Use full 64-bit XID for checking if a deleted GiST page is old enough.

Otherwise, after a deleted page gets even older, it becomes unrecyclable
again. B-tree has the same problem, and has had since time immemorial,
but let's at least fix this in GiST, where this is new.

Backpatch to v12, where GiST page deletion was introduced.

Reviewed-by: Andrey Borodin
Discussion: https://www.postgresql.org/message-id/835A15A5-F1B4-4446-A711-BF48357EB602%40yandex-team.ru

1 files changed, 25 insertions, 7 deletions

diff --git a/src/backend/access/gist/gistxlog.c b/src/backend/access/gist/gistxlog.c
index 503db34d863..3b28f546465 100644
--- a/src/backend/access/gist/gistxlog.c
+++ b/src/backend/access/gist/gistxlog.c
@@ -356,8 +356,7 @@ gistRedoPageDelete(XLogReaderState *record)
 	{
 		Page		page = (Page) BufferGetPage(leafBuffer);
 
-		GistPageSetDeleteXid(page, xldata->deleteXid);
-		GistPageSetDeleted(page);
+		GistPageSetDeleted(page, xldata->deleteXid);
 
 		PageSetLSN(page, lsn);
 		MarkBufferDirty(leafBuffer);
@@ -396,8 +395,27 @@ gistRedoPageReuse(XLogReaderState *record)
 	 */
 	if (InHotStandby)
 	{
-		ResolveRecoveryConflictWithSnapshot(xlrec->latestRemovedXid,
-											xlrec->node);
+		FullTransactionId latestRemovedFullXid = xlrec->latestRemovedFullXid;
+		FullTransactionId nextFullXid = ReadNextFullTransactionId();
+		uint64		diff;
+
+		/*
+		 * ResolveRecoveryConflictWithSnapshot operates on 32-bit
+		 * TransactionIds, so truncate the logged FullTransactionId. If the
+		 * logged value is very old, so that XID wrap-around already happened
+		 * on it, there can't be any snapshots that still see it.
+		 */
+		nextFullXid = ReadNextFullTransactionId();
+		diff = U64FromFullTransactionId(nextFullXid) -
+			U64FromFullTransactionId(latestRemovedFullXid);
+		if (diff < MaxTransactionId / 2)
+		{
+			TransactionId latestRemovedXid;
+
+			latestRemovedXid = XidFromFullTransactionId(latestRemovedFullXid);
+			ResolveRecoveryConflictWithSnapshot(latestRemovedXid,
+												xlrec->node);
+		}
 	}
 }
 
@@ -554,7 +572,7 @@ gistXLogSplit(bool page_is_leaf,
  * downlink from the parent page.
  */
 XLogRecPtr
-gistXLogPageDelete(Buffer buffer, TransactionId xid,
+gistXLogPageDelete(Buffer buffer, FullTransactionId xid,
 				   Buffer parentBuffer, OffsetNumber downlinkOffset)
 {
 	gistxlogPageDelete xlrec;
@@ -578,7 +596,7 @@ gistXLogPageDelete(Buffer buffer, TransactionId xid,
  * Write XLOG record about reuse of a deleted page.
  */
 void
-gistXLogPageReuse(Relation rel, BlockNumber blkno, TransactionId latestRemovedXid)
+gistXLogPageReuse(Relation rel, BlockNumber blkno, FullTransactionId latestRemovedXid)
 {
 	gistxlogPageReuse xlrec_reuse;
 
@@ -591,7 +609,7 @@ gistXLogPageReuse(Relation rel, BlockNumber blkno, TransactionId latestRemovedXi
 	/* XLOG stuff */
 	xlrec_reuse.node = rel->rd_node;
 	xlrec_reuse.block = blkno;
-	xlrec_reuse.latestRemovedXid = latestRemovedXid;
+	xlrec_reuse.latestRemovedFullXid = latestRemovedXid;
 
 	XLogBeginInsert();
 	XLogRegisterData((char *) &xlrec_reuse, SizeOfGistxlogPageReuse);