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, 2 insertions, 2 deletions

diff --git a/src/include/parser/parse_node.h b/src/include/parser/parse_node.h
index 3999918f248..bfcf00fd47d 100644
--- a/src/include/parser/parse_node.h
+++ b/src/include/parser/parse_node.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/parser/parse_node.h,v 1.42 2004/12/31 22:03:38 pgsql Exp $
+ * $PostgreSQL: pgsql/src/include/parser/parse_node.h,v 1.43 2005/04/28 21:47:18 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -53,7 +53,7 @@ typedef struct ParseState
 	Oid		   *p_paramtypes;	/* OIDs of types for $n parameter symbols */
 	int			p_numparams;	/* allocated size of p_paramtypes[] */
 	int			p_next_resno;	/* next targetlist resno to assign */
-	List	   *p_forUpdate;	/* FOR UPDATE clause, if any (see gram.y) */
+	List	   *p_lockedRels;	/* FOR UPDATE/SHARE, if any (see gram.y) */
 	Node	   *p_value_substitute;		/* what to replace VALUE with, if
 										 * any */
 	bool		p_variableparams;