Switch to CRC-32C in WAL and other places.

The old algorithm was found to not be the usual CRC-32 algorithm, used by
Ethernet et al. We were using a non-reflected lookup table with code meant
for a reflected lookup table. That's a strange combination that AFAICS does
not correspond to any bit-wise CRC calculation, which makes it difficult to
reason about its properties. Although it has worked well in practice, seems
safer to use a well-known algorithm.

Since we're changing the algorithm anyway, we might as well choose a
different polynomial. The Castagnoli polynomial has better error-correcting
properties than the traditional CRC-32 polynomial, even if we had
implemented it correctly. Another reason for picking that is that some new
CPUs have hardware support for calculating CRC-32C, but not CRC-32, let
alone our strange variant of it. This patch doesn't add any support for such
hardware, but a future patch could now do that.

The old algorithm is kept around for tsquery and pg_trgm, which use the
values in indexes that need to remain compatible so that pg_upgrade works.
While we're at it, share the old lookup table for CRC-32 calculation
between hstore, ltree and core. They all use the same table, so might as
well.

1 files changed, 6 insertions, 6 deletions

diff --git a/src/backend/access/transam/xlogreader.c b/src/backend/access/transam/xlogreader.c
index f06daa2638f..da7ed92941c 100644
--- a/src/backend/access/transam/xlogreader.c
+++ b/src/backend/access/transam/xlogreader.c
@@ -684,8 +684,8 @@ ValidXLogRecord(XLogReaderState *state, XLogRecord *record, XLogRecPtr recptr)
 		return false;
 	}
 	remaining -= SizeOfXLogRecord + len;
-	INIT_CRC32(crc);
-	COMP_CRC32(crc, XLogRecGetData(record), len);
+	INIT_CRC32C(crc);
+	COMP_CRC32C(crc, XLogRecGetData(record), len);
 
 	/* Add in the backup blocks, if any */
 	blk = (char *) XLogRecGetData(record) + len;
@@ -722,7 +722,7 @@ ValidXLogRecord(XLogReaderState *state, XLogRecord *record, XLogRecPtr recptr)
 			return false;
 		}
 		remaining -= blen;
-		COMP_CRC32(crc, blk, blen);
+		COMP_CRC32C(crc, blk, blen);
 		blk += blen;
 	}
 
@@ -736,10 +736,10 @@ ValidXLogRecord(XLogReaderState *state, XLogRecord *record, XLogRecPtr recptr)
 	}
 
 	/* Finally include the record header */
-	COMP_CRC32(crc, (char *) record, offsetof(XLogRecord, xl_crc));
-	FIN_CRC32(crc);
+	COMP_CRC32C(crc, (char *) record, offsetof(XLogRecord, xl_crc));
+	FIN_CRC32C(crc);
 
-	if (!EQ_CRC32(record->xl_crc, crc))
+	if (!EQ_CRC32C(record->xl_crc, crc))
 	{
 		report_invalid_record(state,
 			   "incorrect resource manager data checksum in record at %X/%X",