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, 23 insertions, 13 deletions

diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index 56cf592e0ce..d8678e5b3fd 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -74,7 +74,7 @@ typedef uint32 AclMode;			/* a bitmask of privilege bits */
 #define ACL_CONNECT		(1<<11) /* for databases */
 #define N_ACL_RIGHTS	12		/* 1 plus the last 1<<x */
 #define ACL_NO_RIGHTS	0
-/* Currently, SELECT ... FOR UPDATE/FOR SHARE requires UPDATE privileges */
+/* Currently, SELECT ... FOR [KEY] UPDATE/SHARE requires UPDATE privileges */
 #define ACL_SELECT_FOR_UPDATE	ACL_UPDATE
 
 
@@ -119,7 +119,7 @@ typedef struct Query
 	bool		hasDistinctOn;	/* distinctClause is from DISTINCT ON */
 	bool		hasRecursive;	/* WITH RECURSIVE was specified */
 	bool		hasModifyingCTE;	/* has INSERT/UPDATE/DELETE in WITH */
-	bool		hasForUpdate;	/* FOR UPDATE or FOR SHARE was specified */
+	bool		hasForUpdate;	/* FOR [KEY] UPDATE/SHARE was specified */
 
 	List	   *cteList;		/* WITH list (of CommonTableExpr's) */
 
@@ -572,18 +572,28 @@ typedef struct DefElem
 } DefElem;
 
 /*
- * LockingClause - raw representation of FOR UPDATE/SHARE options
+ * LockingClause - raw representation of FOR [NO KEY] UPDATE/[KEY] SHARE
+ * 		options
  *
  * Note: lockedRels == NIL means "all relations in query".	Otherwise it
  * is a list of RangeVar nodes.  (We use RangeVar mainly because it carries
  * a location field --- currently, parse analysis insists on unqualified
  * names in LockingClause.)
  */
+typedef enum LockClauseStrength
+{
+	/* order is important -- see applyLockingClause */
+	LCS_FORKEYSHARE,
+	LCS_FORSHARE,
+	LCS_FORNOKEYUPDATE,
+	LCS_FORUPDATE
+} LockClauseStrength;
+
 typedef struct LockingClause
 {
 	NodeTag		type;
-	List	   *lockedRels;		/* FOR UPDATE or FOR SHARE relations */
-	bool		forUpdate;		/* true = FOR UPDATE, false = FOR SHARE */
+	List	   *lockedRels;		/* FOR [KEY] UPDATE/SHARE relations */
+	LockClauseStrength strength;
 	bool		noWait;			/* NOWAIT option */
 } LockingClause;
 
@@ -865,21 +875,21 @@ typedef struct WindowClause
 
 /*
  * RowMarkClause -
- *	   parser output representation of FOR UPDATE/SHARE clauses
+ *	   parser output representation of FOR [KEY] UPDATE/SHARE clauses
  *
  * Query.rowMarks contains a separate RowMarkClause node for each relation
- * identified as a FOR UPDATE/SHARE target.  If FOR UPDATE/SHARE is applied
- * to a subquery, we generate RowMarkClauses for all normal and subquery rels
- * in the subquery, but they are marked pushedDown = true to distinguish them
- * from clauses that were explicitly written at this query level.  Also,
- * Query.hasForUpdate tells whether there were explicit FOR UPDATE/SHARE
- * clauses in the current query level.
+ * identified as a FOR [KEY] UPDATE/SHARE target.  If one of these clauses
+ * is applied to a subquery, we generate RowMarkClauses for all normal and
+ * subquery rels in the subquery, but they are marked pushedDown = true to
+ * distinguish them from clauses that were explicitly written at this query
+ * level.  Also, Query.hasForUpdate tells whether there were explicit FOR
+ * UPDATE/SHARE/KEY SHARE clauses in the current query level.
  */
 typedef struct RowMarkClause
 {
 	NodeTag		type;
 	Index		rti;			/* range table index of target relation */
-	bool		forUpdate;		/* true = FOR UPDATE, false = FOR SHARE */
+	LockClauseStrength strength;
 	bool		noWait;			/* NOWAIT option */
 	bool		pushedDown;		/* pushed down from higher query level? */
 } RowMarkClause;