 * ENOENT is a possibility if the stats collector is not running or has
-	 * not yet written the stats file the first time.  Any other failure
+	 * ENOENT is a possibility if the activity statistics is not running or
+	 * has not yet written the stats file the first time.  Any other failure
 	 * condition is suspicious.
 	 */
 	if ((fpin = AllocateFile(statfile, PG_BINARY_R)) == NULL)
 	{
 		if (errno != ENOENT)
-			ereport(pgStatRunningInCollector ? LOG : WARNING,
+			ereport(LOG,
 					(errcode_for_file_access(),
 					 errmsg("could not open statistics file \"%s\": %m",
 							statfile)));
@@ -5278,14 +5191,14 @@ pgstat_read_db_statsfile(Oid databaseid, HTAB *tabhash, HTAB *funchash,
 	if (fread(&format_id, 1, sizeof(format_id), fpin) != sizeof(format_id) ||
 		format_id != PGSTAT_FILE_FORMAT_ID)
 	{
-		ereport(pgStatRunningInCollector ? LOG : WARNING,
+		ereport(LOG,
 				(errmsg("corrupted statistics file \"%s\"", statfile)));
 		goto done;
 	}
 
 	/*
-	 * We found an existing collector stats file. Read it and put all the
-	 * hashtable entries into place.
+	 * We found an existing activity statistics file. Read it and put all the
+	 * hash table entries into place.
 	 */
 	for (;;)
 	{
@@ -5298,25 +5211,21 @@ pgstat_read_db_statsfile(Oid databaseid, HTAB *tabhash, HTAB *funchash,
 				if (fread(&tabbuf, 1, sizeof(PgStat_StatTabEntry),
 						  fpin) != sizeof(PgStat_StatTabEntry))
 				{
-					ereport(pgStatRunningInCollector ? LOG : WARNING,
+					ereport(LOG,
 							(errmsg("corrupted statistics file \"%s\"",
 									statfile)));
 					goto done;
 				}
 
-				/*
-				 * Skip if table data not wanted.
-				 */
-				if (tabhash == NULL)
-					break;
-
-				tabentry = (PgStat_StatTabEntry *) hash_search(tabhash,
-															   (void *) &tabbuf.tableid,
-															   HASH_ENTER, &found);
+				env = get_stat_entry(PGSTAT_TYPE_TABLE,
+									 dbentry->databaseid, tabbuf.tableid,
+									 false, init_tabentry, &found);
+				tabentry = (PgStat_StatTabEntry *) &env->body;
 
+				/* don't allow duplicate entries */
 				if (found)
 				{
-					ereport(pgStatRunningInCollector ? LOG : WARNING,
+					ereport(LOG,
 							(errmsg("corrupted statistics file \"%s\"",
 									statfile)));
 					goto done;
@@ -5332,25 +5241,20 @@ pgstat_read_db_statsfile(Oid databaseid, HTAB *tabhash, HTAB *funchash,
 				if (fread(&funcbuf, 1, sizeof(PgStat_StatFuncEntry),
 						  fpin) != sizeof(PgStat_StatFuncEntry))
 				{
-					ereport(pgStatRunningInCollector ? LOG : WARNING,
+					ereport(LOG,
 							(errmsg("corrupted statistics file \"%s\"",
 									statfile)));
 					goto done;
 				}
 
-				/*
-				 * Skip if function data not wanted.
-				 */
-				if (funchash == NULL)
-					break;
-
-				funcentry = (PgStat_StatFuncEntry *) hash_search(funchash,
-																 (void *) &funcbuf.functionid,
-																 HASH_ENTER, &found);
+				env = get_stat_entry(PGSTAT_TYPE_TABLE, dbentry->databaseid,
+									 funcbuf.functionid,
+									 false, init_funcentry, &found);
+				funcentry = (PgStat_StatFuncEntry *) &env->body;
 
 				if (found)
 				{
-					ereport(pgStatRunningInCollector ? LOG : WARNING,
+					ereport(LOG,
 							(errmsg("corrupted statistics file \"%s\"",
 									statfile)));
 					goto done;
@@ -5366,7 +5270,7 @@ pgstat_read_db_statsfile(Oid databaseid, HTAB *tabhash, HTAB *funchash,
 				goto done;
 
 			default:
-				ereport(pgStatRunningInCollector ? LOG : WARNING,
+				ereport(LOG,
 						(errmsg("corrupted statistics file \"%s\"",
 								statfile)));
 				goto done;
@@ -5374,292 +5278,15 @@ pgstat_read_db_statsfile(Oid databaseid, HTAB *tabhash, HTAB *funchash,
 	}
 
 done:
-	FreeFile(fpin);
-
-	if (permanent)
-	{
-		elog(DEBUG2, "removing permanent stats file \"%s\"", statfile);
-		unlink(statfile);
-	}
-}
-
-/* ----------
- * pgstat_read_db_statsfile_timestamp() -
- *
- *	Attempt to determine the timestamp of the last db statfile write.
- *	Returns true if successful; the timestamp is stored in *ts.
- *
- *	This needs to be careful about handling databases for which no stats file
- *	exists, such as databases without a stat entry or those not yet written:
- *
- *	- if there's a database entry in the global file, return the corresponding
- *	stats_timestamp value.
- *
- *	- if there's no db stat entry (e.g. for a new or inactive database),
- *	there's no stats_timestamp value, but also nothing to write so we return
- *	the timestamp of the global statfile.
- * ----------
- */
-static bool
-pgstat_read_db_statsfile_timestamp(Oid databaseid, bool permanent,
-								   TimestampTz *ts)
-{
-	PgStat_StatDBEntry dbentry;
-	PgStat_GlobalStats myGlobalStats;
-	PgStat_ArchiverStats myArchiverStats;
-	FILE	   *fpin;
-	int32		format_id;
-	const char *statfile = permanent ? PGSTAT_STAT_PERMANENT_FILENAME : pgstat_stat_filename;
-
-	/*
-	 * Try to open the stats file.  As above, anything but ENOENT is worthy of
-	 * complaining about.
-	 */
-	if ((fpin = AllocateFile(statfile, PG_BINARY_R)) == NULL)
-	{
-		if (errno != ENOENT)
-			ereport(pgStatRunningInCollector ? LOG : WARNING,
-					(errcode_for_file_access(),
-					 errmsg("could not open statistics file \"%s\": %m",
-							statfile)));
-		return false;
-	}
-
-	/*
-	 * Verify it's of the expected format.
-	 */
-	if (fread(&format_id, 1, sizeof(format_id), fpin) != sizeof(format_id) ||
-		format_id != PGSTAT_FILE_FORMAT_ID)
-	{
-		ereport(pgStatRunningInCollector ? LOG : WARNING,
-				(errmsg("corrupted statistics file \"%s\"", statfile)));
-		FreeFile(fpin);
-		return false;
-	}
-
-	/*
-	 * Read global stats struct
-	 */
-	if (fread(&myGlobalStats, 1, sizeof(myGlobalStats),
-			  fpin) != sizeof(myGlobalStats))
-	{
-		ereport(pgStatRunningInCollector ? LOG : WARNING,
-				(errmsg("corrupted statistics file \"%s\"", statfile)));
-		FreeFile(fpin);
-		return false;
-	}
-
-	/*
-	 * Read archiver stats struct
-	 */
-	if (fread(&myArchiverStats, 1, sizeof(myArchiverStats),
-			  fpin) != sizeof(myArchiverStats))
-	{
-		ereport(pgStatRunningInCollector ? LOG : WARNING,
-				(errmsg("corrupted statistics file \"%s\"", statfile)));
-		FreeFile(fpin);
-		return false;
-	}
-
-	/* By default, we're going to return the timestamp of the global file. */
-	*ts = myGlobalStats.stats_timestamp;
-
-	/*
-	 * We found an existing collector stats file.  Read it and look for a
-	 * record for the requested database.  If found, use its timestamp.
-	 */
-	for (;;)
-	{
-		switch (fgetc(fpin))
-		{
-				/*
-				 * 'D'	A PgStat_StatDBEntry struct describing a database
-				 * follows.
-				 */
-			case 'D':
-				if (fread(&dbentry, 1, offsetof(PgStat_StatDBEntry, tables),
-						  fpin) != offsetof(PgStat_StatDBEntry, tables))
-				{
-					ereport(pgStatRunningInCollector ? LOG : WARNING,
-							(errmsg("corrupted statistics file \"%s\"",
-									statfile)));
-					goto done;
-				}
-
-				/*
-				 * If this is the DB we're looking for, save its timestamp and
-				 * we're done.
-				 */
-				if (dbentry.databaseid == databaseid)
-				{
-					*ts = dbentry.stats_timestamp;
-					goto done;
-				}
-
-				break;
-
-			case 'E':
-				goto done;
-
-			default:
-				ereport(pgStatRunningInCollector ? LOG : WARNING,
-						(errmsg("corrupted statistics file \"%s\"",
-								statfile)));
-				goto done;
-		}
-	}
+	if (tabhash)
+		dshash_detach(tabhash);
+	if (funchash)
+		dshash_detach(funchash);
 
-done:
 	FreeFile(fpin);
-	return true;
-}
-
-/*
- * If not already done, read the statistics collector stats file into
- * some hash tables.  The results will be kept until pgstat_clear_snapshot()
- * is called (typically, at end of transaction).
- */
-static void
-backend_read_statsfile(void)
-{
-	TimestampTz min_ts = 0;
-	TimestampTz ref_ts = 0;
-	Oid			inquiry_db;
-	int			count;
-
-	/* already read it? */
-	if (pgStatDBHash)
-		return;
-	Assert(!pgStatRunningInCollector);
-
-	/*
-	 * In a normal backend, we check staleness of the data for our own DB, and
-	 * so we send MyDatabaseId in inquiry messages.  In the autovac launcher,
-	 * check staleness of the shared-catalog data, and send InvalidOid in
-	 * inquiry messages so as not to force writing unnecessary data.
-	 */
-	if (IsAutoVacuumLauncherProcess())
-		inquiry_db = InvalidOid;
-	else
-		inquiry_db = MyDatabaseId;
-
-	/*
-	 * Loop until fresh enough stats file is available or we ran out of time.
-	 * The stats inquiry message is sent repeatedly in case collector drops
-	 * it; but not every single time, as that just swamps the collector.
-	 */
-	for (count = 0; count < PGSTAT_POLL_LOOP_COUNT; count++)
-	{
-		bool		ok;
-		TimestampTz file_ts = 0;
-		TimestampTz cur_ts;
-
-		CHECK_FOR_INTERRUPTS();
-
-		ok = pgstat_read_db_statsfile_timestamp(inquiry_db, false, &file_ts);
-
-		cur_ts = GetCurrentTimestamp();
-		/* Calculate min acceptable timestamp, if we didn't already */
-		if (count == 0 || cur_ts < ref_ts)
-		{
-			/*
-			 * We set the minimum acceptable timestamp to PGSTAT_STAT_INTERVAL
-			 * msec before now.  This indirectly ensures that the collector
-			 * needn't write the file more often than PGSTAT_STAT_INTERVAL. In
-			 * an autovacuum worker, however, we want a lower delay to avoid
-			 * using stale data, so we use PGSTAT_RETRY_DELAY (since the
-			 * number of workers is low, this shouldn't be a problem).
-			 *
-			 * We don't recompute min_ts after sleeping, except in the
-			 * unlikely case that cur_ts went backwards.  So we might end up
-			 * accepting a file a bit older than PGSTAT_STAT_INTERVAL.  In
-			 * practice that shouldn't happen, though, as long as the sleep
-			 * time is less than PGSTAT_STAT_INTERVAL; and we don't want to
-			 * tell the collector that our cutoff time is less than what we'd
-			 * actually accept.
-			 */
-			ref_ts = cur_ts;
-			if (IsAutoVacuumWorkerProcess())
-				min_ts = TimestampTzPlusMilliseconds(ref_ts,
-													 -PGSTAT_RETRY_DELAY);
-			else
-				min_ts = TimestampTzPlusMilliseconds(ref_ts,
-													 -PGSTAT_STAT_INTERVAL);
-		}
-
-		/*
-		 * If the file timestamp is actually newer than cur_ts, we must have
-		 * had a clock glitch (system time went backwards) or there is clock
-		 * skew between our processor and the stats collector's processor.
-		 * Accept the file, but send an inquiry message anyway to make
-		 * pgstat_recv_inquiry do a sanity check on the collector's time.
-		 */
-		if (ok && file_ts > cur_ts)
-		{
-			/*
-			 * A small amount of clock skew between processors isn't terribly
-			 * surprising, but a large difference is worth logging.  We
-			 * arbitrarily define "large" as 1000 msec.
-			 */
-			if (file_ts >= TimestampTzPlusMilliseconds(cur_ts, 1000))
-			{
-				char	   *filetime;
-				char	   *mytime;
-
-				/* Copy because timestamptz_to_str returns a static buffer */
-				filetime = pstrdup(timestamptz_to_str(file_ts));
-				mytime = pstrdup(timestamptz_to_str(cur_ts));
-				elog(LOG, "stats collector's time %s is later than backend local time %s",
-					 filetime, mytime);
-				pfree(filetime);
-				pfree(mytime);
-			}
-
-			pgstat_send_inquiry(cur_ts, min_ts, inquiry_db);
-			break;
-		}
-
-		/* Normal acceptance case: file is not older than cutoff time */
-		if (ok && file_ts >= min_ts)
-			break;
-
-		/* Not there or too old, so kick the collector and wait a bit */
-		if ((count % PGSTAT_INQ_LOOP_COUNT) == 0)
-			pgstat_send_inquiry(cur_ts, min_ts, inquiry_db);
-
-		pg_usleep(PGSTAT_RETRY_DELAY * 1000L);
-	}
-
-	if (count >= PGSTAT_POLL_LOOP_COUNT)
-		ereport(LOG,
-				(errmsg("using stale statistics instead of current ones "
-						"because stats collector is not responding")));
-
-	/*
-	 * Autovacuum launcher wants stats about all databases, but a shallow read
-	 * is sufficient.  Regular backends want a deep read for just the tables
-	 * they can see (MyDatabaseId + shared catalogs).
-	 */
-	if (IsAutoVacuumLauncherProcess())
-		pgStatDBHash = pgstat_read_statsfiles(InvalidOid, false, false);
-	else
-		pgStatDBHash = pgstat_read_statsfiles(MyDatabaseId, false, true);
-}
-
 
