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.

4 files changed, 14 insertions, 7 deletions

diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index f0d8666091d..2d5dd7b2b5c 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -15,7 +15,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/nodes/copyfuncs.c,v 1.303 2005/04/25 01:30:13 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/nodes/copyfuncs.c,v 1.304 2005/04/28 21:47:12 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1605,6 +1605,7 @@ _copyQuery(Query *from)
 	COPY_NODE_FIELD(rtable);
 	COPY_NODE_FIELD(jointree);
 	COPY_NODE_FIELD(rowMarks);
+	COPY_SCALAR_FIELD(forUpdate);
 	COPY_NODE_FIELD(targetList);
 	COPY_NODE_FIELD(groupClause);
 	COPY_NODE_FIELD(havingQual);
@@ -1685,7 +1686,8 @@ _copySelectStmt(SelectStmt *from)
 	COPY_NODE_FIELD(sortClause);
 	COPY_NODE_FIELD(limitOffset);
 	COPY_NODE_FIELD(limitCount);
-	COPY_NODE_FIELD(forUpdate);
+	COPY_NODE_FIELD(lockedRels);
+	COPY_SCALAR_FIELD(forUpdate);
 	COPY_SCALAR_FIELD(op);
 	COPY_SCALAR_FIELD(all);
 	COPY_NODE_FIELD(larg);
diff --git a/src/backend/nodes/equalfuncs.c b/src/backend/nodes/equalfuncs.c
index fb599097005..a9570201be2 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -18,7 +18,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/nodes/equalfuncs.c,v 1.240 2005/04/07 01:51:38 neilc Exp $
+ *	  $PostgreSQL: pgsql/src/backend/nodes/equalfuncs.c,v 1.241 2005/04/28 21:47:12 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -642,6 +642,7 @@ _equalQuery(Query *a, Query *b)
 	COMPARE_NODE_FIELD(rtable);
 	COMPARE_NODE_FIELD(jointree);
 	COMPARE_NODE_FIELD(rowMarks);
+	COMPARE_SCALAR_FIELD(forUpdate);
 	COMPARE_NODE_FIELD(targetList);
 	COMPARE_NODE_FIELD(groupClause);
 	COMPARE_NODE_FIELD(havingQual);
@@ -706,7 +707,8 @@ _equalSelectStmt(SelectStmt *a, SelectStmt *b)
 	COMPARE_NODE_FIELD(sortClause);
 	COMPARE_NODE_FIELD(limitOffset);
 	COMPARE_NODE_FIELD(limitCount);
-	COMPARE_NODE_FIELD(forUpdate);
+	COMPARE_NODE_FIELD(lockedRels);
+	COMPARE_SCALAR_FIELD(forUpdate);
 	COMPARE_SCALAR_FIELD(op);
 	COMPARE_SCALAR_FIELD(all);
 	COMPARE_NODE_FIELD(larg);
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index 484551a8503..2dc676b8d43 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/nodes/outfuncs.c,v 1.250 2005/04/25 01:30:13 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/nodes/outfuncs.c,v 1.251 2005/04/28 21:47:13 tgl Exp $
  *
  * NOTES
  *	  Every node type that can appear in stored rules' parsetrees *must*
@@ -1268,7 +1268,8 @@ _outSelectStmt(StringInfo str, SelectStmt *node)
 	WRITE_NODE_FIELD(sortClause);
 	WRITE_NODE_FIELD(limitOffset);
 	WRITE_NODE_FIELD(limitCount);
-	WRITE_NODE_FIELD(forUpdate);
+	WRITE_NODE_FIELD(lockedRels);
+	WRITE_BOOL_FIELD(forUpdate);
 	WRITE_ENUM_FIELD(op, SetOperation);
 	WRITE_BOOL_FIELD(all);
 	WRITE_NODE_FIELD(larg);
@@ -1385,6 +1386,7 @@ _outQuery(StringInfo str, Query *node)
 	WRITE_NODE_FIELD(rtable);
 	WRITE_NODE_FIELD(jointree);
 	WRITE_NODE_FIELD(rowMarks);
+	WRITE_BOOL_FIELD(forUpdate);
 	WRITE_NODE_FIELD(targetList);
 	WRITE_NODE_FIELD(groupClause);
 	WRITE_NODE_FIELD(havingQual);
diff --git a/src/backend/nodes/readfuncs.c b/src/backend/nodes/readfuncs.c
index f457d063315..ef405f7a022 100644
--- a/src/backend/nodes/readfuncs.c
+++ b/src/backend/nodes/readfuncs.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/nodes/readfuncs.c,v 1.176 2005/04/06 16:34:05 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/nodes/readfuncs.c,v 1.177 2005/04/28 21:47:13 tgl Exp $
  *
  * NOTES
  *	  Path and Plan nodes do not have any readfuncs support, because we
@@ -145,6 +145,7 @@ _readQuery(void)
 	READ_NODE_FIELD(rtable);
 	READ_NODE_FIELD(jointree);
 	READ_NODE_FIELD(rowMarks);
+	READ_BOOL_FIELD(forUpdate);
 	READ_NODE_FIELD(targetList);
 	READ_NODE_FIELD(groupClause);
 	READ_NODE_FIELD(havingQual);