Improve concurrency of foreign key locking

This patch introduces two additional lock modes for tuples: "SELECT FOR
KEY SHARE" and "SELECT FOR NO KEY UPDATE".  These don't block each
other, in contrast with already existing "SELECT FOR SHARE" and "SELECT
FOR UPDATE".  UPDATE commands that do not modify the values stored in
the columns that are part of the key of the tuple now grab a SELECT FOR
NO KEY UPDATE lock on the tuple, allowing them to proceed concurrently
with tuple locks of the FOR KEY SHARE variety.

Foreign key triggers now use FOR KEY SHARE instead of FOR SHARE; this
means the concurrency improvement applies to them, which is the whole
point of this patch.

The added tuple lock semantics require some rejiggering of the multixact
module, so that the locking level that each transaction is holding can
be stored alongside its Xid.  Also, multixacts now need to persist
across server restarts and crashes, because they can now represent not
only tuple locks, but also tuple updates.  This means we need more
careful tracking of lifetime of pg_multixact SLRU files; since they now
persist longer, we require more infrastructure to figure out when they
can be removed.  pg_upgrade also needs to be careful to copy
pg_multixact files over from the old server to the new, or at least part
of multixact.c state, depending on the versions of the old and new
servers.

Tuple time qualification rules (HeapTupleSatisfies routines) need to be
careful not to consider tuples with the "is multi" infomask bit set as
being only locked; they might need to look up MultiXact values (i.e.
possibly do pg_multixact I/O) to find out the Xid that updated a tuple,
whereas they previously were assured to only use information readily
available from the tuple header.  This is considered acceptable, because
the extra I/O would involve cases that would previously cause some
commands to block waiting for concurrent transactions to finish.

Another important change is the fact that locking tuples that have
previously been updated causes the future versions to be marked as
locked, too; this is essential for correctness of foreign key checks.
This causes additional WAL-logging, also (there was previously a single
WAL record for a locked tuple; now there are as many as updated copies
of the tuple there exist.)

With all this in place, contention related to tuples being checked by
foreign key rules should be much reduced.

As a bonus, the old behavior that a subtransaction grabbing a stronger
tuple lock than the parent (sub)transaction held on a given tuple and
later aborting caused the weaker lock to be lost, has been fixed.

Many new spec files were added for isolation tester framework, to ensure
overall behavior is sane.  There's probably room for several more tests.

There were several reviewers of this patch; in particular, Noah Misch
and Andres Freund spent considerable time in it.  Original idea for the
patch came from Simon Riggs, after a problem report by Joel Jacobson.
Most code is from me, with contributions from Marti Raudsepp, Alexander
Shulgin, Noah Misch and Andres Freund.

This patch was discussed in several pgsql-hackers threads; the most
important start at the following message-ids:
	AANLkTimo9XVcEzfiBR-ut3KVNDkjm2Vxh+t8kAmWjPuv@mail.gmail.com
	1290721684-sup-3951@alvh.no-ip.org
	1294953201-sup-2099@alvh.no-ip.org
	1320343602-sup-2290@alvh.no-ip.org
	1339690386-sup-8927@alvh.no-ip.org
	4FE5FF020200002500048A3D@gw.wicourts.gov
	4FEAB90A0200002500048B7D@gw.wicourts.gov

1 files changed, 29 insertions, 29 deletions

diff --git a/src/backend/parser/analyze.c b/src/backend/parser/analyze.c
index 5aa6ecce7b3..ede41af6dbc 100644
--- a/src/backend/parser/analyze.c
+++ b/src/backend/parser/analyze.c
@@ -2139,7 +2139,7 @@ transformCreateTableAsStmt(ParseState *pstate, CreateTableAsStmt *stmt)
 