-/* ----------
- * pgstat_setup_memcxt() -
- *
- *	Create pgStatLocalContext, if not already done.
- * ----------
- */
-static void
-pgstat_setup_memcxt(void)
-{
-	if (!pgStatLocalContext)
-		pgStatLocalContext = AllocSetContextCreate(TopMemoryContext,
-												   "Statistics snapshot",
-												   ALLOCSET_SMALL_SIZES);
+	elog(DEBUG2, "removing permanent stats file \"%s\"", statfile);
+	unlink(statfile);
 }

@@ -5678,756 +5305,25 @@ pgstat_clear_snapshot(void)
 {
 	/* Release memory, if any was allocated */
 	if (pgStatLocalContext)
+	{
 		MemoryContextDelete(pgStatLocalContext);
 
-	/* Reset variables */
-	pgStatLocalContext = NULL;
-	pgStatDBHash = NULL;
-	localBackendStatusTable = NULL;
-	localNumBackends = 0;
-}
-
-
-/* ----------
- * pgstat_recv_inquiry() -
- *
- *	Process stat inquiry requests.
- * ----------
- */
-static void
-pgstat_recv_inquiry(PgStat_MsgInquiry *msg, int len)
-{
-	PgStat_StatDBEntry *dbentry;
-
-	elog(DEBUG2, "received inquiry for database %u", msg->databaseid);
-
-	/*
-	 * If there's already a write request for this DB, there's nothing to do.
-	 *
-	 * Note that if a request is found, we return early and skip the below
-	 * check for clock skew.  This is okay, since the only way for a DB
-	 * request to be present in the list is that we have been here since the
-	 * last write round.  It seems sufficient to check for clock skew once per
-	 * write round.
-	 */
-	if (list_member_oid(pending_write_requests, msg->databaseid))
-		return;
-
-	/*
-	 * Check to see if we last wrote this database at a time >= the requested
-	 * cutoff time.  If so, this is a stale request that was generated before
-	 * we updated the DB file, and we don't need to do so again.
-	 *
-	 * If the requestor's local clock time is older than stats_timestamp, we
-	 * should suspect a clock glitch, ie system time going backwards; though
-	 * the more likely explanation is just delayed message receipt.  It is
-	 * worth expending a GetCurrentTimestamp call to be sure, since a large
-	 * retreat in the system clock reading could otherwise cause us to neglect
-	 * to update the stats file for a long time.
-	 */
-	dbentry = pgstat_get_db_entry(msg->databaseid, false);
-	if (dbentry == NULL)
-	{
-		/*
-		 * We have no data for this DB.  Enter a write request anyway so that
-		 * the global stats will get updated.  This is needed to prevent
-		 * backend_read_statsfile from waiting for data that we cannot supply,
-		 * in the case of a new DB that nobody has yet reported any stats for.
-		 * See the behavior of pgstat_read_db_statsfile_timestamp.
-		 */
-	}
-	else if (msg->clock_time < dbentry->stats_timestamp)
-	{
-		TimestampTz cur_ts = GetCurrentTimestamp();
-
-		if (cur_ts < dbentry->stats_timestamp)
-		{
-			/*
-			 * Sure enough, time went backwards.  Force a new stats file write
-			 * to get back in sync; but first, log a complaint.
-			 */
-			char	   *writetime;
-			char	   *mytime;
-
-			/* Copy because timestamptz_to_str returns a static buffer */
-			writetime = pstrdup(timestamptz_to_str(dbentry->stats_timestamp));
-			mytime = pstrdup(timestamptz_to_str(cur_ts));
-			elog(LOG,
-				 "stats_timestamp %s is later than collector's time %s for database %u",
-				 writetime, mytime, dbentry->databaseid);
-			pfree(writetime);
-			pfree(mytime);
-		}
-		else
-		{
-			/*
-			 * Nope, it's just an old request.  Assuming msg's clock_time is
-			 * >= its cutoff_time, it must be stale, so we can ignore it.
-			 */
-			return;
-		}
-	}
-	else if (msg->cutoff_time <= dbentry->stats_timestamp)
-	{
-		/* Stale request, ignore it */
-		return;
-	}
-
-	/*
-	 * We need to write this DB, so create a request.
-	 */
-	pending_write_requests = lappend_oid(pending_write_requests,
-										 msg->databaseid);
-}
-
-
-/* ----------
- * pgstat_recv_tabstat() -
- *
- *	Count what the backend has done.
- * ----------
- */
-static void
-pgstat_recv_tabstat(PgStat_MsgTabstat *msg, int len)
-{
-	PgStat_StatDBEntry *dbentry;
-	PgStat_StatTabEntry *tabentry;
-	int			i;
-	bool		found;
-
-	dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-
-	/*
-	 * Update database-wide stats.
-	 */
-	dbentry->n_xact_commit += (PgStat_Counter) (msg->m_xact_commit);
-	dbentry->n_xact_rollback += (PgStat_Counter) (msg->m_xact_rollback);
-	dbentry->n_block_read_time += msg->m_block_read_time;
-	dbentry->n_block_write_time += msg->m_block_write_time;
-
-	/*
-	 * Process all table entries in the message.
-	 */
-	for (i = 0; i < msg->m_nentries; i++)
-	{
-		PgStat_TableEntry *tabmsg = &(msg->m_entry[i]);
-
-		tabentry = (PgStat_StatTabEntry *) hash_search(dbentry->tables,
-													   (void *) &(tabmsg->t_id),
-													   HASH_ENTER, &found);
-
-		if (!found)
-		{
-			/*
-			 * If it's a new table entry, initialize counters to the values we
-			 * just got.
-			 */
-			tabentry->numscans = tabmsg->t_counts.t_numscans;
-			tabentry->tuples_returned = tabmsg->t_counts.t_tuples_returned;
-			tabentry->tuples_fetched = tabmsg->t_counts.t_tuples_fetched;
-			tabentry->tuples_inserted = tabmsg->t_counts.t_tuples_inserted;
-			tabentry->tuples_updated = tabmsg->t_counts.t_tuples_updated;
-			tabentry->tuples_deleted = tabmsg->t_counts.t_tuples_deleted;
-			tabentry->tuples_hot_updated = tabmsg->t_counts.t_tuples_hot_updated;
-			tabentry->n_live_tuples = tabmsg->t_counts.t_delta_live_tuples;
-			tabentry->n_dead_tuples = tabmsg->t_counts.t_delta_dead_tuples;
-			tabentry->changes_since_analyze = tabmsg->t_counts.t_changed_tuples;
-			tabentry->inserts_since_vacuum = tabmsg->t_counts.t_tuples_inserted;
-			tabentry->blocks_fetched = tabmsg->t_counts.t_blocks_fetched;
-			tabentry->blocks_hit = tabmsg->t_counts.t_blocks_hit;
-
-			tabentry->vacuum_timestamp = 0;
-			tabentry->vacuum_count = 0;
-			tabentry->autovac_vacuum_timestamp = 0;
-			tabentry->autovac_vacuum_count = 0;
-			tabentry->analyze_timestamp = 0;
-			tabentry->analyze_count = 0;
-			tabentry->autovac_analyze_timestamp = 0;
-			tabentry->autovac_analyze_count = 0;
-		}
-		else
-		{
-			/*
-			 * Otherwise add the values to the existing entry.
-			 */
-			tabentry->numscans += tabmsg->t_counts.t_numscans;
-			tabentry->tuples_returned += tabmsg->t_counts.t_tuples_returned;
-			tabentry->tuples_fetched += tabmsg->t_counts.t_tuples_fetched;
-			tabentry->tuples_inserted += tabmsg->t_counts.t_tuples_inserted;
-			tabentry->tuples_updated += tabmsg->t_counts.t_tuples_updated;
-			tabentry->tuples_deleted += tabmsg->t_counts.t_tuples_deleted;
-			tabentry->tuples_hot_updated += tabmsg->t_counts.t_tuples_hot_updated;
-			/* If table was truncated, first reset the live/dead counters */
-			if (tabmsg->t_counts.t_truncated)
-			{
-				tabentry->n_live_tuples = 0;
-				tabentry->n_dead_tuples = 0;
-				tabentry->inserts_since_vacuum = 0;
-			}
-			tabentry->n_live_tuples += tabmsg->t_counts.t_delta_live_tuples;
-			tabentry->n_dead_tuples += tabmsg->t_counts.t_delta_dead_tuples;
-			tabentry->changes_since_analyze += tabmsg->t_counts.t_changed_tuples;
-			tabentry->inserts_since_vacuum += tabmsg->t_counts.t_tuples_inserted;
-			tabentry->blocks_fetched += tabmsg->t_counts.t_blocks_fetched;
-			tabentry->blocks_hit += tabmsg->t_counts.t_blocks_hit;
-		}
-
-		/* Clamp n_live_tuples in case of negative delta_live_tuples */
-		tabentry->n_live_tuples = Max(tabentry->n_live_tuples, 0);
-		/* Likewise for n_dead_tuples */
-		tabentry->n_dead_tuples = Max(tabentry->n_dead_tuples, 0);
-
-		/*
-		 * Add per-table stats to the per-database entry, too.
-		 */
-		dbentry->n_tuples_returned += tabmsg->t_counts.t_tuples_returned;
-		dbentry->n_tuples_fetched += tabmsg->t_counts.t_tuples_fetched;
-		dbentry->n_tuples_inserted += tabmsg->t_counts.t_tuples_inserted;
-		dbentry->n_tuples_updated += tabmsg->t_counts.t_tuples_updated;
-		dbentry->n_tuples_deleted += tabmsg->t_counts.t_tuples_deleted;
-		dbentry->n_blocks_fetched += tabmsg->t_counts.t_blocks_fetched;
-		dbentry->n_blocks_hit += tabmsg->t_counts.t_blocks_hit;
-	}
-}
-
-
-/* ----------
- * pgstat_recv_tabpurge() -
- *
- *	Arrange for dead table removal.
- * ----------
- */
-static void
-pgstat_recv_tabpurge(PgStat_MsgTabpurge *msg, int len)
-{
-	PgStat_StatDBEntry *dbentry;
-	int			i;
-
-	dbentry = pgstat_get_db_entry(msg->m_databaseid, false);
-
-	/*
-	 * No need to purge if we don't even know the database.
-	 */
-	if (!dbentry || !dbentry->tables)
-		return;
-
-	/*
-	 * Process all table entries in the message.
-	 */
-	for (i = 0; i < msg->m_nentries; i++)
-	{
-		/* Remove from hashtable if present; we don't care if it's not. */
-		(void) hash_search(dbentry->tables,
-						   (void *) &(msg->m_tableid[i]),
-						   HASH_REMOVE, NULL);
-	}
-}
-
-
-/* ----------
- * pgstat_recv_dropdb() -
- *
- *	Arrange for dead database removal
- * ----------
- */
-static void
-pgstat_recv_dropdb(PgStat_MsgDropdb *msg, int len)
-{
-	Oid			dbid = msg->m_databaseid;
-	PgStat_StatDBEntry *dbentry;
-
-	/*
-	 * Lookup the database in the hashtable.
-	 */
-	dbentry = pgstat_get_db_entry(dbid, false);
-
-	/*
-	 * If found, remove it (along with the db statfile).
-	 */
-	if (dbentry)
-	{
-		char		statfile[MAXPGPATH];
-
-		get_dbstat_filename(false, false, dbid, statfile, MAXPGPATH);
-
-		elog(DEBUG2, "removing stats file \"%s\"", statfile);
-		unlink(statfile);
-
-		if (dbentry->tables != NULL)
-			hash_destroy(dbentry->tables);
-		if (dbentry->functions != NULL)
-			hash_destroy(dbentry->functions);
-
-		if (hash_search(pgStatDBHash,
-						(void *) &dbid,
-						HASH_REMOVE, NULL) == NULL)
-			ereport(ERROR,
-					(errmsg("database hash table corrupted during cleanup --- abort")));
-	}
-}
-
-
-/* ----------
- * pgstat_recv_resetcounter() -
- *
- *	Reset the statistics for the specified database.
- * ----------
- */
-static void
-pgstat_recv_resetcounter(PgStat_MsgResetcounter *msg, int len)
-{
-	PgStat_StatDBEntry *dbentry;
-
-	/*
-	 * Lookup the database in the hashtable.  Nothing to do if not there.
-	 */
-	dbentry = pgstat_get_db_entry(msg->m_databaseid, false);
-
-	if (!dbentry)
-		return;
-
-	/*
-	 * We simply throw away all the database's table entries by recreating a
-	 * new hash table for them.
-	 */
-	if (dbentry->tables != NULL)
-		hash_destroy(dbentry->tables);
-	if (dbentry->functions != NULL)
-		hash_destroy(dbentry->functions);
-
-	dbentry->tables = NULL;
-	dbentry->functions = NULL;
-
-	/*
-	 * Reset database-level stats, too.  This creates empty hash tables for
-	 * tables and functions.
-	 */
-	reset_dbentry_counters(dbentry);
-}
-
-/* ----------
- * pgstat_recv_resetsharedcounter() -
- *
- *	Reset some shared statistics of the cluster.
- * ----------
- */
-static void
-pgstat_recv_resetsharedcounter(PgStat_MsgResetsharedcounter *msg, int len)
-{
-	if (msg->m_resettarget == RESET_BGWRITER)
-	{
-		/* Reset the global background writer statistics for the cluster. */
-		memset(&globalStats, 0, sizeof(globalStats));
-		globalStats.stat_reset_timestamp = GetCurrentTimestamp();
-	}
-	else if (msg->m_resettarget == RESET_ARCHIVER)
-	{
-		/* Reset the archiver statistics for the cluster. */
-		memset(&archiverStats, 0, sizeof(archiverStats));
-		archiverStats.stat_reset_timestamp = GetCurrentTimestamp();
-	}
-
-	/*
-	 * Presumably the sender of this message validated the target, don't
-	 * complain here if it's not valid
-	 */
-}
-
-/* ----------
- * pgstat_recv_resetsinglecounter() -
- *
- *	Reset a statistics for a single object
- * ----------
- */
-static void
-pgstat_recv_resetsinglecounter(PgStat_MsgResetsinglecounter *msg, int len)
-{
-	PgStat_StatDBEntry *dbentry;
-
-	dbentry = pgstat_get_db_entry(msg->m_databaseid, false);
-
-	if (!dbentry)
-		return;
-
-	/* Set the reset timestamp for the whole database */
-	dbentry->stat_reset_timestamp = GetCurrentTimestamp();
-
-	/* Remove object if it exists, ignore it if not */
-	if (msg->m_resettype == RESET_TABLE)
-		(void) hash_search(dbentry->tables, (void *) &(msg->m_objectid),
-						   HASH_REMOVE, NULL);
-	else if (msg->m_resettype == RESET_FUNCTION)
-		(void) hash_search(dbentry->functions, (void *) &(msg->m_objectid),
-						   HASH_REMOVE, NULL);
-}
-
-/* ----------
- * pgstat_recv_autovac() -
- *
- *	Process an autovacuum signalling message.
- * ----------
- */
-static void
-pgstat_recv_autovac(PgStat_MsgAutovacStart *msg, int len)
-{
-	PgStat_StatDBEntry *dbentry;
-
-	/*
-	 * Store the last autovacuum time in the database's hashtable entry.
-	 */
-	dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-
-	dbentry->last_autovac_time = msg->m_start_time;
-}
-
-/* ----------
- * pgstat_recv_vacuum() -
- *
- *	Process a VACUUM message.
- * ----------
- */
-static void
-pgstat_recv_vacuum(PgStat_MsgVacuum *msg, int len)
-{
-	PgStat_StatDBEntry *dbentry;
-	PgStat_StatTabEntry *tabentry;
-
-	/*
-	 * Store the data in the table's hashtable entry.
-	 */
-	dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-
-	tabentry = pgstat_get_tab_entry(dbentry, msg->m_tableoid, true);
-
-	tabentry->n_live_tuples = msg->m_live_tuples;
-	tabentry->n_dead_tuples = msg->m_dead_tuples;
-
-	/*
-	 * It is quite possible that a non-aggressive VACUUM ended up skipping
-	 * various pages, however, we'll zero the insert counter here regardless.
-	 * It's currently used only to track when we need to perform an
-	 * "insert" autovacuum, which are mainly intended to freeze newly inserted
-	 * tuples.  Zeroing this may just mean we'll not try to vacuum the table
-	 * again until enough tuples have been inserted to trigger another insert
-	 * autovacuum.  An anti-wraparound autovacuum will catch any persistent
-	 * stragglers.
-	 */
-	tabentry->inserts_since_vacuum = 0;
-
-	if (msg->m_autovacuum)
-	{
-		tabentry->autovac_vacuum_timestamp = msg->m_vacuumtime;
-		tabentry->autovac_vacuum_count++;
+		/* Reset variables */
+		pgStatLocalContext = NULL;
+		localBackendStatusTable = NULL;
+		localNumBackends = 0;
 	}
-	else
-	{
-		tabentry->vacuum_timestamp = msg->m_vacuumtime;
-		tabentry->vacuum_count++;
-	}
-}
-
-/* ----------
- * pgstat_recv_analyze() -
- *
- *	Process an ANALYZE message.
- * ----------
- */
-static void
-pgstat_recv_analyze(PgStat_MsgAnalyze *msg, int len)
-{
-	PgStat_StatDBEntry *dbentry;
-	PgStat_StatTabEntry *tabentry;
 
