ReadNewTransactionId() -> ReadNextTransactionId().

The new name conveys the effect better, is more consistent with similar
functions ReadNextMultiXactId(), ReadNextFullTransactionId(), and
matches the name of the variable that it reads.

Reported-by: Peter Geoghegan <pg@bowt.ie>
Discussion: https://postgr.es/m/CAH2-WzmVR4SakBXQUdhhPpMf1aYvZCnna5%3DHKa7DAgEmBAg%2B8g%40mail.gmail.com

src/backend/access/gin/ginvacuum.c

@@ -189,7 +189,7 @@ ginDeletePage(GinVacuumState *gvs, BlockNumber deleteBlkno, BlockNumber leftBlkn
 	 * address.
 	 */
 	GinPageSetDeleted(page);
-	GinPageSetDeleteXid(page, ReadNewTransactionId());
+	GinPageSetDeleteXid(page, ReadNextTransactionId());
 
 	MarkBufferDirty(pBuffer);
 	MarkBufferDirty(lBuffer);

src/backend/access/nbtree/nbtpage.c

@@ -2266,7 +2266,7 @@ _bt_mark_page_halfdead(Relation rel, Buffer leafbuf, BTStack stack)
  *
  * We maintain *oldestBtpoXact for pages that are deleted by the current
  * VACUUM operation here.  This must be handled here because we conservatively
- * assume that there needs to be a new call to ReadNewTransactionId() each
+ * assume that there needs to be a new call to ReadNextTransactionId() each
  * time a page gets deleted.  See comments about the underlying assumption
  * below.
  *
@@ -2559,7 +2559,7 @@ _bt_unlink_halfdead_page(Relation rel, Buffer leafbuf, BlockNumber scanblkno,
 	 * Mark the page itself deleted.  It can be recycled when all current
 	 * transactions are gone.  Storing GetTopTransactionId() would work, but
 	 * we're in VACUUM and would not otherwise have an XID.  Having already
-	 * updated links to the target, ReadNewTransactionId() suffices as an
+	 * updated links to the target, ReadNextTransactionId() suffices as an
 	 * upper bound.  Any scan having retained a now-stale link is advertising
 	 * in its PGPROC an xmin less than or equal to the value we read here.  It
 	 * will continue to do so, holding back the xmin horizon, for the duration
@@ -2570,7 +2570,7 @@ _bt_unlink_halfdead_page(Relation rel, Buffer leafbuf, BlockNumber scanblkno,
 	Assert(P_ISHALFDEAD(opaque) || !P_ISLEAF(opaque));
 	opaque->btpo_flags &= ~BTP_HALF_DEAD;
 	opaque->btpo_flags |= BTP_DELETED;
-	opaque->btpo.xact = ReadNewTransactionId();
+	opaque->btpo.xact = ReadNextTransactionId();
 
 	/*
 	 * Remove the remaining tuples on the page.  This keeps things simple for

src/backend/access/transam/commit_ts.c

@@ -733,7 +733,7 @@ ActivateCommitTs(void)
 	if (ShmemVariableCache->oldestCommitTsXid == InvalidTransactionId)
 	{
 		ShmemVariableCache->oldestCommitTsXid =
-			ShmemVariableCache->newestCommitTsXid = ReadNewTransactionId();
+			ShmemVariableCache->newestCommitTsXid = ReadNextTransactionId();
 	}
 	LWLockRelease(CommitTsLock);
 

src/backend/access/transam/xact.c

@@ -548,7 +548,7 @@ GetStableLatestTransactionId(void)
 		lxid = MyProc->lxid;
 		stablexid = GetTopTransactionIdIfAny();
 		if (!TransactionIdIsValid(stablexid))
-			stablexid = ReadNewTransactionId();
+			stablexid = ReadNextTransactionId();
 	}
 
 	Assert(TransactionIdIsValid(stablexid));

src/backend/commands/vacuum.c

@@ -1014,7 +1014,7 @@ vacuum_set_xid_limits(Relation rel,
 	 * autovacuum_freeze_max_age / 2 XIDs old), complain and force a minimum
 	 * freeze age of zero.
 	 */
-	safeLimit = ReadNewTransactionId() - autovacuum_freeze_max_age;
+	safeLimit = ReadNextTransactionId() - autovacuum_freeze_max_age;
 	if (!TransactionIdIsNormal(safeLimit))
 		safeLimit = FirstNormalTransactionId;
 
@@ -1097,7 +1097,7 @@ vacuum_set_xid_limits(Relation rel,
 		 * Compute XID limit causing a full-table vacuum, being careful not to
 		 * generate a "permanent" XID.
 		 */
-		limit = ReadNewTransactionId() - freezetable;
+		limit = ReadNextTransactionId() - freezetable;
 		if (!TransactionIdIsNormal(limit))
 			limit = FirstNormalTransactionId;
 
@@ -1314,7 +1314,7 @@ vac_update_relstats(Relation relation,
 	if (TransactionIdIsNormal(frozenxid) &&
 		pgcform->relfrozenxid != frozenxid &&
 		(TransactionIdPrecedes(pgcform->relfrozenxid, frozenxid) ||
-		 TransactionIdPrecedes(ReadNewTransactionId(),
+		 TransactionIdPrecedes(ReadNextTransactionId(),
 							   pgcform->relfrozenxid)))
 	{
 		pgcform->relfrozenxid = frozenxid;
@@ -1401,7 +1401,7 @@ vac_update_datfrozenxid(void)
 	 * validly see during the scan.  These are conservative values, but it's
 	 * not really worth trying to be more exact.
 	 */
-	lastSaneFrozenXid = ReadNewTransactionId();
+	lastSaneFrozenXid = ReadNextTransactionId();
 	lastSaneMinMulti = ReadNextMultiXactId();
 
 	/*
@@ -1577,7 +1577,7 @@ vac_truncate_clog(TransactionId frozenXID,
 				  TransactionId lastSaneFrozenXid,
 				  MultiXactId lastSaneMinMulti)
 {
-	TransactionId nextXID = ReadNewTransactionId();
+	TransactionId nextXID = ReadNextTransactionId();
 	Relation	relation;
 	TableScanDesc scan;
 	HeapTuple	tuple;

src/backend/postmaster/autovacuum.c

@@ -1190,7 +1190,7 @@ do_start_worker(void)
 	 * pass without forcing a vacuum.  (This limit can be tightened for
 	 * particular tables, but not loosened.)
 	 */
-	recentXid = ReadNewTransactionId();
+	recentXid = ReadNextTransactionId();
 	xidForceLimit = recentXid - autovacuum_freeze_max_age;
 	/* ensure it's a "normal" XID, else TransactionIdPrecedes misbehaves */
 	/* this can cause the limit to go backwards by 3, but that's OK */
@@ -1709,7 +1709,7 @@ AutoVacWorkerMain(int argc, char *argv[])
 			pg_usleep(PostAuthDelay * 1000000L);
 
 		/* And do an appropriate amount of work */
-		recentXid = ReadNewTransactionId();
+		recentXid = ReadNextTransactionId();
 		recentMulti = ReadNextMultiXactId();
 		do_autovacuum();
 	}

src/include/access/transam.h

@@ -305,7 +305,7 @@ extern void AssertTransactionIdInAllowableRange(TransactionId xid);
  * For callers that just need the XID part of the next transaction ID.
  */
 static inline TransactionId
-ReadNewTransactionId(void)
+ReadNextTransactionId(void)
 {
 	return XidFromFullTransactionId(ReadNextFullTransactionId());
 }