Increase width of RelFileNumbers from 32 bits to 56 bits.

RelFileNumbers are now assigned using a separate counter, instead of
being assigned from the OID counter. This counter never wraps around:
if all 2^56 possible RelFileNumbers are used, an internal error
occurs. As the cluster is limited to 2^64 total bytes of WAL, this
limitation should not cause a problem in practice.

If the counter were 64 bits wide rather than 56 bits wide, we would
need to increase the width of the BufferTag, which might adversely
impact buffer lookup performance. Also, this lets us use bigint for
pg_class.relfilenode and other places where these values are exposed
at the SQL level without worrying about overflow.

This should remove the need to keep "tombstone" files around until
the next checkpoint when relations are removed. We do that to keep
RelFileNumbers from being recycled, but now that won't happen
anyway. However, this patch doesn't actually change anything in
this area; it just makes it possible for a future patch to do so.

Dilip Kumar, based on an idea from Andres Freund, who also reviewed
some earlier versions of the patch. Further review and some
wordsmithing by me. Also reviewed at various points by Ashutosh
Sharma, Vignesh C, Amul Sul, Álvaro Herrera, and Tom Lane.

Discussion: http://postgr.es/m/CA+Tgmobp7+7kmi4gkq7Y+4AM9fTvL+O1oQ4-5gFTT+6Ng-dQ=g@mail.gmail.com

1 files changed, 16 insertions, 5 deletions

diff --git a/src/backend/access/rmgrdesc/xlogdesc.c b/src/backend/access/rmgrdesc/xlogdesc.c
index 3fd7185f217..84a826bf49c 100644
--- a/src/backend/access/rmgrdesc/xlogdesc.c
+++ b/src/backend/access/rmgrdesc/xlogdesc.c
@@ -45,8 +45,8 @@ xlog_desc(StringInfo buf, XLogReaderState *record)
 		CheckPoint *checkpoint = (CheckPoint *) rec;
 
 		appendStringInfo(buf, "redo %X/%X; "
-						 "tli %u; prev tli %u; fpw %s; xid %u:%u; oid %u; multi %u; offset %u; "
-						 "oldest xid %u in DB %u; oldest multi %u in DB %u; "
+						 "tli %u; prev tli %u; fpw %s; xid %u:%u; relfilenumber " UINT64_FORMAT ";oid %u; "
+						 "multi %u; offset %u; oldest xid %u in DB %u; oldest multi %u in DB %u; "
 						 "oldest/newest commit timestamp xid: %u/%u; "
 						 "oldest running xid %u; %s",
 						 LSN_FORMAT_ARGS(checkpoint->redo),
@@ -55,6 +55,7 @@ xlog_desc(StringInfo buf, XLogReaderState *record)
 						 checkpoint->fullPageWrites ? "true" : "false",
 						 EpochFromFullTransactionId(checkpoint->nextXid),
 						 XidFromFullTransactionId(checkpoint->nextXid),
+						 checkpoint->nextRelFileNumber,
 						 checkpoint->nextOid,
 						 checkpoint->nextMulti,
 						 checkpoint->nextMultiOffset,
@@ -74,6 +75,13 @@ xlog_desc(StringInfo buf, XLogReaderState *record)
 		memcpy(&nextOid, rec, sizeof(Oid));
 		appendStringInfo(buf, "%u", nextOid);
 	}
+	else if (info == XLOG_NEXT_RELFILENUMBER)
+	{
+		RelFileNumber nextRelFileNumber;
+
+		memcpy(&nextRelFileNumber, rec, sizeof(RelFileNumber));
+		appendStringInfo(buf, UINT64_FORMAT, nextRelFileNumber);
+	}
 	else if (info == XLOG_RESTORE_POINT)
 	{
 		xl_restore_point *xlrec = (xl_restore_point *) rec;
@@ -169,6 +177,9 @@ xlog_identify(uint8 info)
 		case XLOG_NEXTOID:
 			id = "NEXTOID";
 			break;
+		case XLOG_NEXT_RELFILENUMBER:
+			id = "NEXT_RELFILENUMBER";
+			break;
 		case XLOG_SWITCH:
 			id = "SWITCH";
 			break;
@@ -237,7 +248,7 @@ XLogRecGetBlockRefInfo(XLogReaderState *record, bool pretty,
 				appendStringInfoChar(buf, ' ');
 
 			appendStringInfo(buf,
-							 "blkref #%d: rel %u/%u/%u fork %s blk %u",
+							 "blkref #%d: rel %u/%u/" UINT64_FORMAT " fork %s blk %u",
 							 block_id,
 							 rlocator.spcOid, rlocator.dbOid, rlocator.relNumber,
 							 forkNames[forknum],
@@ -297,7 +308,7 @@ XLogRecGetBlockRefInfo(XLogReaderState *record, bool pretty,
 			if (forknum != MAIN_FORKNUM)
 			{
 				appendStringInfo(buf,
-								 ", blkref #%d: rel %u/%u/%u fork %s blk %u",
+								 ", blkref #%d: rel %u/%u/" UINT64_FORMAT " fork %s blk %u",
 								 block_id,
 								 rlocator.spcOid, rlocator.dbOid, rlocator.relNumber,
 								 forkNames[forknum],
@@ -306,7 +317,7 @@ XLogRecGetBlockRefInfo(XLogReaderState *record, bool pretty,
 			else
 			{
 				appendStringInfo(buf,
-								 ", blkref #%d: rel %u/%u/%u blk %u",
+								 ", blkref #%d: rel %u/%u/" UINT64_FORMAT " blk %u",
 								 block_id,
 								 rlocator.spcOid, rlocator.dbOid, rlocator.relNumber,
 								 blk);