-	/*
-	 * Store the data in the table's hashtable entry.
-	 */
-	dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-
-	tabentry = pgstat_get_tab_entry(dbentry, msg->m_tableoid, true);
-
-	tabentry->n_live_tuples = msg->m_live_tuples;
-	tabentry->n_dead_tuples = msg->m_dead_tuples;
-
-	/*
-	 * If commanded, reset changes_since_analyze to zero.  This forgets any
-	 * changes that were committed while the ANALYZE was in progress, but we
-	 * have no good way to estimate how many of those there were.
-	 */
-	if (msg->m_resetcounter)
-		tabentry->changes_since_analyze = 0;
-
-	if (msg->m_autovacuum)
+	if (pgStatSnapshotContext)
 	{
-		tabentry->autovac_analyze_timestamp = msg->m_analyzetime;
-		tabentry->autovac_analyze_count++;
-	}
-	else
-	{
-		tabentry->analyze_timestamp = msg->m_analyzetime;
-		tabentry->analyze_count++;
-	}
-}
-
+		MemoryContextReset(pgStatSnapshotContext);
 
-/* ----------
- * pgstat_recv_archiver() -
- *
- *	Process a ARCHIVER message.
- * ----------
- */
-static void
-pgstat_recv_archiver(PgStat_MsgArchiver *msg, int len)
-{
-	if (msg->m_failed)
-	{
-		/* Failed archival attempt */
-		++archiverStats.failed_count;
-		memcpy(archiverStats.last_failed_wal, msg->m_xlog,
-			   sizeof(archiverStats.last_failed_wal));
-		archiverStats.last_failed_timestamp = msg->m_timestamp;
-	}
-	else
-	{
-		/* Successful archival operation */
-		++archiverStats.archived_count;
-		memcpy(archiverStats.last_archived_wal, msg->m_xlog,
-			   sizeof(archiverStats.last_archived_wal));
-		archiverStats.last_archived_timestamp = msg->m_timestamp;
+		/* Reset variables that pointed to the context */
+		global_snapshot_is_valid = false;
+		pgStatSnapshotHash = NULL;
 	}
 }
 
