Clean up the representation of special snapshots by including a "method

pointer" in every Snapshot struct.  This allows removal of the case-by-case
tests in HeapTupleSatisfiesVisibility, which should make it a bit faster
(I didn't try any performance tests though).  More importantly, we are no
longer violating portable C practices by assuming that small integers are
distinct from all pointer values, and HeapTupleSatisfiesDirty no longer
has a non-reentrant API involving side-effects on a global variable.

There were a couple of places calling HeapTupleSatisfiesXXX routines
directly rather than through the HeapTupleSatisfiesVisibility macro.
Since these places had to be changed anyway, I chose to make them go
through the macro for uniformity.

Along the way I renamed HeapTupleSatisfiesSnapshot to HeapTupleSatisfiesMVCC
to emphasize that it's only used with MVCC-type snapshots.  I was sorely
tempted to rename HeapTupleSatisfiesVisibility to HeapTupleSatisfiesSnapshot,
but forebore for the moment to avoid confusion and reduce the likelihood that
this patch breaks some of the pending patches.  Might want to reconsider
doing that later.

1 files changed, 52 insertions, 37 deletions

diff --git a/src/backend/utils/time/tqual.c b/src/backend/utils/time/tqual.c
index 13cc211b5db..429005a843a 100644
--- a/src/backend/utils/time/tqual.c
+++ b/src/backend/utils/time/tqual.c
@@ -1,15 +1,14 @@
 /*-------------------------------------------------------------------------
  *
  * tqual.c
- *	  POSTGRES "time" qualification code, ie, tuple visibility rules.
- *
- * The caller must hold at least a shared buffer context lock on the buffer
- * containing the tuple.  (VACUUM FULL assumes it's sufficient to have
- * exclusive lock on the containing relation, instead.)
+ *	  POSTGRES "time qualification" code, ie, tuple visibility rules.
  *
  * NOTE: all the HeapTupleSatisfies routines will update the tuple's
  * "hint" status bits if we see that the inserting or deleting transaction
- * has now committed or aborted.
+ * has now committed or aborted.  If the hint bits are changed,
+ * SetBufferCommitInfoNeedsSave is called on the passed-in buffer.
+ * The caller must hold at least a shared buffer context lock on the buffer
+ * containing the tuple.
  *
  * NOTE: must check TransactionIdIsInProgress (which looks in PGPROC array)
  * before TransactionIdDidCommit/TransactionIdDidAbort (which look in
@@ -32,7 +31,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/time/tqual.c,v 1.101 2007/01/05 22:19:47 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/time/tqual.c,v 1.102 2007/03/25 19:45:14 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -47,16 +46,21 @@
 #include "storage/procarray.h"
 #include "utils/tqual.h"
 
+
+/* Static variables representing various special snapshot semantics */
+SnapshotData SnapshotNowData = {HeapTupleSatisfiesNow};
+SnapshotData SnapshotSelfData = {HeapTupleSatisfiesSelf};
+SnapshotData SnapshotAnyData = {HeapTupleSatisfiesAny};
+SnapshotData SnapshotToastData = {HeapTupleSatisfiesToast};
+
 /*
  * These SnapshotData structs are static to simplify memory allocation
  * (see the hack in GetSnapshotData to avoid repeated malloc/free).
  */
-static SnapshotData SnapshotDirtyData;
-static SnapshotData SerializableSnapshotData;
-static SnapshotData LatestSnapshotData;
+static SnapshotData SerializableSnapshotData = {HeapTupleSatisfiesMVCC};
+static SnapshotData LatestSnapshotData = {HeapTupleSatisfiesMVCC};
 
 /* Externally visible pointers to valid snapshots: */
-Snapshot	SnapshotDirty = &SnapshotDirtyData;
 Snapshot	SerializableSnapshot = NULL;
 Snapshot	LatestSnapshot = NULL;
 
@@ -73,11 +77,11 @@ TransactionId RecentXmin = InvalidTransactionId;
 TransactionId RecentGlobalXmin = InvalidTransactionId;
 
 /* local functions */
-static bool XidInSnapshot(TransactionId xid, Snapshot snapshot);
+static bool XidInMVCCSnapshot(TransactionId xid, Snapshot snapshot);
 
