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Introduce latches. A latch is a boolean variable, with the capability to
wait until it is set. Latches can be used to reliably wait until a signal arrives, which is hard otherwise because signals don't interrupt select() on some platforms, and even when they do, there's race conditions. On Unix, latches use the so called self-pipe trick under the covers to implement the sleep until the latch is set, without race conditions. On Windows, Windows events are used. Use the new latch abstraction to sleep in walsender, so that as soon as a transaction finishes, walsender is woken up to immediately send the WAL to the standby. This reduces the latency between master and standby, which is good. Preliminary work by Fujii Masao. The latch implementation is by me, with helpful comments from many people.
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‎configure

Lines changed: 9 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -27773,6 +27773,13 @@ _ACEOF
2777327773
SHMEM_IMPLEMENTATION="src/backend/port/win32_shmem.c"
2777427774
fi
2777527775

27776+
# Select latch implementation type.
27777+
if test "$PORTNAME" != "win32"; then
27778+
LATCH_IMPLEMENTATION="src/backend/port/unix_latch.c"
27779+
else
27780+
LATCH_IMPLEMENTATION="src/backend/port/win32_latch.c"
27781+
fi
27782+
2777627783
# If not set in template file, set bytes to use libc memset()
2777727784
if test x"$MEMSET_LOOP_LIMIT" = x"" ; then
2777827785
MEMSET_LOOP_LIMIT=1024
@@ -29098,7 +29105,7 @@ fi
2909829105
ac_config_files="$ac_config_files GNUmakefile src/Makefile.global"
2909929106

2910029107

29101-
ac_config_links="$ac_config_links src/backend/port/dynloader.c:src/backend/port/dynloader/${template}.c src/backend/port/pg_sema.c:${SEMA_IMPLEMENTATION} src/backend/port/pg_shmem.c:${SHMEM_IMPLEMENTATION} src/include/dynloader.h:src/backend/port/dynloader/${template}.h src/include/pg_config_os.h:src/include/port/${template}.h src/Makefile.port:src/makefiles/Makefile.${template}"
29108+
ac_config_links="$ac_config_links src/backend/port/dynloader.c:src/backend/port/dynloader/${template}.c src/backend/port/pg_sema.c:${SEMA_IMPLEMENTATION} src/backend/port/pg_shmem.c:${SHMEM_IMPLEMENTATION} src/backend/port/pg_latch.c:${LATCH_IMPLEMENTATION} src/include/dynloader.h:src/backend/port/dynloader/${template}.h src/include/pg_config_os.h:src/include/port/${template}.h src/Makefile.port:src/makefiles/Makefile.${template}"
2910229109

2910329110

2910429111
if test "$PORTNAME" = "win32"; then
@@ -29722,6 +29729,7 @@ do
2972229729
"src/backend/port/dynloader.c") CONFIG_LINKS="$CONFIG_LINKS src/backend/port/dynloader.c:src/backend/port/dynloader/${template}.c" ;;
2972329730
"src/backend/port/pg_sema.c") CONFIG_LINKS="$CONFIG_LINKS src/backend/port/pg_sema.c:${SEMA_IMPLEMENTATION}" ;;
2972429731
"src/backend/port/pg_shmem.c") CONFIG_LINKS="$CONFIG_LINKS src/backend/port/pg_shmem.c:${SHMEM_IMPLEMENTATION}" ;;
29732+
"src/backend/port/pg_latch.c") CONFIG_LINKS="$CONFIG_LINKS src/backend/port/pg_latch.c:${LATCH_IMPLEMENTATION}" ;;
2972529733
"src/include/dynloader.h") CONFIG_LINKS="$CONFIG_LINKS src/include/dynloader.h:src/backend/port/dynloader/${template}.h" ;;
2972629734
"src/include/pg_config_os.h") CONFIG_LINKS="$CONFIG_LINKS src/include/pg_config_os.h:src/include/port/${template}.h" ;;
2972729735
"src/Makefile.port") CONFIG_LINKS="$CONFIG_LINKS src/Makefile.port:src/makefiles/Makefile.${template}" ;;

‎configure.in

Lines changed: 9 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,5 @@
11
dnl Process this file with autoconf to produce a configure script.
2-
dnl $PostgreSQL: pgsql/configure.in,v 1.633 2010/07/09 04:10:58 tgl Exp $
2+
dnl $PostgreSQL: pgsql/configure.in,v 1.634 2010/09/11 15:48:04 heikki Exp $
33
dnl
44
dnl Developers, please strive to achieve this order:
55
dnl
@@ -1700,6 +1700,13 @@ else
17001700
SHMEM_IMPLEMENTATION="src/backend/port/win32_shmem.c"
17011701
fi
17021702

1703+
# Select latch implementation type.
1704+
if test "$PORTNAME" != "win32"; then
1705+
LATCH_IMPLEMENTATION="src/backend/port/unix_latch.c"
1706+
else
1707+
LATCH_IMPLEMENTATION="src/backend/port/win32_latch.c"
1708+
fi
1709+
17031710
# If not set in template file, set bytes to use libc memset()
17041711
if test x"$MEMSET_LOOP_LIMIT" = x"" ; then
17051712
MEMSET_LOOP_LIMIT=1024
@@ -1841,6 +1848,7 @@ AC_CONFIG_LINKS([
18411848
src/backend/port/dynloader.c:src/backend/port/dynloader/${template}.c
18421849
src/backend/port/pg_sema.c:${SEMA_IMPLEMENTATION}
18431850
src/backend/port/pg_shmem.c:${SHMEM_IMPLEMENTATION}
1851+
src/backend/port/pg_latch.c:${LATCH_IMPLEMENTATION}
18441852
src/include/dynloader.h:src/backend/port/dynloader/${template}.h
18451853
src/include/pg_config_os.h:src/include/port/${template}.h
18461854
src/Makefile.port:src/makefiles/Makefile.${template}