-/* ----------
- * pgstat_recv_bgwriter() -
- *
- *	Process a BGWRITER message.
- * ----------
- */
-static void
-pgstat_recv_bgwriter(PgStat_MsgBgWriter *msg, int len)
-{
-	globalStats.timed_checkpoints += msg->m_timed_checkpoints;
-	globalStats.requested_checkpoints += msg->m_requested_checkpoints;
-	globalStats.checkpoint_write_time += msg->m_checkpoint_write_time;
-	globalStats.checkpoint_sync_time += msg->m_checkpoint_sync_time;
-	globalStats.buf_written_checkpoints += msg->m_buf_written_checkpoints;
-	globalStats.buf_written_clean += msg->m_buf_written_clean;
-	globalStats.maxwritten_clean += msg->m_maxwritten_clean;
-	globalStats.buf_written_backend += msg->m_buf_written_backend;
-	globalStats.buf_fsync_backend += msg->m_buf_fsync_backend;
-	globalStats.buf_alloc += msg->m_buf_alloc;
-}
-
-/* ----------
- * pgstat_recv_recoveryconflict() -
- *
- *	Process a RECOVERYCONFLICT message.
- * ----------
- */
-static void
-pgstat_recv_recoveryconflict(PgStat_MsgRecoveryConflict *msg, int len)
-{
-	PgStat_StatDBEntry *dbentry;
-
-	dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-
-	switch (msg->m_reason)
-	{
-		case PROCSIG_RECOVERY_CONFLICT_DATABASE:
-
-			/*
-			 * Since we drop the information about the database as soon as it
-			 * replicates, there is no point in counting these conflicts.
-			 */
-			break;
-		case PROCSIG_RECOVERY_CONFLICT_TABLESPACE:
-			dbentry->n_conflict_tablespace++;
-			break;
-		case PROCSIG_RECOVERY_CONFLICT_LOCK:
-			dbentry->n_conflict_lock++;
-			break;
-		case PROCSIG_RECOVERY_CONFLICT_SNAPSHOT:
-			dbentry->n_conflict_snapshot++;
-			break;
-		case PROCSIG_RECOVERY_CONFLICT_BUFFERPIN:
-			dbentry->n_conflict_bufferpin++;
-			break;
-		case PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK:
-			dbentry->n_conflict_startup_deadlock++;
-			break;
-	}
-}
-
-/* ----------
- * pgstat_recv_deadlock() -
- *
- *	Process a DEADLOCK message.
- * ----------
- */
-static void
-pgstat_recv_deadlock(PgStat_MsgDeadlock *msg, int len)
-{
-	PgStat_StatDBEntry *dbentry;
-
-	dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-
-	dbentry->n_deadlocks++;
-}
-
-/* ----------
- * pgstat_recv_checksum_failure() -
- *
- *	Process a CHECKSUMFAILURE message.
- * ----------
- */
-static void
-pgstat_recv_checksum_failure(PgStat_MsgChecksumFailure *msg, int len)
-{
-	PgStat_StatDBEntry *dbentry;
-
-	dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-
-	dbentry->n_checksum_failures += msg->m_failurecount;
-	dbentry->last_checksum_failure = msg->m_failure_time;
-}
-
-/* ----------
- * pgstat_recv_tempfile() -
- *
- *	Process a TEMPFILE message.
- * ----------
- */
-static void
-pgstat_recv_tempfile(PgStat_MsgTempFile *msg, int len)
-{
-	PgStat_StatDBEntry *dbentry;
-
-	dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-
-	dbentry->n_temp_bytes += msg->m_filesize;
-	dbentry->n_temp_files += 1;
-}
-
-/* ----------
- * pgstat_recv_funcstat() -
- *
- *	Count what the backend has done.
- * ----------
- */
-static void
-pgstat_recv_funcstat(PgStat_MsgFuncstat *msg, int len)
-{
-	PgStat_FunctionEntry *funcmsg = &(msg->m_entry[0]);
-	PgStat_StatDBEntry *dbentry;
-	PgStat_StatFuncEntry *funcentry;
-	int			i;
-	bool		found;
-
-	dbentry = pgstat_get_db_entry(msg->m_databaseid, true);
-
-	/*
-	 * Process all function entries in the message.
-	 */
-	for (i = 0; i < msg->m_nentries; i++, funcmsg++)
-	{
-		funcentry = (PgStat_StatFuncEntry *) hash_search(dbentry->functions,
-														 (void *) &(funcmsg->f_id),
-														 HASH_ENTER, &found);
-
-		if (!found)
-		{
-			/*
-			 * If it's a new function entry, initialize counters to the values
-			 * we just got.
-			 */
-			funcentry->f_numcalls = funcmsg->f_numcalls;
-			funcentry->f_total_time = funcmsg->f_total_time;
-			funcentry->f_self_time = funcmsg->f_self_time;
-		}
-		else
-		{
-			/*
-			 * Otherwise add the values to the existing entry.
-			 */
-			funcentry->f_numcalls += funcmsg->f_numcalls;
-			funcentry->f_total_time += funcmsg->f_total_time;
-			funcentry->f_self_time += funcmsg->f_self_time;
-		}
-	}
-}
-
-/* ----------
- * pgstat_recv_funcpurge() -
- *
- *	Arrange for dead function removal.
- * ----------
- */
-static void
-pgstat_recv_funcpurge(PgStat_MsgFuncpurge *msg, int len)
-{
-	PgStat_StatDBEntry *dbentry;
-	int			i;
-
-	dbentry = pgstat_get_db_entry(msg->m_databaseid, false);
-
-	/*
-	 * No need to purge if we don't even know the database.
-	 */
-	if (!dbentry || !dbentry->functions)
-		return;
-
-	/*
-	 * Process all function entries in the message.
-	 */
-	for (i = 0; i < msg->m_nentries; i++)
-	{
-		/* Remove from hashtable if present; we don't care if it's not. */
-		(void) hash_search(dbentry->functions,
-						   (void *) &(msg->m_functionid[i]),
-						   HASH_REMOVE, NULL);
-	}
-}
-
-/* ----------
- * pgstat_write_statsfile_needed() -
- *
- *	Do we need to write out any stats files?
- * ----------
- */
-static bool
-pgstat_write_statsfile_needed(void)
-{
-	if (pending_write_requests != NIL)
-		return true;
-
-	/* Everything was written recently */
-	return false;
-}
-
-/* ----------
- * pgstat_db_requested() -
- *
- *	Checks whether stats for a particular DB need to be written to a file.
- * ----------
- */
-static bool
-pgstat_db_requested(Oid databaseid)
-{
-	/*
-	 * If any requests are outstanding at all, we should write the stats for
-	 * shared catalogs (the "database" with OID 0).  This ensures that
-	 * backends will see up-to-date stats for shared catalogs, even though
-	 * they send inquiry messages mentioning only their own DB.
-	 */
-	if (databaseid == InvalidOid && pending_write_requests != NIL)
-		return true;
-
-	/* Search to see if there's an open request to write this database. */
-	if (list_member_oid(pending_write_requests, databaseid))
-		return true;
-
-	return false;
-}
-
 /*
  * Convert a potentially unsafely truncated activity string (see
  * PgBackendStatus.st_activity_raw's documentation) into a correctly truncated
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index a4b9d212a2..83ca2c1113 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -255,7 +255,6 @@ static pid_t StartupPID = 0,
 			WalReceiverPID = 0,
 			AutoVacPID = 0,
 			PgArchPID = 0,
-			PgStatPID = 0,
 			SysLoggerPID = 0;
 
 /* Startup process's status */
@@ -503,7 +502,6 @@ typedef struct
 	PGPROC	   *AuxiliaryProcs;
 	PGPROC	   *PreparedXactProcs;
 	PMSignalData *PMSignalState;
-	InheritableSocket pgStatSock;
 	pid_t		PostmasterPid;
 	TimestampTz PgStartTime;
 	TimestampTz PgReloadTime;
@@ -1326,12 +1324,6 @@ PostmasterMain(int argc, char *argv[])
 	 */
 	RemovePgTempFiles();
 
-	/*
-	 * Initialize stats collection subsystem (this does NOT start the
-	 * collector process!)
-	 */
-	pgstat_init();
-
 	/*
 	 * Initialize the autovacuum subsystem (again, no process start yet)
 	 */
@@ -1780,11 +1772,6 @@ ServerLoop(void)
 				start_autovac_launcher = false; /* signal processed */
 		}
 
-		/* If we have lost the stats collector, try to start a new one */
-		if (PgStatPID == 0 &&
-			(pmState == PM_RUN || pmState == PM_HOT_STANDBY))
-			PgStatPID = pgstat_start();
-
 		/* If we have lost the archiver, try to start a new one. */
 		if (PgArchPID == 0 && PgArchStartupAllowed())
 			PgArchPID = StartArchiver();
@@ -2694,8 +2681,6 @@ SIGHUP_handler(SIGNAL_ARGS)
 			signal_child(PgArchPID, SIGHUP);
 		if (SysLoggerPID != 0)
 			signal_child(SysLoggerPID, SIGHUP);
-		if (PgStatPID != 0)
-			signal_child(PgStatPID, SIGHUP);
 
 		/* Reload authentication config files too */
 		if (!load_hba())
@@ -3058,8 +3043,6 @@ reaper(SIGNAL_ARGS)
 				AutoVacPID = StartAutoVacLauncher();
 			if (PgArchStartupAllowed() && PgArchPID == 0)
 				PgArchPID = StartArchiver();
-			if (PgStatPID == 0)
-				PgStatPID = pgstat_start();
 
 			/* workers may be scheduled to start now */
 			maybe_start_bgworkers();
@@ -3126,13 +3109,6 @@ reaper(SIGNAL_ARGS)
 				SignalChildren(SIGUSR2);
 
 				pmState = PM_SHUTDOWN_2;
-
-				/*
-				 * We can also shut down the stats collector now; there's
-				 * nothing left for it to do.
-				 */
-				if (PgStatPID != 0)
-					signal_child(PgStatPID, SIGQUIT);
 			}
 			else
 			{
@@ -3205,22 +3181,6 @@ reaper(SIGNAL_ARGS)
 			continue;
 		}
 
-		/*
-		 * Was it the statistics collector?  If so, just try to start a new
-		 * one; no need to force reset of the rest of the system.  (If fail,
-		 * we'll try again in future cycles of the main loop.)
-		 */
-		if (pid == PgStatPID)
-		{
-			PgStatPID = 0;
-			if (!EXIT_STATUS_0(exitstatus))
-				LogChildExit(LOG, _("statistics collector process"),
-							 pid, exitstatus);
-			if (pmState == PM_RUN || pmState == PM_HOT_STANDBY)
-				PgStatPID = pgstat_start();
-			continue;
-		}
-
 		/* Was it the system logger?  If so, try to start a new one */
 		if (pid == SysLoggerPID)
 		{
@@ -3681,22 +3641,6 @@ HandleChildCrash(int pid, int exitstatus, const char *procname)
 		signal_child(PgArchPID, SIGQUIT);
 	}
 
-	/*
-	 * Force a power-cycle of the pgstat process too.  (This isn't absolutely
-	 * necessary, but it seems like a good idea for robustness, and it
-	 * simplifies the state-machine logic in the case where a shutdown request
-	 * arrives during crash processing.)
-	 */
-	if (PgStatPID != 0 && take_action)
-	{
-		ereport(DEBUG2,
-				(errmsg_internal("sending %s to process %d",
-								 "SIGQUIT",
-								 (int) PgStatPID)));
-		signal_child(PgStatPID, SIGQUIT);
-		allow_immediate_pgstat_restart();
-	}
-
 	/* We do NOT restart the syslogger */
 
 	if (Shutdown != ImmediateShutdown)
@@ -3892,8 +3836,6 @@ PostmasterStateMachine(void)
 					SignalChildren(SIGQUIT);
 					if (PgArchPID != 0)
 						signal_child(PgArchPID, SIGQUIT);
-					if (PgStatPID != 0)
-						signal_child(PgStatPID, SIGQUIT);
 				}
 			}
 		}
@@ -3928,8 +3870,7 @@ PostmasterStateMachine(void)
 		 * normal state transition leading up to PM_WAIT_DEAD_END, or during
 		 * FatalError processing.
 		 */
-		if (dlist_is_empty(&BackendList) &&
-			PgArchPID == 0 && PgStatPID == 0)
+		if (dlist_is_empty(&BackendList) && PgArchPID == 0)
 		{
 			/* These other guys should be dead already */
 			Assert(StartupPID == 0);
@@ -4130,8 +4071,6 @@ TerminateChildren(int signal)
 		signal_child(AutoVacPID, signal);
 	if (PgArchPID != 0)
 		signal_child(PgArchPID, signal);
-	if (PgStatPID != 0)
-		signal_child(PgStatPID, signal);
 }
 
 /*
@@ -5109,18 +5048,6 @@ SubPostmasterMain(int argc, char *argv[])
 
 		StartBackgroundWorker();
 	}
-	if (strcmp(argv[1], "--forkarch") == 0)
-	{
-		/* Do not want to attach to shared memory */
-
-		PgArchiverMain(argc, argv); /* does not return */
-	}
-	if (strcmp(argv[1], "--forkcol") == 0)
-	{
-		/* Do not want to attach to shared memory */
-
-		PgstatCollectorMain(argc, argv);	/* does not return */
-	}
 	if (strcmp(argv[1], "--forklog") == 0)
 	{
 		/* Do not want to attach to shared memory */
@@ -5239,12 +5166,6 @@ sigusr1_handler(SIGNAL_ARGS)
 	if (CheckPostmasterSignal(PMSIGNAL_BEGIN_HOT_STANDBY) &&
 		pmState == PM_RECOVERY && Shutdown == NoShutdown)
 	{
-		/*
-		 * Likewise, start other special children as needed.
-		 */
-		Assert(PgStatPID == 0);
-		PgStatPID = pgstat_start();
-
 		ereport(LOG,
 				(errmsg("database system is ready to accept read only connections")));
 
@@ -6139,7 +6060,6 @@ extern slock_t *ShmemLock;
 extern slock_t *ProcStructLock;
 extern PGPROC *AuxiliaryProcs;
 extern PMSignalData *PMSignalState;
-extern pgsocket pgStatSock;
 extern pg_time_t first_syslogger_file_time;
 
 #ifndef WIN32
@@ -6195,8 +6115,6 @@ save_backend_variables(BackendParameters *param, Port *port,
 	param->AuxiliaryProcs = AuxiliaryProcs;
 	param->PreparedXactProcs = PreparedXactProcs;
 	param->PMSignalState = PMSignalState;
-	if (!write_inheritable_socket(&param->pgStatSock, pgStatSock, childPid))
-		return false;
 
 	param->PostmasterPid = PostmasterPid;
 	param->PgStartTime = PgStartTime;
@@ -6431,7 +6349,6 @@ restore_backend_variables(BackendParameters *param, Port *port)
 	AuxiliaryProcs = param->AuxiliaryProcs;
 	PreparedXactProcs = param->PreparedXactProcs;
 	PMSignalState = param->PMSignalState;
-	read_inheritable_socket(&pgStatSock, &param->pgStatSock);
 
 	PostmasterPid = param->PostmasterPid;
 	PgStartTime = param->PgStartTime;
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index e05e2b3456..26414dadb2 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -1947,7 +1947,7 @@ BufferSync(int flags)
 			if (SyncOneBuffer(buf_id, false, &wb_context) & BUF_WRITTEN)
 			{
 				TRACE_POSTGRESQL_BUFFER_SYNC_WRITTEN(buf_id);
-				BgWriterStats.m_buf_written_checkpoints++;
+				BgWriterStats.buf_written_checkpoints++;
 				num_written++;
 			}
 		}
@@ -2057,7 +2057,7 @@ BgBufferSync(WritebackContext *wb_context)
 	strategy_buf_id = StrategySyncStart(&strategy_passes, &recent_alloc);
 
