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Update header comments in wal.c to correctly describe the WAL file format.

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Update the locking region offsets in os_unix.c and os_win.c and add assert()
statement to verify that the locking region offsets are correct.

FossilOrigin-Name: 40030c0739f821ea8ee188c28c579507f10448bc
This commit is contained in:
drh
2010-05-25 13:40:03 +00:00
parent ca6b5baba4
commit 1b78eaf0ba
5 changed files with 42 additions and 16 deletions
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24
src/wal.c
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@@ -34,7 +34,7 @@
** The WAL header is 24 bytes in size and consists of the following six
** big-endian 32-bit unsigned integer values:
**
** 0: Magic number. 0x377f0682 (big endian)
** 0: Magic number. 0x377f0682 or 0x377f0683
** 4: File format version. Currently 3007000
** 8: Database page size. Example: 1024
** 12: Checkpoint sequence number
@@ -61,9 +61,13 @@
** salt values in the wal-header
**
** (2) The checksum values in the final 8 bytes of the frame-header
** exactly match the checksum computed consecutively on
** (a) the first 16 bytes of the frame-header, and
** (b) the frame data.
** exactly match the checksum computed consecutively on the
** WAL header and the first 8 bytes and the content of all frames
** up to and including the current frame.
**
** The checksum is computed using 32-bit big-endian integers if the
** magic number in the first 4 bytes of the WAL is 0x377f0683 and it
** is computed using little-endian if the magic number is 0x377f0682.
**
** 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.
@@ -947,6 +951,18 @@ int sqlite3WalOpen(
assert( zDbName && zDbName[0] );
assert( pDbFd );
/* In the amalgamation, the os_unix.c and os_win.c source files come before
** this source file. Verify that the #defines of the locking byte offsets
** in os_unix.c and os_win.c agree with the WALINDEX_LOCK_OFFSET value.
*/
#ifdef WIN_SHM_BASE
assert( WIN_SHM_BASE==WALINDEX_LOCK_OFFSET );
#endif
#ifdef UNIX_SHM_BASE
assert( UNIX_SHM_BASE==WALINDEX_LOCK_OFFSET );
#endif
/* Allocate an instance of struct Wal to return. */
*ppWal = 0;
nWal = sqlite3Strlen30(zDbName) + 5;