‎src/backend/access/transam/twophase.c

Lines changed: 23 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
* Portions Copyright (c) 1994, Regents of the University of California
88
*
99
* IDENTIFICATION
10-
* $PostgreSQL: pgsql/src/backend/access/transam/twophase.c,v 1.63 2010/08/13 20:10:50 rhaas Exp $
10+
* $PostgreSQL: pgsql/src/backend/access/transam/twophase.c,v 1.64 2010/09/11 15:48:04 heikki Exp $
1111
*
1212
* NOTES
1313
* Each global transaction is associated with a global transaction
@@ -55,6 +55,7 @@
5555
#include "miscadmin.h"
5656
#include "pg_trace.h"
5757
#include "pgstat.h"
58+
#include "replication/walsender.h"
5859
#include "storage/fd.h"
5960
#include "storage/procarray.h"
6061
#include "storage/sinvaladt.h"
@@ -1025,6 +1026,13 @@ EndPrepare(GlobalTransaction gxact)
10251026

10261027
/* If we crash now, we have prepared: WAL replay will fix things */
10271028

1029+
/*
1030+
* Wake up all walsenders to send WAL up to the PREPARE record
1031+
* immediately if replication is enabled
1032+
*/
1033+
if (max_wal_senders > 0)
1034+
WalSndWakeup();
1035+
10281036
/* write correct CRC and close file */
10291037
if ((write(fd, &statefile_crc, sizeof(pg_crc32))) != sizeof(pg_crc32))
10301038
{
@@ -2005,6 +2013,13 @@ RecordTransactionCommitPrepared(TransactionId xid,
20052013
/* Flush XLOG to disk */
20062014
XLogFlush(recptr);
20072015

2016+
/*
2017+
* Wake up all walsenders to send WAL up to the COMMIT PREPARED record
2018+
* immediately if replication is enabled
2019+
*/
2020+
if (max_wal_senders > 0)
2021+
WalSndWakeup();
2022+
20082023
/* Mark the transaction committed in pg_clog */
20092024
TransactionIdCommitTree(xid, nchildren, children);
20102025

@@ -2077,6 +2092,13 @@ RecordTransactionAbortPrepared(TransactionId xid,
20772092
/* Always flush, since we're about to remove the 2PC state file */
20782093
XLogFlush(recptr);
20792094

2095+
/*
2096+
* Wake up all walsenders to send WAL up to the ABORT PREPARED record
2097+
* immediately if replication is enabled
2098+
*/
2099+
if (max_wal_senders > 0)
2100+
WalSndWakeup();
2101+
20802102
/*
20812103
* Mark the transaction aborted in clog. This is not absolutely necessary
20822104
* but we may as well do it while we are here.

‎src/backend/access/transam/xact.c

Lines changed: 9 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -10,7 +10,7 @@
1010
*
1111
*
1212
* IDENTIFICATION
13-
* $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.298 2010/08/13 20:10:50 rhaas Exp $
13+
* $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.299 2010/09/11 15:48:04 heikki Exp $
1414
*
1515
*-------------------------------------------------------------------------
1616
*/
@@ -36,6 +36,7 @@
3636
#include "libpq/be-fsstubs.h"
3737
#include "miscadmin.h"
3838
#include "pgstat.h"
39+
#include "replication/walsender.h"
3940
#include "storage/bufmgr.h"
4041
#include "storage/fd.h"
4142
#include "storage/lmgr.h"
@@ -1067,6 +1068,13 @@ RecordTransactionCommit(void)
10671068

10681069
XLogFlush(XactLastRecEnd);
10691070

1071+
/*
1072+
* Wake up all walsenders to send WAL up to the COMMIT record
1073+
* immediately if replication is enabled
1074+
*/
1075+
if (max_wal_senders > 0)
1076+
WalSndWakeup();
1077+
10701078
/*
10711079
* Now we may update the CLOG, if we wrote a COMMIT record above
10721080
*/

‎src/backend/port/Makefile

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -13,15 +13,15 @@
1313
# be converted to Method 2.
1414
#
1515
# IDENTIFICATION
16-
# $PostgreSQL: pgsql/src/backend/port/Makefile,v 1.28 2010/07/05 18:54:37 tgl Exp $
16+
# $PostgreSQL: pgsql/src/backend/port/Makefile,v 1.29 2010/09/11 15:48:04 heikki Exp $
1717
#
1818
#-------------------------------------------------------------------------
1919

2020
subdir = src/backend/port
2121
top_builddir = ../../..
2222
include $(top_builddir)/src/Makefile.global
2323

24-
OBJS = dynloader.o pg_sema.o pg_shmem.o $(TAS)
24+
OBJS = dynloader.o pg_sema.o pg_shmem.o pg_latch.o $(TAS)
2525

2626
ifeq ($(PORTNAME), darwin)
2727
SUBDIRS += darwin

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