 
 /*
- * Check for features that are not supported together with FOR UPDATE/SHARE.
+ * Check for features that are not supported together with FOR [KEY] UPDATE/SHARE.
  *
  * exported so planner can check again after rewriting, query pullup, etc
  */
@@ -2149,35 +2149,35 @@ CheckSelectLocking(Query *qry)
 	if (qry->setOperations)
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-				 errmsg("SELECT FOR UPDATE/SHARE is not allowed with UNION/INTERSECT/EXCEPT")));
+				 errmsg("SELECT FOR UPDATE/SHARE/FOR KEY UPDATE/FOR KEY SHARE is not allowed with UNION/INTERSECT/EXCEPT")));
 	if (qry->distinctClause != NIL)
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-				 errmsg("SELECT FOR UPDATE/SHARE is not allowed with DISTINCT clause")));
+				 errmsg("SELECT FOR UPDATE/SHARE/FOR KEY UPDATE/FOR KEY SHARE is not allowed with DISTINCT clause")));
 	if (qry->groupClause != NIL)
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-				 errmsg("SELECT FOR UPDATE/SHARE is not allowed with GROUP BY clause")));
+				 errmsg("SELECT FOR UPDATE/SHARE/FOR KEY UPDATE/FOR KEY SHARE is not allowed with GROUP BY clause")));
 	if (qry->havingQual != NULL)
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-		errmsg("SELECT FOR UPDATE/SHARE is not allowed with HAVING clause")));
+		errmsg("SELECT FOR UPDATE/SHARE/FOR KEY UPDATE/FOR KEY SHARE is not allowed with HAVING clause")));
 	if (qry->hasAggs)
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-				 errmsg("SELECT FOR UPDATE/SHARE is not allowed with aggregate functions")));
+				 errmsg("SELECT FOR UPDATE/SHARE/FOR KEY UPDATE/FOR KEY SHARE is not allowed with aggregate functions")));
 	if (qry->hasWindowFuncs)
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-				 errmsg("SELECT FOR UPDATE/SHARE is not allowed with window functions")));
+				 errmsg("SELECT FOR UPDATE/SHARE/FOR KEY UPDATE/FOR KEY SHARE is not allowed with window functions")));
 	if (expression_returns_set((Node *) qry->targetList))
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-				 errmsg("SELECT FOR UPDATE/SHARE is not allowed with set-returning functions in the target list")));
+				 errmsg("SELECT FOR UPDATE/SHARE/FOR KEY UPDATE/FOR KEY SHARE is not allowed with set-returning functions in the target list")));
 }
 
 /*
- * Transform a FOR UPDATE/SHARE clause
+ * Transform a FOR [KEY] UPDATE/SHARE clause
  *
  * This basically involves replacing names by integer relids.
  *
@@ -2199,7 +2199,7 @@ transformLockingClause(ParseState *pstate, Query *qry, LockingClause *lc,
 	/* make a clause we can pass down to subqueries to select all rels */
 	allrels = makeNode(LockingClause);
 	allrels->lockedRels = NIL;	/* indicates all rels */
-	allrels->forUpdate = lc->forUpdate;
+	allrels->strength = lc->strength;
 	allrels->noWait = lc->noWait;
 
 	if (lockedRels == NIL)
@@ -2218,15 +2218,15 @@ transformLockingClause(ParseState *pstate, Query *qry, LockingClause *lc,
 					if (rte->relkind == RELKIND_FOREIGN_TABLE)
 						break;
 					applyLockingClause(qry, i,
-									   lc->forUpdate, lc->noWait, pushedDown);
+									   lc->strength, lc->noWait, pushedDown);
 					rte->requiredPerms |= ACL_SELECT_FOR_UPDATE;
 					break;
 				case RTE_SUBQUERY:
 					applyLockingClause(qry, i,
-									   lc->forUpdate, lc->noWait, pushedDown);
+									   lc->strength, lc->noWait, pushedDown);
 
 					/*
-					 * FOR UPDATE/SHARE of subquery is propagated to all of
+					 * FOR [KEY] UPDATE/SHARE of subquery is propagated to all of
 					 * subquery's rels, too.  We could do this later (based on
 					 * the marking of the subquery RTE) but it is convenient
 					 * to have local knowledge in each query level about which
@@ -2252,7 +2252,7 @@ transformLockingClause(ParseState *pstate, Query *qry, LockingClause *lc,
 			if (thisrel->catalogname || thisrel->schemaname)
 				ereport(ERROR,
 						(errcode(ERRCODE_SYNTAX_ERROR),
-						 errmsg("SELECT FOR UPDATE/SHARE must specify unqualified relation names"),
+						 errmsg("SELECT FOR UPDATE/SHARE/KEY UPDATE/KEY SHARE must specify unqualified relation names"),
 						 parser_errposition(pstate, thisrel->location)));
 
