Handle impending sinval queue overflow by means of a separate signal

(SIGUSR1, which we have not been using recently) instead of piggybacking
on SIGUSR2-driven NOTIFY processing.  This has several good results:
the processing needed to drain the sinval queue is a lot less than the
processing needed to answer a NOTIFY; there's less contention since we
don't have a bunch of backends all trying to acquire exclusive lock on
pg_listener; backends that are sitting inside a transaction block can
still drain the queue, whereas NOTIFY processing can't run if there's
an open transaction block.  (This last is a fairly serious issue that
I don't think we ever recognized before --- with clients like JDBC that
tend to sit with open transaction blocks, the sinval queue draining
mechanism never really worked as intended, probably resulting in a lot
of useless cache-reset overhead.)  This is the last of several proposed
changes in response to Philip Warner's recent report of sinval-induced
performance problems.

3 files changed, 18 insertions, 10 deletions

diff --git a/src/include/commands/async.h b/src/include/commands/async.h
index bbfb24086e0..6429895fbdc 100644
--- a/src/include/commands/async.h
+++ b/src/include/commands/async.h
@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/commands/async.h,v 1.23 2003/11/29 22:40:59 pgsql Exp $
+ * $PostgreSQL: pgsql/src/include/commands/async.h,v 1.24 2004/05/23 03:50:45 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -25,15 +25,14 @@ extern void AtCommit_Notify(void);
 extern void AtAbort_Notify(void);
 
 /* signal handler for inbound notifies (SIGUSR2) */
-extern void Async_NotifyHandler(SIGNAL_ARGS);
+extern void NotifyInterruptHandler(SIGNAL_ARGS);
 
 /*
  * enable/disable processing of inbound notifies directly from signal handler.
  * The enable routine first performs processing of any inbound notifies that
- * have occurred since the last disable.  These are meant to be called ONLY
- * from the appropriate places in PostgresMain().
+ * have occurred since the last disable.
  */
 extern void EnableNotifyInterrupt(void);
-extern void DisableNotifyInterrupt(void);
+extern bool DisableNotifyInterrupt(void);
 
 #endif   /* ASYNC_H */
diff --git a/src/include/storage/pmsignal.h b/src/include/storage/pmsignal.h
index e8ba72a253f..688b83adab1 100644
--- a/src/include/storage/pmsignal.h
+++ b/src/include/storage/pmsignal.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/storage/pmsignal.h,v 1.6 2003/11/29 22:41:13 pgsql Exp $
+ * $PostgreSQL: pgsql/src/include/storage/pmsignal.h,v 1.7 2004/05/23 03:50:45 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -24,7 +24,7 @@ typedef enum
 {
 	PMSIGNAL_DO_CHECKPOINT,		/* request to start a checkpoint */
 	PMSIGNAL_PASSWORD_CHANGE,	/* pg_pwd file has changed */
-	PMSIGNAL_WAKEN_CHILDREN,	/* send a NOTIFY signal to all backends */
+	PMSIGNAL_WAKEN_CHILDREN,	/* send a SIGUSR1 signal to all backends */
 
 	NUM_PMSIGNALS				/* Must be last value of enum! */
 } PMSignalReason;
diff --git a/src/include/storage/sinval.h b/src/include/storage/sinval.h
index 84706272dec..a1c731024cf 100644
--- a/src/include/storage/sinval.h
+++ b/src/include/storage/sinval.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/storage/sinval.h,v 1.33 2004/02/10 01:55:26 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/storage/sinval.h,v 1.34 2004/05/23 03:50:45 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -99,10 +99,19 @@ extern bool DatabaseHasActiveBackends(Oid databaseId, bool ignoreMyself);
 extern bool TransactionIdIsInProgress(TransactionId xid);
 extern TransactionId GetOldestXmin(bool allDbs);
 extern int	CountActiveBackends(void);
-
+extern int	CountEmptyBackendSlots(void);
 /* Use "struct PGPROC", not PGPROC, to avoid including proc.h here */
 extern struct PGPROC *BackendIdGetProc(BackendId procId);
 
-extern int	CountEmptyBackendSlots(void);
+/* signal handler for catchup events (SIGUSR1) */
+extern void CatchupInterruptHandler(SIGNAL_ARGS);
+
+/*
+ * enable/disable processing of catchup events directly from signal handler.
+ * The enable routine first performs processing of any catchup events that
+ * have occurred since the last disable.
+ */
+extern void EnableCatchupInterrupt(void);
+extern bool DisableCatchupInterrupt(void);
 
 #endif   /* SINVAL_H */