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

12
src/backend/access/transam/xlogreader.c
View File

@ -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",