 
 /*
- * HeapTupleSatisfiesItself
+ * HeapTupleSatisfiesSelf
  *		True iff heap tuple is valid "for itself".
  *
  *	Here, we consider the effects of:
@@ -101,7 +105,7 @@ static bool XidInSnapshot(TransactionId xid, Snapshot snapshot);
  *			 Xmax is not committed)))			that has not been committed
  */
 bool
-HeapTupleSatisfiesItself(HeapTupleHeader tuple, Buffer buffer)
+HeapTupleSatisfiesSelf(HeapTupleHeader tuple, Snapshot snapshot, Buffer buffer)
 {
 	if (!(tuple->t_infomask & HEAP_XMIN_COMMITTED))
 	{
@@ -278,7 +282,7 @@ HeapTupleSatisfiesItself(HeapTupleHeader tuple, Buffer buffer)
  *		that do catalog accesses.  this is unfortunate, but not critical.
  */
 bool
-HeapTupleSatisfiesNow(HeapTupleHeader tuple, Buffer buffer)
+HeapTupleSatisfiesNow(HeapTupleHeader tuple, Snapshot snapshot, Buffer buffer)
 {
 	if (!(tuple->t_infomask & HEAP_XMIN_COMMITTED))
 	{
@@ -423,6 +427,16 @@ HeapTupleSatisfiesNow(HeapTupleHeader tuple, Buffer buffer)
 }
 
 /*
+ * HeapTupleSatisfiesAny
+ *		Dummy "satisfies" routine: any tuple satisfies SnapshotAny.
+ */
+bool
+HeapTupleSatisfiesAny(HeapTupleHeader tuple, Snapshot snapshot, Buffer buffer)
+{
+	return true;
+}
+
+/*
  * HeapTupleSatisfiesToast
  *		True iff heap tuple is valid as a TOAST row.
  *
@@ -437,7 +451,8 @@ HeapTupleSatisfiesNow(HeapTupleHeader tuple, Buffer buffer)
  * table.
  */
 bool
-HeapTupleSatisfiesToast(HeapTupleHeader tuple, Buffer buffer)
+HeapTupleSatisfiesToast(HeapTupleHeader tuple, Snapshot snapshot,
+						Buffer buffer)
 {
 	if (!(tuple->t_infomask & HEAP_XMIN_COMMITTED))
 	{
@@ -676,20 +691,22 @@ HeapTupleSatisfiesUpdate(HeapTupleHeader tuple, CommandId curcid,
  *		previous commands of this transaction
  *		changes made by the current command
  *
- * This is essentially like HeapTupleSatisfiesItself as far as effects of
+ * This is essentially like HeapTupleSatisfiesSelf as far as effects of
  * the current transaction and committed/aborted xacts are concerned.
  * However, we also include the effects of other xacts still in progress.
  *
- * Returns extra information in the global variable SnapshotDirty, namely
- * xids of concurrent xacts that affected the tuple.  SnapshotDirty->xmin
- * is set to InvalidTransactionId if xmin is either committed good or
- * committed dead; or to xmin if that transaction is still in progress.
- * Similarly for SnapshotDirty->xmax.
+ * A special hack is that the passed-in snapshot struct is used as an
+ * 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.
  */
 bool
-HeapTupleSatisfiesDirty(HeapTupleHeader tuple, Buffer buffer)
+HeapTupleSatisfiesDirty(HeapTupleHeader tuple, Snapshot snapshot,
+						Buffer buffer)
 {
-	SnapshotDirty->xmin = SnapshotDirty->xmax = InvalidTransactionId;
+	snapshot->xmin = snapshot->xmax = InvalidTransactionId;
 
 	if (!(tuple->t_infomask & HEAP_XMIN_COMMITTED))
 	{
@@ -759,7 +776,7 @@ HeapTupleSatisfiesDirty(HeapTupleHeader tuple, Buffer buffer)
 		}
 		else if (TransactionIdIsInProgress(HeapTupleHeaderGetXmin(tuple)))
 		{
-			SnapshotDirty->xmin = HeapTupleHeaderGetXmin(tuple);
+			snapshot->xmin = HeapTupleHeaderGetXmin(tuple);
 			/* XXX shouldn't we fall through to look at xmax? */
 			return true;		/* in insertion by other */
 		}
@@ -805,7 +822,7 @@ HeapTupleSatisfiesDirty(HeapTupleHeader tuple, Buffer buffer)
 
