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Fix and/or improve comments in wal.c. No code changes.

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FossilOrigin-Name: ee9991be082202c6637adb47affc777e7917be04
This commit is contained in:
drh
2010-06-23 22:00:35 +00:00
parent 346e426753
commit cd28508e58
3 changed files with 29 additions and 11 deletions
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14
src/wal.c
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@@ -31,7 +31,7 @@
** used to determine which frames within the WAL are valid and which
** are leftovers from prior checkpoints.
**
** The WAL header is 24 bytes in size and consists of the following six
** The WAL header is 32 bytes in size and consists of the following eight
** big-endian 32-bit unsigned integer values:
**
** 0: Magic number. 0x377f0682 or 0x377f0683
@@ -45,7 +45,7 @@
**
** Immediately following the wal-header are zero or more frames. Each
** frame consists of a 24-byte frame-header followed by a <page-size> bytes
** of page data. The frame-header is broken into 6 big-endian 32-bit unsigned
** of page data. The frame-header is six big-endian 32-bit unsigned
** integer values, as follows:
**
** 0: Page number.
@@ -81,6 +81,11 @@
** s1 += x[i+1] + s0;
** endfor
**
** Note that s0 and s1 are both weighted checksums using fibonacci weights
** in reverse order (the largest fibonacci weight occurs on the first element
** of the sequence being summed.) The s1 value spans all 32-bit
** terms of the sequence whereas s0 omits the final term.
**
** On a checkpoint, the WAL is first VFS.xSync-ed, then valid content of the
** WAL is transferred into the database, then the database is VFS.xSync-ed.
** The VFS.xSync operations serve as write barriers - all writes launched
@@ -1076,16 +1081,19 @@ static int walIndexRecover(Wal *pWal){
pWal->szPage = szPage;
pWal->nCkpt = sqlite3Get4byte(&aBuf[12]);
memcpy(&pWal->hdr.aSalt, &aBuf[16], 8);
/* Verify that the WAL header checksum is correct */
walChecksumBytes(pWal->hdr.bigEndCksum==SQLITE_BIGENDIAN,
aBuf, WAL_HDRSIZE-2*4, 0, pWal->hdr.aFrameCksum
);
if( pWal->hdr.aFrameCksum[0]!=sqlite3Get4byte(&aBuf[24])
|| pWal->hdr.aFrameCksum[1]!=sqlite3Get4byte(&aBuf[28])
){
goto finished;
}
/* Verify that the version number on the WAL format is one that
** are able to understand */
version = sqlite3Get4byte(&aBuf[4]);
if( version!=WAL_MAX_VERSION ){
rc = SQLITE_CANTOPEN_BKPT;