 	/* Report buffer alloc counts to pgstat */
-	BgWriterStats.m_buf_alloc += recent_alloc;
+	BgWriterStats.buf_alloc += recent_alloc;
 
 	/*
 	 * If we're not running the LRU scan, just stop after doing the stats
@@ -2247,7 +2247,7 @@ BgBufferSync(WritebackContext *wb_context)
 			reusable_buffers++;
 			if (++num_written >= bgwriter_lru_maxpages)
 			{
-				BgWriterStats.m_maxwritten_clean++;
+				BgWriterStats.maxwritten_clean++;
 				break;
 			}
 		}
@@ -2255,7 +2255,7 @@ BgBufferSync(WritebackContext *wb_context)
 			reusable_buffers++;
 	}
 
-	BgWriterStats.m_buf_written_clean += num_written;
+	BgWriterStats.buf_written_clean += num_written;
 
 #ifdef BGW_DEBUG
 	elog(DEBUG1, "bgwriter: recent_alloc=%u smoothed=%.2f delta=%ld ahead=%d density=%.2f reusable_est=%d upcoming_est=%d scanned=%d wrote=%d reusable=%d",
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 427b0d59cd..58a442f482 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -147,6 +147,7 @@ CreateSharedMemoryAndSemaphores(void)
 		size = add_size(size, BTreeShmemSize());
 		size = add_size(size, SyncScanShmemSize());
 		size = add_size(size, AsyncShmemSize());
+		size = add_size(size, StatsShmemSize());
 #ifdef EXEC_BACKEND
 		size = add_size(size, ShmemBackendArraySize());
 #endif
@@ -263,6 +264,7 @@ CreateSharedMemoryAndSemaphores(void)
 	BTreeShmemInit();
 	SyncScanShmemInit();
 	AsyncShmemInit();
+	StatsShmemInit();
 
 #ifdef EXEC_BACKEND
 
diff --git a/src/backend/storage/lmgr/lwlock.c b/src/backend/storage/lmgr/lwlock.c
index 4c14e51c67..f61fd3e8ad 100644
--- a/src/backend/storage/lmgr/lwlock.c
+++ b/src/backend/storage/lmgr/lwlock.c
@@ -523,6 +523,7 @@ RegisterLWLockTranches(void)
 	LWLockRegisterTranche(LWTRANCHE_PARALLEL_APPEND, "parallel_append");
 	LWLockRegisterTranche(LWTRANCHE_PARALLEL_HASH_JOIN, "parallel_hash_join");
 	LWLockRegisterTranche(LWTRANCHE_SXACT, "serializable_xact");
+	LWLockRegisterTranche(LWTRANCHE_STATS, "activity_statistics");
 
 	/* Register named tranches. */
 	for (i = 0; i < NamedLWLockTrancheRequests; i++)
diff --git a/src/backend/storage/lmgr/lwlocknames.txt b/src/backend/storage/lmgr/lwlocknames.txt
index db47843229..97eccb35d3 100644
--- a/src/backend/storage/lmgr/lwlocknames.txt
+++ b/src/backend/storage/lmgr/lwlocknames.txt
@@ -49,3 +49,4 @@ MultiXactTruncationLock				41
 OldSnapshotTimeMapLock				42
 LogicalRepWorkerLock				43
 CLogTruncationLock					44
+StatsLock							45
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index cb8c23e4b7..29b9b8d9fc 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -3189,6 +3189,12 @@ ProcessInterrupts(void)
 
 	if (ParallelMessagePending)
 		HandleParallelMessages();
+
+	if (IdleStatsUpdateTimeoutPending)
+	{
+		IdleStatsUpdateTimeoutPending = false;
+		pgstat_report_stat(true);
+	}
 }

@@ -3763,6 +3769,7 @@ PostgresMain(int argc, char *argv[],
 	sigjmp_buf	local_sigjmp_buf;
 	volatile bool send_ready_for_query = true;
 	bool		disable_idle_in_transaction_timeout = false;
+	bool		disable_idle_stats_update_timeout = false;
 
 	/* Initialize startup process environment if necessary. */
 	if (!IsUnderPostmaster)
@@ -4201,6 +4208,8 @@ PostgresMain(int argc, char *argv[],
 			}
 			else
 			{
+				long stats_timeout;
+
 				/* Send out notify signals and transmit self-notifies */
 				ProcessCompletedNotifies();
 
@@ -4213,8 +4222,13 @@ PostgresMain(int argc, char *argv[],
 				if (notifyInterruptPending)
 					ProcessNotifyInterrupt();
 
-				pgstat_report_stat(false);
-
+				stats_timeout = pgstat_report_stat(false);
+				if (stats_timeout > 0)
+				{
+					disable_idle_stats_update_timeout = true;
+					enable_timeout_after(IDLE_STATS_UPDATE_TIMEOUT,
+										 stats_timeout);
+				}
 				set_ps_display("idle");
 				pgstat_report_activity(STATE_IDLE, NULL);
 			}
@@ -4249,7 +4263,7 @@ PostgresMain(int argc, char *argv[],
 		DoingCommandRead = false;
 
 		/*
-		 * (5) turn off the idle-in-transaction timeout
+		 * (5) turn off the idle-in-transaction timeout and stats update timeout
 		 */
 		if (disable_idle_in_transaction_timeout)
 		{
@@ -4257,6 +4271,12 @@ PostgresMain(int argc, char *argv[],
 			disable_idle_in_transaction_timeout = false;
 		}
 
+		if (disable_idle_stats_update_timeout)
+		{
+			disable_timeout(IDLE_STATS_UPDATE_TIMEOUT, false);
+			disable_idle_stats_update_timeout = false;
+		}
+
 		/*
 		 * (6) check for any other interesting events that happened while we
 		 * slept.
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 6d66ff8b44..b59b22c367 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -33,9 +33,6 @@
 
 #define UINT32_ACCESS_ONCE(var)		 ((uint32)(*((volatile uint32 *)&(var))))
 
-/* Global bgwriter statistics, from bgwriter.c */
-extern PgStat_MsgBgWriter bgwriterStats;
-
 Datum
 pg_stat_get_numscans(PG_FUNCTION_ARGS)
 {
@@ -1260,7 +1257,7 @@ pg_stat_get_db_xact_commit(PG_FUNCTION_ARGS)
 	if ((dbentry = pgstat_fetch_stat_dbentry(dbid)) == NULL)
 		result = 0;
 	else
-		result = (int64) (dbentry->n_xact_commit);
+		result = (int64) (dbentry->counts.n_xact_commit);
 
 	PG_RETURN_INT64(result);
 }
@@ -1276,7 +1273,7 @@ pg_stat_get_db_xact_rollback(PG_FUNCTION_ARGS)
 	if ((dbentry = pgstat_fetch_stat_dbentry(dbid)) == NULL)
 		result = 0;
 	else
-		result = (int64) (dbentry->n_xact_rollback);
+		result = (int64) (dbentry->counts.n_xact_rollback);
 
 	PG_RETURN_INT64(result);
 }
@@ -1292,7 +1289,7 @@ pg_stat_get_db_blocks_fetched(PG_FUNCTION_ARGS)
 	if ((dbentry = pgstat_fetch_stat_dbentry(dbid)) == NULL)
 		result = 0;
 	else
-		result = (int64) (dbentry->n_blocks_fetched);
+		result = (int64) (dbentry->counts.n_blocks_fetched);
 
 	PG_RETURN_INT64(result);
 }
@@ -1308,7 +1305,7 @@ pg_stat_get_db_blocks_hit(PG_FUNCTION_ARGS)
 	if ((dbentry = pgstat_fetch_stat_dbentry(dbid)) == NULL)
 		result = 0;
 	else
-		result = (int64) (dbentry->n_blocks_hit);
+		result = (int64) (dbentry->counts.n_blocks_hit);
 
 	PG_RETURN_INT64(result);
 }
@@ -1324,7 +1321,7 @@ pg_stat_get_db_tuples_returned(PG_FUNCTION_ARGS)
 	if ((dbentry = pgstat_fetch_stat_dbentry(dbid)) == NULL)
 		result = 0;
 	else
-		result = (int64) (dbentry->n_tuples_returned);
+		result = (int64) (dbentry->counts.n_tuples_returned);
 
 	PG_RETURN_INT64(result);
 }
@@ -1340,7 +1337,7 @@ pg_stat_get_db_tuples_fetched(PG_FUNCTION_ARGS)
 	if ((dbentry = pgstat_fetch_stat_dbentry(dbid)) == NULL)
 		result = 0;
 	else
-		result = (int64) (dbentry->n_tuples_fetched);
+		result = (int64) (dbentry->counts.n_tuples_fetched);
 
 	PG_RETURN_INT64(result);
 }
@@ -1356,7 +1353,7 @@ pg_stat_get_db_tuples_inserted(PG_FUNCTION_ARGS)
 	if ((dbentry = pgstat_fetch_stat_dbentry(dbid)) == NULL)
 		result = 0;
 	else
-		result = (int64) (dbentry->n_tuples_inserted);
+		result = (int64) (dbentry->counts.n_tuples_inserted);
 
 	PG_RETURN_INT64(result);
 }
@@ -1372,7 +1369,7 @@ pg_stat_get_db_tuples_updated(PG_FUNCTION_ARGS)
 	if ((dbentry = pgstat_fetch_stat_dbentry(dbid)) == NULL)
 		result = 0;
 	else
-		result = (int64) (dbentry->n_tuples_updated);
+		result = (int64) (dbentry->counts.n_tuples_updated);
 
 	PG_RETURN_INT64(result);
 }
@@ -1388,7 +1385,7 @@ pg_stat_get_db_tuples_deleted(PG_FUNCTION_ARGS)
 	if ((dbentry = pgstat_fetch_stat_dbentry(dbid)) == NULL)
 		result = 0;
 	else
-		result = (int64) (dbentry->n_tuples_deleted);
+		result = (int64) (dbentry->counts.n_tuples_deleted);
 
 	PG_RETURN_INT64(result);
 }
@@ -1421,7 +1418,7 @@ pg_stat_get_db_temp_files(PG_FUNCTION_ARGS)
 	if ((dbentry = pgstat_fetch_stat_dbentry(dbid)) == NULL)
 		result = 0;
 	else
-		result = dbentry->n_temp_files;
+		result = dbentry->counts.n_temp_files;
 
 	PG_RETURN_INT64(result);
 }
@@ -1437,7 +1434,7 @@ pg_stat_get_db_temp_bytes(PG_FUNCTION_ARGS)
 	if ((dbentry = pgstat_fetch_stat_dbentry(dbid)) == NULL)
 		result = 0;
 	else
-		result = dbentry->n_temp_bytes;
+		result = dbentry->counts.n_temp_bytes;
 
 	PG_RETURN_INT64(result);
 }
@@ -1452,7 +1449,7 @@ pg_stat_get_db_conflict_tablespace(PG_FUNCTION_ARGS)
 	if ((dbentry = pgstat_fetch_stat_dbentry(dbid)) == NULL)
 		result = 0;
 	else
-		result = (int64) (dbentry->n_conflict_tablespace);
+		result = (int64) (dbentry->counts.n_conflict_tablespace);
 
 	PG_RETURN_INT64(result);
 }
@@ -1467,7 +1464,7 @@ pg_stat_get_db_conflict_lock(PG_FUNCTION_ARGS)
 	if ((dbentry = pgstat_fetch_stat_dbentry(dbid)) == NULL)
 		result = 0;
 	else
-		result = (int64) (dbentry->n_conflict_lock);
+		result = (int64) (dbentry->counts.n_conflict_lock);
 
 	PG_RETURN_INT64(result);
 }
@@ -1482,7 +1479,7 @@ pg_stat_get_db_conflict_snapshot(PG_FUNCTION_ARGS)
 	if ((dbentry = pgstat_fetch_stat_dbentry(dbid)) == NULL)
 		result = 0;
 	else
-		result = (int64) (dbentry->n_conflict_snapshot);
+		result = (int64) (dbentry->counts.n_conflict_snapshot);
 
