Avoid repeating loads of frozen ID values.

Repeating loads of inplace-updated fields tends to cause bugs like the
one from the previous commit.  While there's no bug to fix in these code
sites, adopt the load-once style.  This improves the chance of future
copy/paste finding the safe style.

Discussion: https://postgr.es/m/20240423003956.e7.nmisch@google.com

2 files changed, 16 insertions, 10 deletions

diff --git a/src/backend/commands/cluster.c b/src/backend/commands/cluster.c
index c04886c4090..78f96789b0e 100644
--- a/src/backend/commands/cluster.c
+++ b/src/backend/commands/cluster.c
@@ -919,18 +919,24 @@ copy_table_data(Oid OIDNewHeap, Oid OIDOldHeap, Oid OIDOldIndex, bool verbose,
 	 * FreezeXid will become the table's new relfrozenxid, and that mustn't go
 	 * backwards, so take the max.
 	 */
-	if (TransactionIdIsValid(OldHeap->rd_rel->relfrozenxid) &&
-		TransactionIdPrecedes(cutoffs.FreezeLimit,
-							  OldHeap->rd_rel->relfrozenxid))
-		cutoffs.FreezeLimit = OldHeap->rd_rel->relfrozenxid;
+	{
+		TransactionId relfrozenxid = OldHeap->rd_rel->relfrozenxid;
+
+		if (TransactionIdIsValid(relfrozenxid) &&
+			TransactionIdPrecedes(cutoffs.FreezeLimit, relfrozenxid))
+			cutoffs.FreezeLimit = relfrozenxid;
+	}
 
 	/*
 	 * MultiXactCutoff, similarly, shouldn't go backwards either.
 	 */
-	if (MultiXactIdIsValid(OldHeap->rd_rel->relminmxid) &&
-		MultiXactIdPrecedes(cutoffs.MultiXactCutoff,
-							OldHeap->rd_rel->relminmxid))
-		cutoffs.MultiXactCutoff = OldHeap->rd_rel->relminmxid;
+	{
+		MultiXactId relminmxid = OldHeap->rd_rel->relminmxid;
+
+		if (MultiXactIdIsValid(relminmxid) &&
+			MultiXactIdPrecedes(cutoffs.MultiXactCutoff, relminmxid))
+			cutoffs.MultiXactCutoff = relminmxid;
+	}
 
 	/*
 	 * Decide whether to use an indexscan or seqscan-and-optional-sort to scan
diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index a63a71c984d..521ee74586a 100644
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -1200,7 +1200,7 @@ vacuum_get_cutoffs(Relation rel, const VacuumParams *params,
 	aggressiveXIDCutoff = nextXID - freeze_table_age;
 	if (!TransactionIdIsNormal(aggressiveXIDCutoff))
 		aggressiveXIDCutoff = FirstNormalTransactionId;
-	if (TransactionIdPrecedesOrEquals(rel->rd_rel->relfrozenxid,
+	if (TransactionIdPrecedesOrEquals(cutoffs->relfrozenxid,
 									  aggressiveXIDCutoff))
 		return true;
 
@@ -1221,7 +1221,7 @@ vacuum_get_cutoffs(Relation rel, const VacuumParams *params,
 	aggressiveMXIDCutoff = nextMXID - multixact_freeze_table_age;
 	if (aggressiveMXIDCutoff < FirstMultiXactId)
 		aggressiveMXIDCutoff = FirstMultiXactId;
-	if (MultiXactIdPrecedesOrEquals(rel->rd_rel->relminmxid,
+	if (MultiXactIdPrecedesOrEquals(cutoffs->relminmxid,
 									aggressiveMXIDCutoff))
 		return true;