 			i = 0;
@@ -2269,17 +2269,17 @@ transformLockingClause(ParseState *pstate, Query *qry, LockingClause *lc,
 							if (rte->relkind == RELKIND_FOREIGN_TABLE)
 								ereport(ERROR,
 									 (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-									  errmsg("SELECT FOR UPDATE/SHARE cannot be used with foreign table \"%s\"",
+									  errmsg("SELECT FOR UPDATE/SHARE/KEY UPDATE/KEY SHARE cannot be used with foreign table \"%s\"",
 											 rte->eref->aliasname),
 									  parser_errposition(pstate, thisrel->location)));
 							applyLockingClause(qry, i,
-											   lc->forUpdate, lc->noWait,
+											   lc->strength, lc->noWait,
 											   pushedDown);
 							rte->requiredPerms |= ACL_SELECT_FOR_UPDATE;
 							break;
 						case RTE_SUBQUERY:
 							applyLockingClause(qry, i,
-											   lc->forUpdate, lc->noWait,
+											   lc->strength, lc->noWait,
 											   pushedDown);
 							/* see comment above */
 							transformLockingClause(pstate, rte->subquery,
@@ -2288,25 +2288,25 @@ transformLockingClause(ParseState *pstate, Query *qry, LockingClause *lc,
 						case RTE_JOIN:
 							ereport(ERROR,
 									(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-									 errmsg("SELECT FOR UPDATE/SHARE cannot be applied to a join"),
+									 errmsg("SELECT FOR UPDATE/SHARE/KEY UPDATE/KEY SHARE cannot be applied to a join"),
 							 parser_errposition(pstate, thisrel->location)));
 							break;
 						case RTE_FUNCTION:
 							ereport(ERROR,
 									(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-									 errmsg("SELECT FOR UPDATE/SHARE cannot be applied to a function"),
+									 errmsg("SELECT FOR UPDATE/SHARE/KEY UPDATE/KEY SHARE cannot be applied to a function"),
 							 parser_errposition(pstate, thisrel->location)));
 							break;
 						case RTE_VALUES:
 							ereport(ERROR,
 									(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-									 errmsg("SELECT FOR UPDATE/SHARE cannot be applied to VALUES"),
+									 errmsg("SELECT FOR UPDATE/SHARE/KEY UPDATE/KEY SHARE cannot be applied to VALUES"),
 							 parser_errposition(pstate, thisrel->location)));
 							break;
 						case RTE_CTE:
 							ereport(ERROR,
 									(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-									 errmsg("SELECT FOR UPDATE/SHARE cannot be applied to a WITH query"),
+									 errmsg("SELECT FOR UPDATE/SHARE/KEY UPDATE/KEY SHARE cannot be applied to a WITH query"),
 							 parser_errposition(pstate, thisrel->location)));
 							break;
 						default:
@@ -2320,7 +2320,7 @@ transformLockingClause(ParseState *pstate, Query *qry, LockingClause *lc,
 			if (rt == NULL)
 				ereport(ERROR,
 						(errcode(ERRCODE_UNDEFINED_TABLE),
-						 errmsg("relation \"%s\" in FOR UPDATE/SHARE clause not found in FROM clause",
+						 errmsg("relation \"%s\" in FOR UPDATE/SHARE/KEY UPDATE/KEY SHARE clause not found in FROM clause",
 								thisrel->relname),
 						 parser_errposition(pstate, thisrel->location)));
 		}
@@ -2332,7 +2332,7 @@ transformLockingClause(ParseState *pstate, Query *qry, LockingClause *lc,
  */
 void
 applyLockingClause(Query *qry, Index rtindex,
-				   bool forUpdate, bool noWait, bool pushedDown)
+				   LockClauseStrength strength, bool noWait, bool pushedDown)
 {
 	RowMarkClause *rc;
 
@@ -2344,10 +2344,10 @@ applyLockingClause(Query *qry, Index rtindex,
 	if ((rc = get_parse_rowmark(qry, rtindex)) != NULL)
 	{
 		/*
-		 * If the same RTE is specified both FOR UPDATE and FOR SHARE, treat
-		 * it as FOR UPDATE.  (Reasonable, since you can't take both a shared
-		 * and exclusive lock at the same time; it'll end up being exclusive
-		 * anyway.)
+		 * If the same RTE is specified for more than one locking strength,
+		 * treat is as the strongest.  (Reasonable, since you can't take both a
+		 * shared and exclusive lock at the same time; it'll end up being
+		 * exclusive anyway.)
 		 *
 		 * We also consider that NOWAIT wins if it's specified both ways. This
 		 * is a bit more debatable but raising an error doesn't seem helpful.
@@ -2356,7 +2356,7 @@ applyLockingClause(Query *qry, Index rtindex,
 		 *
 		 * And of course pushedDown becomes false if any clause is explicit.
 		 */
-		rc->forUpdate |= forUpdate;
+		rc->strength = Max(rc->strength, strength);
 		rc->noWait |= noWait;
 		rc->pushedDown &= pushedDown;
 		return;
@@ -2365,7 +2365,7 @@ applyLockingClause(Query *qry, Index rtindex,
 	/* Make a new RowMarkClause */
 	rc = makeNode(RowMarkClause);
 	rc->rti = rtindex;
-	rc->forUpdate = forUpdate;
+	rc->strength = strength;
 	rc->noWait = noWait;
 	rc->pushedDown = pushedDown;
 	qry->rowMarks = lappend(qry->rowMarks, rc);