 	PG_RETURN_INT64(result);
 }
@@ -1497,7 +1494,7 @@ pg_stat_get_db_conflict_bufferpin(PG_FUNCTION_ARGS)
 	if ((dbentry = pgstat_fetch_stat_dbentry(dbid)) == NULL)
 		result = 0;
 	else
-		result = (int64) (dbentry->n_conflict_bufferpin);
+		result = (int64) (dbentry->counts.n_conflict_bufferpin);
 
 	PG_RETURN_INT64(result);
 }
@@ -1512,7 +1509,7 @@ pg_stat_get_db_conflict_startup_deadlock(PG_FUNCTION_ARGS)
 	if ((dbentry = pgstat_fetch_stat_dbentry(dbid)) == NULL)
 		result = 0;
 	else
-		result = (int64) (dbentry->n_conflict_startup_deadlock);
+		result = (int64) (dbentry->counts.n_conflict_startup_deadlock);
 
 	PG_RETURN_INT64(result);
 }
@@ -1527,11 +1524,11 @@ pg_stat_get_db_conflict_all(PG_FUNCTION_ARGS)
 	if ((dbentry = pgstat_fetch_stat_dbentry(dbid)) == NULL)
 		result = 0;
 	else
-		result = (int64) (dbentry->n_conflict_tablespace +
-						  dbentry->n_conflict_lock +
-						  dbentry->n_conflict_snapshot +
-						  dbentry->n_conflict_bufferpin +
-						  dbentry->n_conflict_startup_deadlock);
+		result = (int64) (dbentry->counts.n_conflict_tablespace +
+						  dbentry->counts.n_conflict_lock +
+						  dbentry->counts.n_conflict_snapshot +
+						  dbentry->counts.n_conflict_bufferpin +
+						  dbentry->counts.n_conflict_startup_deadlock);
 
 	PG_RETURN_INT64(result);
 }
@@ -1546,7 +1543,7 @@ pg_stat_get_db_deadlocks(PG_FUNCTION_ARGS)
 	if ((dbentry = pgstat_fetch_stat_dbentry(dbid)) == NULL)
 		result = 0;
 	else
-		result = (int64) (dbentry->n_deadlocks);
+		result = (int64) (dbentry->counts.n_deadlocks);
 
 	PG_RETURN_INT64(result);
 }
@@ -1564,7 +1561,7 @@ pg_stat_get_db_checksum_failures(PG_FUNCTION_ARGS)
 	if ((dbentry = pgstat_fetch_stat_dbentry(dbid)) == NULL)
 		result = 0;
 	else
-		result = (int64) (dbentry->n_checksum_failures);
+		result = (int64) (dbentry->counts.n_checksum_failures);
 
 	PG_RETURN_INT64(result);
 }
@@ -1601,7 +1598,7 @@ pg_stat_get_db_blk_read_time(PG_FUNCTION_ARGS)
 	if ((dbentry = pgstat_fetch_stat_dbentry(dbid)) == NULL)
 		result = 0;
 	else
-		result = ((double) dbentry->n_block_read_time) / 1000.0;
+		result = ((double) dbentry->counts.n_block_read_time) / 1000.0;
 
 	PG_RETURN_FLOAT8(result);
 }
@@ -1617,7 +1614,7 @@ pg_stat_get_db_blk_write_time(PG_FUNCTION_ARGS)
 	if ((dbentry = pgstat_fetch_stat_dbentry(dbid)) == NULL)
 		result = 0;
 	else
-		result = ((double) dbentry->n_block_write_time) / 1000.0;
+		result = ((double) dbentry->counts.n_block_write_time) / 1000.0;
 
 	PG_RETURN_FLOAT8(result);
 }
diff --git a/src/backend/utils/init/globals.c b/src/backend/utils/init/globals.c
index eb19644419..51748c99ad 100644
--- a/src/backend/utils/init/globals.c
+++ b/src/backend/utils/init/globals.c
@@ -33,6 +33,7 @@ volatile sig_atomic_t ProcDiePending = false;
 volatile sig_atomic_t ClientConnectionLost = false;
 volatile sig_atomic_t IdleInTransactionSessionTimeoutPending = false;
 volatile sig_atomic_t ProcSignalBarrierPending = false;
+volatile sig_atomic_t IdleStatsUpdateTimeoutPending = false;
 volatile uint32 InterruptHoldoffCount = 0;
 volatile uint32 QueryCancelHoldoffCount = 0;
 volatile uint32 CritSectionCount = 0;
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index f4247ea70d..f65d05c24c 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -73,6 +73,7 @@ static void ShutdownPostgres(int code, Datum arg);
 static void StatementTimeoutHandler(void);
 static void LockTimeoutHandler(void);
 static void IdleInTransactionSessionTimeoutHandler(void);
+static void IdleStatsUpdateTimeoutHandler(void);
 static bool ThereIsAtLeastOneRole(void);
 static void process_startup_options(Port *port, bool am_superuser);
 static void process_settings(Oid databaseid, Oid roleid);
@@ -631,6 +632,8 @@ InitPostgres(const char *in_dbname, Oid dboid, const char *username,
 		RegisterTimeout(LOCK_TIMEOUT, LockTimeoutHandler);
 		RegisterTimeout(IDLE_IN_TRANSACTION_SESSION_TIMEOUT,
 						IdleInTransactionSessionTimeoutHandler);
+		RegisterTimeout(IDLE_STATS_UPDATE_TIMEOUT,
+						IdleStatsUpdateTimeoutHandler);
 	}
 
 	/*
@@ -1241,6 +1244,14 @@ IdleInTransactionSessionTimeoutHandler(void)
 	SetLatch(MyLatch);
 }
 
+static void
+IdleStatsUpdateTimeoutHandler(void)
+{
+	IdleStatsUpdateTimeoutPending = true;
+	InterruptPending = true;
+	SetLatch(MyLatch);
+}
+
 /*
  * Returns true if at least one role is defined in this database cluster.
  */
diff --git a/src/bin/pg_basebackup/t/010_pg_basebackup.pl b/src/bin/pg_basebackup/t/010_pg_basebackup.pl
index 3c70499feb..927ae319b1 100644
--- a/src/bin/pg_basebackup/t/010_pg_basebackup.pl
+++ b/src/bin/pg_basebackup/t/010_pg_basebackup.pl
@@ -6,7 +6,7 @@ use File::Basename qw(basename dirname);
 use File::Path qw(rmtree);
 use PostgresNode;
 use TestLib;
-use Test::More tests => 107;
+use Test::More tests => 106;
 
 program_help_ok('pg_basebackup');
 program_version_ok('pg_basebackup');
@@ -123,7 +123,7 @@ is_deeply(
 
 # Contents of these directories should not be copied.
 foreach my $dirname (
-	qw(pg_dynshmem pg_notify pg_replslot pg_serial pg_snapshots pg_stat_tmp pg_subtrans)
+	qw(pg_dynshmem pg_notify pg_replslot pg_serial pg_snapshots pg_subtrans)
   )
 {
 	is_deeply(
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 619b2f9c71..9f1de1e42f 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -83,6 +83,8 @@ extern PGDLLIMPORT volatile sig_atomic_t QueryCancelPending;
 extern PGDLLIMPORT volatile sig_atomic_t ProcDiePending;
 extern PGDLLIMPORT volatile sig_atomic_t IdleInTransactionSessionTimeoutPending;
 extern PGDLLIMPORT volatile sig_atomic_t ProcSignalBarrierPending;
+extern PGDLLIMPORT volatile sig_atomic_t IdleStatsUpdateTimeoutPending;
+extern PGDLLIMPORT volatile sig_atomic_t ConfigReloadPending;
 
 extern PGDLLIMPORT volatile sig_atomic_t ClientConnectionLost;
 
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index 763c1ee2bd..69bd794806 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -1,7 +1,7 @@
 /* ----------
  *	pgstat.h
  *
- *	Definitions for the PostgreSQL statistics collector daemon.
+ *	Definitions for the PostgreSQL activity statistics facility.
  *
  *	Copyright (c) 2001-2020, PostgreSQL Global Development Group
  *
@@ -15,9 +15,11 @@
 #include "libpq/pqcomm.h"
 #include "miscadmin.h"
 #include "port/atomics.h"
+#include "lib/dshash.h"
 #include "portability/instr_time.h"
 #include "postmaster/pgarch.h"
 #include "storage/proc.h"
+#include "storage/lwlock.h"
 #include "utils/hsearch.h"
 #include "utils/relcache.h"
 
@@ -41,33 +43,6 @@ typedef enum TrackFunctionsLevel
 	TRACK_FUNC_ALL
 }			TrackFunctionsLevel;
 
-/* ----------
- * The types of backend -> collector messages
- * ----------
- */
-typedef enum StatMsgType
-{
-	PGSTAT_MTYPE_DUMMY,
-	PGSTAT_MTYPE_INQUIRY,
-	PGSTAT_MTYPE_TABSTAT,
-	PGSTAT_MTYPE_TABPURGE,
-	PGSTAT_MTYPE_DROPDB,
-	PGSTAT_MTYPE_RESETCOUNTER,
-	PGSTAT_MTYPE_RESETSHAREDCOUNTER,
-	PGSTAT_MTYPE_RESETSINGLECOUNTER,
-	PGSTAT_MTYPE_AUTOVAC_START,
-	PGSTAT_MTYPE_VACUUM,
-	PGSTAT_MTYPE_ANALYZE,
-	PGSTAT_MTYPE_ARCHIVER,
-	PGSTAT_MTYPE_BGWRITER,
-	PGSTAT_MTYPE_FUNCSTAT,
-	PGSTAT_MTYPE_FUNCPURGE,
-	PGSTAT_MTYPE_RECOVERYCONFLICT,
-	PGSTAT_MTYPE_TEMPFILE,
-	PGSTAT_MTYPE_DEADLOCK,
-	PGSTAT_MTYPE_CHECKSUMFAILURE
-} StatMsgType;
-
 /* ----------
  * The data type used for counters.
  * ----------
@@ -78,9 +53,8 @@ typedef int64 PgStat_Counter;
  * PgStat_TableCounts			The actual per-table counts kept by a backend
  *
  * This struct should contain only actual event counters, because we memcmp
- * it against zeroes to detect whether there are any counts to transmit.
- * It is a component of PgStat_TableStatus (within-backend state) and
- * PgStat_TableEntry (the transmitted message format).
+ * it against zeroes to detect whether there are any counts to write.
+ * It is a component of PgStat_TableStatus (within-backend state).
  *
  * Note: for a table, tuples_returned is the number of tuples successfully
  * fetched by heap_getnext, while tuples_fetched is the number of tuples
@@ -111,18 +85,17 @@ typedef struct PgStat_TableCounts
 	PgStat_Counter t_delta_live_tuples;
 	PgStat_Counter t_delta_dead_tuples;
 	PgStat_Counter t_changed_tuples;
+	bool		reset_changed_tuples;
 
 	PgStat_Counter t_blocks_fetched;
 	PgStat_Counter t_blocks_hit;
+
+	PgStat_Counter vacuum_count;
+	PgStat_Counter autovac_vacuum_count;
+	PgStat_Counter analyze_count;
+	PgStat_Counter autovac_analyze_count;
 } PgStat_TableCounts;
 
-/* Possible targets for resetting cluster-wide shared values */
-typedef enum PgStat_Shared_Reset_Target
-{
-	RESET_ARCHIVER,
-	RESET_BGWRITER
-} PgStat_Shared_Reset_Target;
-
 /* Possible object types for resetting single counters */
 typedef enum PgStat_Single_Reset_Type
 {
@@ -156,6 +129,10 @@ typedef struct PgStat_TableStatus
 	Oid			t_id;			/* table's OID */
 	bool		t_shared;		/* is it a shared catalog? */
 	struct PgStat_TableXactStatus *trans;	/* lowest subxact's counts */
+	TimestampTz vacuum_timestamp;	/* user initiated vacuum */
+	TimestampTz autovac_vacuum_timestamp;	/* autovacuum initiated */
+	TimestampTz analyze_timestamp;	/* user initiated */
+	TimestampTz autovac_analyze_timestamp;	/* autovacuum initiated */
 	PgStat_TableCounts t_counts;	/* event counts to be sent */
 } PgStat_TableStatus;
 
@@ -181,280 +158,32 @@ typedef struct PgStat_TableXactStatus
 } PgStat_TableXactStatus;

