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

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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.
This commit is contained in:
Heikki Linnakangas
2014-11-04 11:35:15 +02:00
parent 404bc51cde
commit 5028f22f6e
20 changed files with 299 additions and 340 deletions
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20
src/backend/replication/slot.c
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@@ -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)));