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, 10 insertions, 10 deletions

diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index f355f13d293..2c3ea555d09 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -993,7 +993,7 @@ SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel)
 	}
 
 	cp.magic = SLOT_MAGIC;
-	INIT_CRC32(cp.checksum);
+	INIT_CRC32C(cp.checksum);
 	cp.version = 1;
 	cp.length = ReplicationSlotOnDiskDynamicSize;
 
@@ -1003,9 +1003,9 @@ SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel)
 
 	SpinLockRelease(&slot->mutex);
 
-	COMP_CRC32(cp.checksum,
-			   (char *) (&cp) + ReplicationSlotOnDiskConstantSize,
-			   ReplicationSlotOnDiskDynamicSize);
+	COMP_CRC32C(cp.checksum,
+				(char *) (&cp) + ReplicationSlotOnDiskConstantSize,
+				ReplicationSlotOnDiskDynamicSize);
 
 	if ((write(fd, &cp, sizeof(cp))) != sizeof(cp))
 	{
@@ -1181,13 +1181,13 @@ RestoreSlotFromDisk(const char *name)
 
 	CloseTransientFile(fd);
 
-	/* now verify the CRC32 */
-	INIT_CRC32(checksum);
-	COMP_CRC32(checksum,
-			   (char *) &cp + ReplicationSlotOnDiskConstantSize,
-			   ReplicationSlotOnDiskDynamicSize);
+	/* now verify the CRC */
+	INIT_CRC32C(checksum);
+	COMP_CRC32C(checksum,
+				(char *) &cp + ReplicationSlotOnDiskConstantSize,
+				ReplicationSlotOnDiskDynamicSize);
 
-	if (!EQ_CRC32(checksum, cp.checksum))
+	if (!EQ_CRC32C(checksum, cp.checksum))
 		ereport(PANIC,
 				(errmsg("replication slot file %s: checksum mismatch, is %u, should be %u",
 						path, checksum, cp.checksum)));