-/* ------------------------------------------------------------
- * Message formats follow
- * ------------------------------------------------------------
- */
-
-
-/* ----------
- * PgStat_MsgHdr				The common message header
- * ----------
- */
-typedef struct PgStat_MsgHdr
-{
-	StatMsgType m_type;
-	int			m_size;
-} PgStat_MsgHdr;
-
-/* ----------
- * Space available in a message.  This will keep the UDP packets below 1K,
- * which should fit unfragmented into the MTU of the loopback interface.
- * (Larger values of PGSTAT_MAX_MSG_SIZE would work for that on most
- * platforms, but we're being conservative here.)
- * ----------
- */
-#define PGSTAT_MAX_MSG_SIZE 1000
-#define PGSTAT_MSG_PAYLOAD	(PGSTAT_MAX_MSG_SIZE - sizeof(PgStat_MsgHdr))
-
-
-/* ----------
- * PgStat_MsgDummy				A dummy message, ignored by the collector
- * ----------
- */
-typedef struct PgStat_MsgDummy
-{
-	PgStat_MsgHdr m_hdr;
-} PgStat_MsgDummy;
-
-
-/* ----------
- * PgStat_MsgInquiry			Sent by a backend to ask the collector
- *								to write the stats file(s).
- *
- * Ordinarily, an inquiry message prompts writing of the global stats file,
- * the stats file for shared catalogs, and the stats file for the specified
- * database.  If databaseid is InvalidOid, only the first two are written.
- *
- * New file(s) will be written only if the existing file has a timestamp
- * older than the specified cutoff_time; this prevents duplicated effort
- * when multiple requests arrive at nearly the same time, assuming that
- * backends send requests with cutoff_times a little bit in the past.
- *
- * clock_time should be the requestor's current local time; the collector
- * uses this to check for the system clock going backward, but it has no
- * effect unless that occurs.  We assume clock_time >= cutoff_time, though.
- * ----------
- */
-
-typedef struct PgStat_MsgInquiry
-{
-	PgStat_MsgHdr m_hdr;
-	TimestampTz clock_time;		/* observed local clock time */
-	TimestampTz cutoff_time;	/* minimum acceptable file timestamp */
-	Oid			databaseid;		/* requested DB (InvalidOid => shared only) */
-} PgStat_MsgInquiry;
-
-
-/* ----------
- * PgStat_TableEntry			Per-table info in a MsgTabstat
- * ----------
- */
-typedef struct PgStat_TableEntry
-{
-	Oid			t_id;
-	PgStat_TableCounts t_counts;
-} PgStat_TableEntry;
-
-/* ----------
- * PgStat_MsgTabstat			Sent by the backend to report table
- *								and buffer access statistics.
- * ----------
- */
-#define PGSTAT_NUM_TABENTRIES  \
-	((PGSTAT_MSG_PAYLOAD - sizeof(Oid) - 3 * sizeof(int) - 2 * sizeof(PgStat_Counter))	\
-	 / sizeof(PgStat_TableEntry))
-
-typedef struct PgStat_MsgTabstat
-{
-	PgStat_MsgHdr m_hdr;
-	Oid			m_databaseid;
-	int			m_nentries;
-	int			m_xact_commit;
-	int			m_xact_rollback;
-	PgStat_Counter m_block_read_time;	/* times in microseconds */
-	PgStat_Counter m_block_write_time;
-	PgStat_TableEntry m_entry[PGSTAT_NUM_TABENTRIES];
-} PgStat_MsgTabstat;
-
-
-/* ----------
- * PgStat_MsgTabpurge			Sent by the backend to tell the collector
- *								about dead tables.
- * ----------
- */
-#define PGSTAT_NUM_TABPURGE  \
-	((PGSTAT_MSG_PAYLOAD - sizeof(Oid) - sizeof(int))  \
-	 / sizeof(Oid))
-
-typedef struct PgStat_MsgTabpurge
-{
-	PgStat_MsgHdr m_hdr;
-	Oid			m_databaseid;
-	int			m_nentries;
-	Oid			m_tableid[PGSTAT_NUM_TABPURGE];
-} PgStat_MsgTabpurge;
-
-
-/* ----------
- * PgStat_MsgDropdb				Sent by the backend to tell the collector
- *								about a dropped database
- * ----------
- */
-typedef struct PgStat_MsgDropdb
-{
-	PgStat_MsgHdr m_hdr;
-	Oid			m_databaseid;
-} PgStat_MsgDropdb;
-
-
-/* ----------
- * PgStat_MsgResetcounter		Sent by the backend to tell the collector
- *								to reset counters
- * ----------
- */
-typedef struct PgStat_MsgResetcounter
-{
-	PgStat_MsgHdr m_hdr;
-	Oid			m_databaseid;
-} PgStat_MsgResetcounter;
-
-/* ----------
- * PgStat_MsgResetsharedcounter Sent by the backend to tell the collector
- *								to reset a shared counter
- * ----------
- */
-typedef struct PgStat_MsgResetsharedcounter
-{
-	PgStat_MsgHdr m_hdr;
-	PgStat_Shared_Reset_Target m_resettarget;
-} PgStat_MsgResetsharedcounter;
-
-/* ----------
- * PgStat_MsgResetsinglecounter Sent by the backend to tell the collector
- *								to reset a single counter
- * ----------
- */
-typedef struct PgStat_MsgResetsinglecounter
-{
-	PgStat_MsgHdr m_hdr;
-	Oid			m_databaseid;
-	PgStat_Single_Reset_Type m_resettype;
-	Oid			m_objectid;
-} PgStat_MsgResetsinglecounter;
-
-/* ----------
- * PgStat_MsgAutovacStart		Sent by the autovacuum daemon to signal
- *								that a database is going to be processed
- * ----------
- */
-typedef struct PgStat_MsgAutovacStart
-{
-	PgStat_MsgHdr m_hdr;
-	Oid			m_databaseid;
-	TimestampTz m_start_time;
-} PgStat_MsgAutovacStart;
-
-
-/* ----------
- * PgStat_MsgVacuum				Sent by the backend or autovacuum daemon
- *								after VACUUM
- * ----------
- */
-typedef struct PgStat_MsgVacuum
-{
-	PgStat_MsgHdr m_hdr;
-	Oid			m_databaseid;
-	Oid			m_tableoid;
-	bool		m_autovacuum;
-	TimestampTz m_vacuumtime;
-	PgStat_Counter m_live_tuples;
-	PgStat_Counter m_dead_tuples;
-} PgStat_MsgVacuum;
-
-
-/* ----------
- * PgStat_MsgAnalyze			Sent by the backend or autovacuum daemon
- *								after ANALYZE
- * ----------
- */
-typedef struct PgStat_MsgAnalyze
-{
-	PgStat_MsgHdr m_hdr;
-	Oid			m_databaseid;
-	Oid			m_tableoid;
-	bool		m_autovacuum;
-	bool		m_resetcounter;
-	TimestampTz m_analyzetime;
-	PgStat_Counter m_live_tuples;
-	PgStat_Counter m_dead_tuples;
-} PgStat_MsgAnalyze;
-
-
-/* ----------
- * PgStat_MsgArchiver			Sent by the archiver to update statistics.
- * ----------
- */
-typedef struct PgStat_MsgArchiver
-{
-	PgStat_MsgHdr m_hdr;
-	bool		m_failed;		/* Failed attempt */
-	char		m_xlog[MAX_XFN_CHARS + 1];
-	TimestampTz m_timestamp;
-} PgStat_MsgArchiver;
-
-/* ----------
- * PgStat_MsgBgWriter			Sent by the bgwriter to update statistics.
- * ----------
- */
-typedef struct PgStat_MsgBgWriter
-{
-	PgStat_MsgHdr m_hdr;
-
-	PgStat_Counter m_timed_checkpoints;
-	PgStat_Counter m_requested_checkpoints;
-	PgStat_Counter m_buf_written_checkpoints;
-	PgStat_Counter m_buf_written_clean;
-	PgStat_Counter m_maxwritten_clean;
-	PgStat_Counter m_buf_written_backend;
-	PgStat_Counter m_buf_fsync_backend;
-	PgStat_Counter m_buf_alloc;
-	PgStat_Counter m_checkpoint_write_time; /* times in milliseconds */
-	PgStat_Counter m_checkpoint_sync_time;
-} PgStat_MsgBgWriter;
-
-/* ----------
- * PgStat_MsgRecoveryConflict	Sent by the backend upon recovery conflict
- * ----------
- */
-typedef struct PgStat_MsgRecoveryConflict
-{
-	PgStat_MsgHdr m_hdr;
-
-	Oid			m_databaseid;
-	int			m_reason;
-} PgStat_MsgRecoveryConflict;
-
 /* ----------
- * PgStat_MsgTempFile	Sent by the backend upon creating a temp file
+ * PgStat_BgWriter			bgwriter statistics
  * ----------
  */
-typedef struct PgStat_MsgTempFile
+typedef struct PgStat_BgWriter
 {
-	PgStat_MsgHdr m_hdr;
-
-	Oid			m_databaseid;
-	size_t		m_filesize;
-} PgStat_MsgTempFile;
+	PgStat_Counter timed_checkpoints;
+	PgStat_Counter requested_checkpoints;
+	PgStat_Counter buf_written_checkpoints;
+	PgStat_Counter buf_written_clean;
+	PgStat_Counter maxwritten_clean;
+	PgStat_Counter buf_written_backend;
+	PgStat_Counter buf_fsync_backend;
+	PgStat_Counter buf_alloc;
+	PgStat_Counter checkpoint_write_time;	/* times in milliseconds */
+	PgStat_Counter checkpoint_sync_time;
+}			PgStat_BgWriter;
 
 /* ----------
  * PgStat_FunctionCounts	The actual per-function counts kept by a backend
  *
  * This struct should contain only actual event counters, because we memcmp
- * it against zeroes to detect whether there are any counts to transmit.
+ * it against zeroes to detect whether there are any counts to write.
  *
  * Note that the time counters are in instr_time format here.  We convert to
- * microseconds in PgStat_Counter format when transmitting to the collector.
+ * microseconds in PgStat_Counter format when writing to shared statsitics.
  * ----------
  */
 typedef struct PgStat_FunctionCounts
@@ -486,96 +215,8 @@ typedef struct PgStat_FunctionEntry
 	PgStat_Counter f_self_time;
 } PgStat_FunctionEntry;
 
-/* ----------
- * PgStat_MsgFuncstat			Sent by the backend to report function
- *								usage statistics.
- * ----------
- */
-#define PGSTAT_NUM_FUNCENTRIES	\
-	((PGSTAT_MSG_PAYLOAD - sizeof(Oid) - sizeof(int))  \
-	 / sizeof(PgStat_FunctionEntry))
-
-typedef struct PgStat_MsgFuncstat
-{
-	PgStat_MsgHdr m_hdr;
-	Oid			m_databaseid;
-	int			m_nentries;
-	PgStat_FunctionEntry m_entry[PGSTAT_NUM_FUNCENTRIES];
-} PgStat_MsgFuncstat;
-
-/* ----------
- * PgStat_MsgFuncpurge			Sent by the backend to tell the collector
- *								about dead functions.
- * ----------
- */
-#define PGSTAT_NUM_FUNCPURGE  \
-	((PGSTAT_MSG_PAYLOAD - sizeof(Oid) - sizeof(int))  \
-	 / sizeof(Oid))
-
-typedef struct PgStat_MsgFuncpurge
-{
-	PgStat_MsgHdr m_hdr;
-	Oid			m_databaseid;
-	int			m_nentries;
-	Oid			m_functionid[PGSTAT_NUM_FUNCPURGE];
-} PgStat_MsgFuncpurge;
-
-/* ----------
- * PgStat_MsgDeadlock			Sent by the backend to tell the collector
- *								about a deadlock that occurred.
- * ----------
- */
-typedef struct PgStat_MsgDeadlock
-{
-	PgStat_MsgHdr m_hdr;
-	Oid			m_databaseid;
-} PgStat_MsgDeadlock;
-
-/* ----------
- * PgStat_MsgChecksumFailure	Sent by the backend to tell the collector
- *								about checksum failures noticed.
- * ----------
- */
-typedef struct PgStat_MsgChecksumFailure
-{
-	PgStat_MsgHdr m_hdr;
-	Oid			m_databaseid;
-	int			m_failurecount;
-	TimestampTz m_failure_time;
-} PgStat_MsgChecksumFailure;
-
-
-/* ----------
- * PgStat_Msg					Union over all possible messages.
- * ----------
- */
-typedef union PgStat_Msg
-{
-	PgStat_MsgHdr msg_hdr;
-	PgStat_MsgDummy msg_dummy;
-	PgStat_MsgInquiry msg_inquiry;
-	PgStat_MsgTabstat msg_tabstat;
-	PgStat_MsgTabpurge msg_tabpurge;
-	PgStat_MsgDropdb msg_dropdb;
-	PgStat_MsgResetcounter msg_resetcounter;
-	PgStat_MsgResetsharedcounter msg_resetsharedcounter;
-	PgStat_MsgResetsinglecounter msg_resetsinglecounter;
-	PgStat_MsgAutovacStart msg_autovacuum_start;
-	PgStat_MsgVacuum msg_vacuum;
-	PgStat_MsgAnalyze msg_analyze;
-	PgStat_MsgArchiver msg_archiver;
-	PgStat_MsgBgWriter msg_bgwriter;
-	PgStat_MsgFuncstat msg_funcstat;
-	PgStat_MsgFuncpurge msg_funcpurge;
-	PgStat_MsgRecoveryConflict msg_recoveryconflict;
-	PgStat_MsgDeadlock msg_deadlock;
-	PgStat_MsgTempFile msg_tempfile;
-	PgStat_MsgChecksumFailure msg_checksumfailure;
-} PgStat_Msg;
-
-
 /* ------------------------------------------------------------
- * Statistic collector data structures follow
+ * Activity statistics data structures on file and shared memory follow
  *
  * PGSTAT_FILE_FORMAT_ID should be changed whenever any of these
  * data structures change.
@@ -584,13 +225,9 @@ typedef union PgStat_Msg
 
