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, 16 insertions, 6 deletions

diff --git a/src/include/utils/snapshot.h b/src/include/utils/snapshot.h
index 26fb2573c7..a734bf0075 100644
--- a/src/include/utils/snapshot.h
+++ b/src/include/utils/snapshot.h
@@ -69,31 +69,41 @@ typedef struct SnapshotData
 	 * progress, unless the snapshot was taken during recovery in which case
 	 * it's empty. For historic MVCC snapshots, the meaning is inverted, i.e.
 	 * it contains *committed* transactions between xmin and xmax.
+	 *
+	 * note: all ids in xip[] satisfy xmin <= xip[i] < xmax
 	 */
 	TransactionId *xip;
 	uint32		xcnt;			/* # of xact ids in xip[] */
-	/* note: all ids in xip[] satisfy xmin <= xip[i] < xmax */
-	int32		subxcnt;		/* # of xact ids in subxip[] */
 
 	/*
 	 * For non-historic MVCC snapshots, this contains subxact IDs that are in
 	 * progress (and other transactions that are in progress if taken during
 	 * recovery). For historic snapshot it contains *all* xids assigned to the
 	 * replayed transaction, including the toplevel xid.
+	 *
+	 * note: all ids in subxip[] are >= xmin, but we don't bother filtering
+	 * out any that are >= xmax
 	 */
 	TransactionId *subxip;
+	int32		subxcnt;		/* # of xact ids in subxip[] */
 	bool		suboverflowed;	/* has the subxip array overflowed? */
+
 	bool		takenDuringRecovery;	/* recovery-shaped snapshot? */
 	bool		copied;			/* false if it's a static snapshot */
 
+	CommandId	curcid;			/* in my xact, CID < curcid are visible */
+
 	/*
-	 * note: all ids in subxip[] are >= xmin, but we don't bother filtering
-	 * out any that are >= xmax
+	 * An extra return value for HeapTupleSatisfiesDirty, not used in MVCC
+	 * snapshots.
+	 */
+	uint32		speculativeToken;
+
+	/*
+	 * Book-keeping information, used by the snapshot manager
 	 */
-	CommandId	curcid;			/* in my xact, CID < curcid are visible */
 	uint32		active_count;	/* refcount on ActiveSnapshot stack */
 	uint32		regd_count;		/* refcount on RegisteredSnapshots */
-
 	pairingheap_node ph_node;	/* link in the RegisteredSnapshots heap */
 } SnapshotData;