database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-07-02 09:02:37 +03:00
Code Activity

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

Browse Source 
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
Download Patch File Download Diff File Expand all files Collapse all files

16
src/backend/utils/cache/relmapper.c vendored
View File

@ -84,7 +84,7 @@ typedef struct RelMapFile
int32 magic; /* always RELMAPPER_FILEMAGIC */
int32 num_mappings; /* number of valid RelMapping entries */
RelMapping mappings[MAX_MAPPINGS];
int32 crc; /* CRC of all above */
pg_crc32 crc; /* CRC of all above */
int32 pad; /* to make the struct size be 512 exactly */
} RelMapFile;
@ -673,11 +673,11 @@ load_relmap_file(bool shared)
mapfilename)));
/* verify the CRC */
INIT_CRC32(crc);
COMP_CRC32(crc, (char *) map, offsetof(RelMapFile, crc));
FIN_CRC32(crc);
INIT_CRC32C(crc);
COMP_CRC32C(crc, (char *) map, offsetof(RelMapFile, crc));
FIN_CRC32C(crc);
if (!EQ_CRC32(crc, map->crc))
if (!EQ_CRC32C(crc, map->crc))
ereport(FATAL,
(errmsg("relation mapping file \"%s\" contains incorrect checksum",
mapfilename)));
@ -719,9 +719,9 @@ write_relmap_file(bool shared, RelMapFile *newmap,
if (newmap->num_mappings < 0 || newmap->num_mappings > MAX_MAPPINGS)
elog(ERROR, "attempt to write bogus relation mapping");
INIT_CRC32(newmap->crc);
COMP_CRC32(newmap->crc, (char *) newmap, offsetof(RelMapFile, crc));
FIN_CRC32(newmap->crc);
INIT_CRC32C(newmap->crc);
COMP_CRC32C(newmap->crc, (char *) newmap, offsetof(RelMapFile, crc));
FIN_CRC32C(newmap->crc);
/*
* Open the target file. We prefer to do this before entering the