 #define PGSTAT_FILE_FORMAT_ID	0x01A5BC9D
 
-/* ----------
- * PgStat_StatDBEntry			The collector's data per database
- * ----------
- */
-typedef struct PgStat_StatDBEntry
+
+typedef struct PgStat_StatDBCounts
 {
-	Oid			databaseid;
 	PgStat_Counter n_xact_commit;
 	PgStat_Counter n_xact_rollback;
 	PgStat_Counter n_blocks_fetched;
@@ -600,7 +237,6 @@ typedef struct PgStat_StatDBEntry
 	PgStat_Counter n_tuples_inserted;
 	PgStat_Counter n_tuples_updated;
 	PgStat_Counter n_tuples_deleted;
-	TimestampTz last_autovac_time;
 	PgStat_Counter n_conflict_tablespace;
 	PgStat_Counter n_conflict_lock;
 	PgStat_Counter n_conflict_snapshot;
@@ -610,29 +246,55 @@ typedef struct PgStat_StatDBEntry
 	PgStat_Counter n_temp_bytes;
 	PgStat_Counter n_deadlocks;
 	PgStat_Counter n_checksum_failures;
-	TimestampTz last_checksum_failure;
 	PgStat_Counter n_block_read_time;	/* times in microseconds */
 	PgStat_Counter n_block_write_time;
+} PgStat_StatDBCounts;
 
+/* ----------
+ * PgStat_StatDBEntry			The statistics per database
+ * ----------
+ */
+typedef struct PgStat_StatDBEntry
+{
+	Oid			databaseid;
+	TimestampTz last_autovac_time;
+	TimestampTz last_checksum_failure;
 	TimestampTz stat_reset_timestamp;
-	TimestampTz stats_timestamp;	/* time of db stats file update */
+	TimestampTz stats_timestamp;	/* time of db stats update */
+
+	PgStat_StatDBCounts counts;
 
 	/*
-	 * tables and functions must be last in the struct, because we don't write
-	 * the pointers out to the stats file.
+	 * The followings must be last in the struct, because we don't write them
+	 * out to the stats file.
 	 */
-	HTAB	   *tables;
-	HTAB	   *functions;
+	dshash_table_handle tables; /* current gen tables hash */
+	dshash_table_handle functions;	/* current gen functions hash */
 } PgStat_StatDBEntry;
 
+/* ----------
+ * PgStat_HashMountInfo  dshash mount information
+ * ----------
+ */
+typedef struct PgStat_HashMountInfo
+{
+	HTAB	   *snapshot_tables;	/* table entry snapshot */
+	HTAB	   *snapshot_functions; /* function entry snapshot */
+	dshash_table *dshash_tables;	/* attached tables dshash */
+	dshash_table *dshash_functions; /* attached functions dshash */
+} PgStat_HashMountInfo;
 
 /* ----------
- * PgStat_StatTabEntry			The collector's data per table (or index)
+ * PgStat_StatTabEntry			The statistics per table (or index)
  * ----------
  */
 typedef struct PgStat_StatTabEntry
 {
 	Oid			tableid;
+	TimestampTz vacuum_timestamp;	/* user initiated vacuum */
+	TimestampTz autovac_vacuum_timestamp;	/* autovacuum initiated */
+	TimestampTz analyze_timestamp;	/* user initiated */
+	TimestampTz autovac_analyze_timestamp;	/* autovacuum initiated */
 
 	PgStat_Counter numscans;
 
@@ -652,19 +314,15 @@ typedef struct PgStat_StatTabEntry
 	PgStat_Counter blocks_fetched;
 	PgStat_Counter blocks_hit;
 
-	TimestampTz vacuum_timestamp;	/* user initiated vacuum */
 	PgStat_Counter vacuum_count;
-	TimestampTz autovac_vacuum_timestamp;	/* autovacuum initiated */
 	PgStat_Counter autovac_vacuum_count;
-	TimestampTz analyze_timestamp;	/* user initiated */
 	PgStat_Counter analyze_count;
-	TimestampTz autovac_analyze_timestamp;	/* autovacuum initiated */
 	PgStat_Counter autovac_analyze_count;
 } PgStat_StatTabEntry;

 /* ----------
- * PgStat_StatFuncEntry			The collector's data per function
+ * PgStat_StatFuncEntry			per function stats data
  * ----------
  */
 typedef struct PgStat_StatFuncEntry
@@ -679,7 +337,7 @@ typedef struct PgStat_StatFuncEntry

 /*
- * Archiver statistics kept in the stats collector
+ * Archiver statistics kept in the shared stats
  */
 typedef struct PgStat_ArchiverStats
 {
@@ -695,7 +353,7 @@ typedef struct PgStat_ArchiverStats
 } PgStat_ArchiverStats;
 
 /*
- * Global statistics kept in the stats collector
+ * Global statistics kept in the shared stats
  */
 typedef struct PgStat_GlobalStats
 {
@@ -761,7 +419,6 @@ typedef enum
 	WAIT_EVENT_CHECKPOINTER_MAIN,
 	WAIT_EVENT_LOGICAL_APPLY_MAIN,
 	WAIT_EVENT_LOGICAL_LAUNCHER_MAIN,
-	WAIT_EVENT_PGSTAT_MAIN,
 	WAIT_EVENT_RECOVERY_WAL_STREAM,
 	WAIT_EVENT_SYSLOGGER_MAIN,
 	WAIT_EVENT_WAL_RECEIVER_MAIN,
@@ -1005,7 +662,7 @@ typedef struct PgBackendGSSStatus
  *
  * Each live backend maintains a PgBackendStatus struct in shared memory
  * showing its current activity.  (The structs are allocated according to
- * BackendId, but that is not critical.)  Note that the collector process
+ * BackendId, but that is not critical.)  Note that the stats-writing functions
  * has no involvement in, or even access to, these structs.
  *
  * Each auxiliary process also maintains a PgBackendStatus struct in shared
@@ -1202,13 +859,15 @@ extern PGDLLIMPORT bool pgstat_track_counts;
 extern PGDLLIMPORT int pgstat_track_functions;
 extern PGDLLIMPORT int pgstat_track_activity_query_size;
 extern char *pgstat_stat_directory;
+
+/* No longer used, but will be removed with GUC */
 extern char *pgstat_stat_tmpname;
 extern char *pgstat_stat_filename;
 
 /*
  * BgWriter statistics counters are updated directly by bgwriter and bufmgr
  */
-extern PgStat_MsgBgWriter BgWriterStats;
+extern PgStat_BgWriter BgWriterStats;
 
 /*
  * Updated by pgstat_count_buffer_*_time macros
@@ -1223,29 +882,26 @@ extern PgStat_Counter pgStatBlockWriteTime;
 extern Size BackendStatusShmemSize(void);
 extern void CreateSharedBackendStatus(void);
 
-extern void pgstat_init(void);
-extern int	pgstat_start(void);
+extern Size StatsShmemSize(void);
+extern void StatsShmemInit(void);
+
 extern void pgstat_reset_all(void);
-extern void allow_immediate_pgstat_restart(void);
-
-#ifdef EXEC_BACKEND
-extern void PgstatCollectorMain(int argc, char *argv[]) pg_attribute_noreturn();
-#endif
 
+/* File input/output functions  */
+extern void pgstat_read_statsfiles(void);
+extern void pgstat_write_statsfiles(void);
 
 /* ----------
  * Functions called from backends
  * ----------
  */
-extern void pgstat_ping(void);
-
-extern void pgstat_report_stat(bool force);
+extern long pgstat_report_stat(bool force);
 extern void pgstat_vacuum_stat(void);
 extern void pgstat_drop_database(Oid databaseid);
 
 extern void pgstat_clear_snapshot(void);
 extern void pgstat_reset_counters(void);
-extern void pgstat_reset_shared_counters(const char *);
+extern void pgstat_reset_shared_counters(const char *target);
 extern void pgstat_reset_single_counter(Oid objectid, PgStat_Single_Reset_Type type);
 
 extern void pgstat_report_autovac(Oid dboid);
@@ -1406,8 +1062,8 @@ extern void pgstat_twophase_postcommit(TransactionId xid, uint16 info,
 extern void pgstat_twophase_postabort(TransactionId xid, uint16 info,
 									  void *recdata, uint32 len);
 
-extern void pgstat_send_archiver(const char *xlog, bool failed);
-extern void pgstat_send_bgwriter(void);
+extern void pgstat_report_archiver(const char *xlog, bool failed);
+extern void pgstat_report_bgwriter(void);
 
 /* ----------
  * Support functions for the SQL-callable functions to
@@ -1416,11 +1072,15 @@ extern void pgstat_send_bgwriter(void);
  */
 extern PgStat_StatDBEntry *pgstat_fetch_stat_dbentry(Oid dbid);
 extern PgStat_StatTabEntry *pgstat_fetch_stat_tabentry(Oid relid);
+extern PgStat_StatTabEntry *pgstat_fetch_stat_tabentry_snapshot(bool shared,
+																Oid relid);
+extern void pgstat_copy_index_counters(Oid relid, PgStat_TableStatus *dst);
 extern PgBackendStatus *pgstat_fetch_stat_beentry(int beid);
 extern LocalPgBackendStatus *pgstat_fetch_stat_local_beentry(int beid);
 extern PgStat_StatFuncEntry *pgstat_fetch_stat_funcentry(Oid funcid);
 extern int	pgstat_fetch_stat_numbackends(void);
 extern PgStat_ArchiverStats *pgstat_fetch_stat_archiver(void);
 extern PgStat_GlobalStats *pgstat_fetch_global(void);
+extern void pgstat_clear_snapshot(void);
 
 #endif							/* PGSTAT_H */
diff --git a/src/include/storage/lwlock.h b/src/include/storage/lwlock.h
index 8fda8e4f78..13371e8cb7 100644
--- a/src/include/storage/lwlock.h
+++ b/src/include/storage/lwlock.h
@@ -220,6 +220,7 @@ typedef enum BuiltinTrancheIds
 	LWTRANCHE_TBM,
 	LWTRANCHE_PARALLEL_APPEND,
 	LWTRANCHE_SXACT,
+	LWTRANCHE_STATS,
 	LWTRANCHE_FIRST_USER_DEFINED
 }			BuiltinTrancheIds;
 
diff --git a/src/include/utils/timeout.h b/src/include/utils/timeout.h
index 83a15f6795..77d1572a99 100644
--- a/src/include/utils/timeout.h
+++ b/src/include/utils/timeout.h
@@ -31,6 +31,7 @@ typedef enum TimeoutId
 	STANDBY_TIMEOUT,
 	STANDBY_LOCK_TIMEOUT,
 	IDLE_IN_TRANSACTION_SESSION_TIMEOUT,
+	IDLE_STATS_UPDATE_TIMEOUT,
 	/* First user-definable timeout reason */
 	USER_TIMEOUT,
 	/* Maximum number of timeout reasons */
-- 
2.18.2

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