Implement sharable row-level locks, and use them for foreign key references

to eliminate unnecessary deadlocks.  This commit adds SELECT ... FOR SHARE
paralleling SELECT ... FOR UPDATE.  The implementation uses a new SLRU
data structure (managed much like pg_subtrans) to represent multiple-
transaction-ID sets.  When more than one transaction is holding a shared
lock on a particular row, we create a MultiXactId representing that set
of transactions and store its ID in the row's XMAX.  This scheme allows
an effectively unlimited number of row locks, just as we did before,
while not costing any extra overhead except when a shared lock actually
has to be shared.   Still TODO: use the regular lock manager to control
the grant order when multiple backends are waiting for a row lock.

Alvaro Herrera and Tom Lane.

1 files changed, 25 insertions, 2 deletions

diff --git a/src/bin/pg_resetxlog/pg_resetxlog.c b/src/bin/pg_resetxlog/pg_resetxlog.c
index c47a35340d..cabc5c0012 100644
--- a/src/bin/pg_resetxlog/pg_resetxlog.c
+++ b/src/bin/pg_resetxlog/pg_resetxlog.c
@@ -23,7 +23,7 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/bin/pg_resetxlog/pg_resetxlog.c,v 1.31 2005/04/13 18:54:56 tgl Exp $
+ * $PostgreSQL: pgsql/src/bin/pg_resetxlog/pg_resetxlog.c,v 1.32 2005/04/28 21:47:16 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -40,6 +40,7 @@
 #include <getopt.h>
 #endif
 
+#include "access/multixact.h"
 #include "access/xlog.h"
 #include "access/xlog_internal.h"
 #include "catalog/catversion.h"
@@ -75,6 +76,7 @@ main(int argc, char *argv[])
 	bool		noupdate = false;
 	TransactionId set_xid = 0;
 	Oid			set_oid = 0;
+	MultiXactId	set_mxid = 0;
 	uint32		minXlogTli = 0,
 				minXlogId = 0,
 				minXlogSeg = 0;
@@ -104,7 +106,7 @@ main(int argc, char *argv[])
 	}
 
 
-	while ((c = getopt(argc, argv, "fl:no:x:")) != -1)
+	while ((c = getopt(argc, argv, "fl:m:no:x:")) != -1)
 	{
 		switch (c)
 		{
@@ -146,6 +148,21 @@ main(int argc, char *argv[])
 				}
 				break;
 
+			case 'm':
+				set_mxid = strtoul(optarg, &endptr, 0);
+				if (endptr == optarg || *endptr != '\0')
+				{
+					fprintf(stderr, _("%s: invalid argument for option -m\n"), progname);
+					fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
+					exit(1);
+				}
+				if (set_mxid == 0)
+				{
+					fprintf(stderr, _("%s: multi transaction ID (-m) must not be 0\n"), progname);
+					exit(1);
+				}
+				break;
+
 			case 'l':
 				minXlogTli = strtoul(optarg, &endptr, 0);
 				if (endptr == optarg || *endptr != ',')
@@ -245,6 +262,9 @@ main(int argc, char *argv[])
 	if (set_oid != 0)
 		ControlFile.checkPointCopy.nextOid = set_oid;
 
+	if (set_mxid != 0)
+		ControlFile.checkPointCopy.nextMulti = set_mxid;
+
 	if (minXlogTli > ControlFile.checkPointCopy.ThisTimeLineID)
 		ControlFile.checkPointCopy.ThisTimeLineID = minXlogTli;
 
@@ -405,6 +425,7 @@ GuessControlValues(void)
 	ControlFile.checkPointCopy.ThisTimeLineID = 1;
 	ControlFile.checkPointCopy.nextXid = (TransactionId) 514;	/* XXX */
 	ControlFile.checkPointCopy.nextOid = FirstBootstrapObjectId;
+	ControlFile.checkPointCopy.nextMulti = FirstMultiXactId;
 	ControlFile.checkPointCopy.time = time(NULL);
 
 	ControlFile.state = DB_SHUTDOWNED;
@@ -478,6 +499,7 @@ PrintControlValues(bool guessed)
 	printf(_("Latest checkpoint's TimeLineID:       %u\n"), ControlFile.checkPointCopy.ThisTimeLineID);
 	printf(_("Latest checkpoint's NextXID:          %u\n"), ControlFile.checkPointCopy.nextXid);
 	printf(_("Latest checkpoint's NextOID:          %u\n"), ControlFile.checkPointCopy.nextOid);
+	printf(_("Latest checkpoint's NextMultiXactId:  %u\n"), ControlFile.checkPointCopy.nextMulti);
 	printf(_("Database block size:                  %u\n"), ControlFile.blcksz);
 	printf(_("Blocks per segment of large relation: %u\n"), ControlFile.relseg_size);
 	printf(_("Maximum length of identifiers:        %u\n"), ControlFile.nameDataLen);
@@ -753,6 +775,7 @@ usage(void)
 	printf(_("  -n              no update, just show extracted control values (for testing)\n"));
 	printf(_("  -o OID          set next OID\n"));
 	printf(_("  -x XID          set next transaction ID\n"));
+	printf(_("  -m multiXID     set next multi transaction ID\n"));
 	printf(_("  --help          show this help, then exit\n"));
 	printf(_("  --version       output version information, then exit\n"));
 	printf(_("\nReport bugs to <pgsql-bugs@postgresql.org>.\n"));