Add support for INSERT ... ON CONFLICT DO NOTHING/UPDATE.

The newly added ON CONFLICT clause allows to specify an alternative to
raising a unique or exclusion constraint violation error when inserting.
ON CONFLICT refers to constraints that can either be specified using a
inference clause (by specifying the columns of a unique constraint) or
by naming a unique or exclusion constraint.  DO NOTHING avoids the
constraint violation, without touching the pre-existing row.  DO UPDATE
SET ... [WHERE ...] updates the pre-existing tuple, and has access to
both the tuple proposed for insertion and the existing tuple; the
optional WHERE clause can be used to prevent an update from being
executed.  The UPDATE SET and WHERE clauses have access to the tuple
proposed for insertion using the "magic" EXCLUDED alias, and to the
pre-existing tuple using the table name or its alias.

This feature is often referred to as upsert.

This is implemented using a new infrastructure called "speculative
insertion". It is an optimistic variant of regular insertion that first
does a pre-check for existing tuples and then attempts an insert.  If a
violating tuple was inserted concurrently, the speculatively inserted
tuple is deleted and a new attempt is made.  If the pre-check finds a
matching tuple the alternative DO NOTHING or DO UPDATE action is taken.
If the insertion succeeds without detecting a conflict, the tuple is
deemed inserted.

To handle the possible ambiguity between the excluded alias and a table
named excluded, and for convenience with long relation names, INSERT
INTO now can alias its target table.

Bumps catversion as stored rules change.

Author: Peter Geoghegan, with significant contributions from Heikki
    Linnakangas and Andres Freund. Testing infrastructure by Jeff Janes.
Reviewed-By: Heikki Linnakangas, Andres Freund, Robert Haas, Simon Riggs,
    Dean Rasheed, Stephen Frost and many others.

1 files changed, 27 insertions, 2 deletions

diff --git a/src/backend/utils/time/tqual.c b/src/backend/utils/time/tqual.c
index a4a478d114..b4284d6d94 100644
--- a/src/backend/utils/time/tqual.c
+++ b/src/backend/utils/time/tqual.c
@@ -405,6 +405,13 @@ HeapTupleSatisfiesToast(HeapTuple htup, Snapshot snapshot,
 				}
 			}
 		}
+		/*
+		 * An invalid Xmin can be left behind by a speculative insertion that
+		 * is cancelled by super-deleting the tuple.  We shouldn't see any of
+		 * those in TOAST tables, but better safe than sorry.
+		 */
+		else if (!TransactionIdIsValid(HeapTupleHeaderGetXmin(tuple)))
+			return false;
 	}
 
 	/* otherwise assume the tuple is valid for TOAST. */
@@ -714,8 +721,11 @@ HeapTupleSatisfiesUpdate(HeapTuple htup, CommandId curcid,
  * output argument to return the xids of concurrent xacts that affected the
  * tuple.  snapshot->xmin is set to the tuple's xmin if that is another
  * transaction that's still in progress; or to InvalidTransactionId if the
- * tuple's xmin is committed good, committed dead, or my own xact.  Similarly
- * for snapshot->xmax and the tuple's xmax.
+ * tuple's xmin is committed good, committed dead, or my own xact.
+ * Similarly for snapshot->xmax and the tuple's xmax.  If the tuple was
+ * inserted speculatively, meaning that the inserter might still back down
+ * on the insertion without aborting the whole transaction, the associated
+ * token is also returned in snapshot->speculativeToken.
  */
 bool
 HeapTupleSatisfiesDirty(HeapTuple htup, Snapshot snapshot,
@@ -727,6 +737,7 @@ HeapTupleSatisfiesDirty(HeapTuple htup, Snapshot snapshot,
 	Assert(htup->t_tableOid != InvalidOid);
 
 	snapshot->xmin = snapshot->xmax = InvalidTransactionId;
+	snapshot->speculativeToken = 0;
 
 	if (!HeapTupleHeaderXminCommitted(tuple))
 	{
@@ -808,6 +819,20 @@ HeapTupleSatisfiesDirty(HeapTuple htup, Snapshot snapshot,
 		}
 		else if (TransactionIdIsInProgress(HeapTupleHeaderGetRawXmin(tuple)))
 		{
+			/*
+			 * Return the speculative token to caller.  Caller can worry
+			 * about xmax, since it requires a conclusively locked row
+			 * version, and a concurrent update to this tuple is a conflict
+			 * of its purposes.
+			 */
+			if (HeapTupleHeaderIsSpeculative(tuple))
+			{
+				snapshot->speculativeToken =
+					HeapTupleHeaderGetSpeculativeToken(tuple);
+
+				Assert(snapshot->speculativeToken != 0);
+			}
+
 			snapshot->xmin = HeapTupleHeaderGetRawXmin(tuple);
 			/* XXX shouldn't we fall through to look at xmax? */
 			return true;		/* in insertion by other */