Extend framework from commit 53be0b1ad to report latch waits.

WaitLatch, WaitLatchOrSocket, and WaitEventSetWait now taken an
additional wait_event_info parameter; legal values are defined in
pgstat.h.  This makes it possible to uniquely identify every point in
the core code where we are waiting for a latch; extensions can pass
WAIT_EXTENSION.

Because latches were the major wait primitive not previously covered
by this patch, it is now possible to see information in
pg_stat_activity on a large number of important wait events not
previously addressed, such as ClientRead, ClientWrite, and SyncRep.

Unfortunately, many of the wait events added by this patch will fail
to appear in pg_stat_activity because they're only used in background
processes which don't currently appear in pg_stat_activity.  We should
fix this either by creating a separate view for such information, or
else by deciding to include them in pg_stat_activity after all.

Michael Paquier and Robert Haas, reviewed by Alexander Korotkov and
Thomas Munro.

src/backend/storage/ipc/latch.c

@@ -55,6 +55,7 @@
 #endif
 
 #include "miscadmin.h"
+#include "pgstat.h"
 #include "portability/instr_time.h"
 #include "postmaster/postmaster.h"
 #include "storage/barrier.h"
@@ -297,9 +298,11 @@ DisownLatch(volatile Latch *latch)
  * we return all of them in one call, but we will return at least one.
  */
 int
-WaitLatch(volatile Latch *latch, int wakeEvents, long timeout)
+WaitLatch(volatile Latch *latch, int wakeEvents, long timeout,
+		  uint32 wait_event_info)
 {
-	return WaitLatchOrSocket(latch, wakeEvents, PGINVALID_SOCKET, timeout);
+	return WaitLatchOrSocket(latch, wakeEvents, PGINVALID_SOCKET, timeout,
+							 wait_event_info);
 }
 
 /*
@@ -316,7 +319,7 @@ WaitLatch(volatile Latch *latch, int wakeEvents, long timeout)
  */
 int
 WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
-				  long timeout)
+				  long timeout, uint32 wait_event_info)
 {
 	int			ret = 0;
 	int			rc;
@@ -344,7 +347,7 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
 		AddWaitEventToSet(set, ev, sock, NULL, NULL);
 	}
 
-	rc = WaitEventSetWait(set, timeout, &event, 1);
+	rc = WaitEventSetWait(set, timeout, &event, 1, wait_event_info);
 
 	if (rc == 0)
 		ret |= WL_TIMEOUT;
@@ -863,7 +866,8 @@ WaitEventAdjustWin32(WaitEventSet *set, WaitEvent *event)
  */
 int
 WaitEventSetWait(WaitEventSet *set, long timeout,
-				 WaitEvent *occurred_events, int nevents)
+				 WaitEvent *occurred_events, int nevents,
+				 uint32 wait_event_info)
 {
 	int			returned_events = 0;
 	instr_time	start_time;
@@ -883,6 +887,8 @@ WaitEventSetWait(WaitEventSet *set, long timeout,
 		cur_timeout = timeout;
 	}
 
+	pgstat_report_wait_start(wait_event_info);
+
 #ifndef WIN32
 	waiting = true;
 #else
@@ -960,6 +966,8 @@ WaitEventSetWait(WaitEventSet *set, long timeout,
 	waiting = false;
 #endif
 
+	pgstat_report_wait_end();
+
 	return returned_events;
 }
 

src/backend/storage/ipc/shm_mq.c

@@ -19,6 +19,7 @@
 #include "postgres.h"
 
 #include "miscadmin.h"
+#include "pgstat.h"
 #include "postmaster/bgworker.h"
 #include "storage/procsignal.h"
 #include "storage/shm_mq.h"
@@ -894,7 +895,7 @@ shm_mq_send_bytes(shm_mq_handle *mqh, Size nbytes, const void *data,
 			 * at top of loop, because setting an already-set latch is much
 			 * cheaper than setting one that has been reset.
 			 */
-			WaitLatch(MyLatch, WL_LATCH_SET, 0);
+			WaitLatch(MyLatch, WL_LATCH_SET, 0, WAIT_EVENT_MQ_SEND);
 
 			/* Reset the latch so we don't spin. */
 			ResetLatch(MyLatch);
@@ -991,7 +992,7 @@ shm_mq_receive_bytes(shm_mq *mq, Size bytes_needed, bool nowait,
 		 * loop, because setting an already-set latch is much cheaper than
 		 * setting one that has been reset.
 		 */
-		WaitLatch(MyLatch, WL_LATCH_SET, 0);
+		WaitLatch(MyLatch, WL_LATCH_SET, 0, WAIT_EVENT_MQ_RECEIVE);
 
 		/* Reset the latch so we don't spin. */
 		ResetLatch(MyLatch);
@@ -1090,7 +1091,7 @@ shm_mq_wait_internal(volatile shm_mq *mq, PGPROC *volatile * ptr,
 		}
 
 		/* Wait to be signalled. */
-		WaitLatch(MyLatch, WL_LATCH_SET, 0);
+		WaitLatch(MyLatch, WL_LATCH_SET, 0, WAIT_EVENT_MQ_INTERNAL);
 
 		/* Reset the latch so we don't spin. */
 		ResetLatch(MyLatch);

src/backend/storage/ipc/standby.c

@@ -22,6 +22,7 @@
 #include "access/xlog.h"
 #include "access/xloginsert.h"
 #include "miscadmin.h"
+#include "pgstat.h"
 #include "storage/bufmgr.h"
 #include "storage/lmgr.h"
 #include "storage/proc.h"
@@ -389,7 +390,7 @@ ResolveRecoveryConflictWithLock(LOCKTAG locktag)
 	}
 
 	/* Wait to be signaled by the release of the Relation Lock */
-	ProcWaitForSignal();
+	ProcWaitForSignal(WAIT_LOCK | locktag.locktag_type);
 
 	/*
 	 * Clear any timeout requests established above.  We assume here that the
@@ -469,7 +470,7 @@ ResolveRecoveryConflictWithBufferPin(void)
 	}
 
 	/* Wait to be signaled by UnpinBuffer() */
-	ProcWaitForSignal();
+	ProcWaitForSignal(WAIT_BUFFER_PIN);
 
 	/*
 	 * Clear any timeout requests established above.  We assume here that the