 	if (TransactionIdIsInProgress(HeapTupleHeaderGetXmax(tuple)))
 	{
-		SnapshotDirty->xmax = HeapTupleHeaderGetXmax(tuple);
+		snapshot->xmax = HeapTupleHeaderGetXmax(tuple);
 		return true;
 	}
 
@@ -832,8 +849,8 @@ HeapTupleSatisfiesDirty(HeapTupleHeader tuple, Buffer buffer)
 }
 
 /*
- * HeapTupleSatisfiesSnapshot
- *		True iff heap tuple is valid for the given snapshot.
+ * HeapTupleSatisfiesMVCC
+ *		True iff heap tuple is valid for the given MVCC snapshot.
  *
  *	Here, we consider the effects of:
  *		all transactions committed as of the time of the given snapshot
@@ -853,8 +870,8 @@ HeapTupleSatisfiesDirty(HeapTupleHeader tuple, Buffer buffer)
  * can't see it.)
  */
 bool
-HeapTupleSatisfiesSnapshot(HeapTupleHeader tuple, Snapshot snapshot,
-						   Buffer buffer)
+HeapTupleSatisfiesMVCC(HeapTupleHeader tuple, Snapshot snapshot,
+					   Buffer buffer)
 {
 	if (!(tuple->t_infomask & HEAP_XMIN_COMMITTED))
 	{
@@ -949,7 +966,7 @@ HeapTupleSatisfiesSnapshot(HeapTupleHeader tuple, Snapshot snapshot,
 	 * By here, the inserting transaction has committed - have to check
 	 * when...
 	 */
-	if (XidInSnapshot(HeapTupleHeaderGetXmin(tuple), snapshot))
+	if (XidInMVCCSnapshot(HeapTupleHeaderGetXmin(tuple), snapshot))
 		return false;			/* treat as still in progress */
 
 	if (tuple->t_infomask & HEAP_XMAX_INVALID)	/* xid invalid or aborted */
@@ -994,7 +1011,7 @@ HeapTupleSatisfiesSnapshot(HeapTupleHeader tuple, Snapshot snapshot,
 	/*
 	 * OK, the deleting transaction committed too ... but when?
 	 */
-	if (XidInSnapshot(HeapTupleHeaderGetXmax(tuple), snapshot))
+	if (XidInMVCCSnapshot(HeapTupleHeaderGetXmax(tuple), snapshot))
 		return true;			/* treat as still in progress */
 
 	return false;
@@ -1241,8 +1258,6 @@ GetLatestSnapshot(void)
  *		Copy the given snapshot.
  *
  * The copy is palloc'd in the current memory context.
- *
- * Note that this will not work on "special" snapshots.
  */
 Snapshot
 CopySnapshot(Snapshot snapshot)
@@ -1290,7 +1305,7 @@ CopySnapshot(Snapshot snapshot)
  * This is currently identical to pfree, but is provided for cleanliness.
  *
  * Do *not* apply this to the results of GetTransactionSnapshot or
- * GetLatestSnapshot.
+ * GetLatestSnapshot, since those are just static structs.
  */
 void
 FreeSnapshot(Snapshot snapshot)
@@ -1316,7 +1331,7 @@ FreeXactSnapshot(void)
 }
 
 /*
- * XidInSnapshot
+ * XidInMVCCSnapshot
  *		Is the given XID still-in-progress according to the snapshot?
  *
  * Note: GetSnapshotData never stores either top xid or subxids of our own
@@ -1325,7 +1340,7 @@ FreeXactSnapshot(void)
  * apply this for known-committed XIDs.
  */
 static bool
-XidInSnapshot(TransactionId xid, Snapshot snapshot)
+XidInMVCCSnapshot(TransactionId xid, Snapshot snapshot)
 {
 	uint32		i;