From: drh <drh@noemail.net>
Date: Wed, 23 Jun 2010 22:00:35 +0000 (+0000)
Subject: Fix and/or improve comments in wal.c.  No code changes.
X-Git-Tag: version-3.7.2~241
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=cd28508e5876eb173d4cdcdbd5104f6b497a32bf;p=thirdparty%2Fsqlite.git

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

FossilOrigin-Name: ee9991be082202c6637adb47affc777e7917be04
---

diff --git a/manifest b/manifest
index 42a42ac8b9..3396c68a2c 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,8 @@
-C Add\stest\scase\sfor\sSQLITE_FULL\serrors\sto\spagerfault.test.\sRemove\sa\sNEVER\smacro\sin\spager.c\sthat\sthis\shits.
-D 2010-06-23T19:27:36
+-----BEGIN PGP SIGNED MESSAGE-----
+Hash: SHA1
+
+C Fix\sand/or\simprove\scomments\sin\swal.c.\s\sNo\scode\schanges.
+D 2010-06-23T22:00:36
 F Makefile.arm-wince-mingw32ce-gcc fcd5e9cd67fe88836360bb4f9ef4cb7f8e2fb5a0
 F Makefile.in a5cad1f8f3e021356bfcc6c77dc16f6f1952bbc3
 F Makefile.linux-gcc d53183f4aa6a9192d249731c90dbdffbd2c68654
@@ -226,7 +229,7 @@ F src/vdbeblob.c 258a6010ba7a82b72b327fb24c55790655689256
 F src/vdbemem.c 2a82f455f6ca6f78b59fb312f96054c04ae0ead1
 F src/vdbetrace.c 864cef96919323482ebd9986f2132435115e9cc2
 F src/vtab.c a0f8a40274e4261696ef57aa806de2776ab72cda
-F src/wal.c 563b7030efc55fe1ef105bd865876f2bf74f281b
+F src/wal.c 51b5d2259d86a26125007d3d788da5a2a2715b1a
 F src/wal.h 4ace25262452d17e7d3ec970c89ee17794004008
 F src/walker.c 3112bb3afe1d85dc52317cb1d752055e9a781f8f
 F src/where.c 1c895bef33d0dfc7ed90fb1f74120435d210ea56
@@ -825,7 +828,14 @@ F tool/speedtest2.tcl ee2149167303ba8e95af97873c575c3e0fab58ff
 F tool/speedtest8.c 2902c46588c40b55661e471d7a86e4dd71a18224
 F tool/speedtest8inst1.c 293327bc76823f473684d589a8160bde1f52c14e
 F tool/vdbe-compress.tcl d70ea6d8a19e3571d7ab8c9b75cba86d1173ff0f
-P 1727a81fed65bebfea43e0bda271584096d82785
-R 7a852c823aafd5a6b2955a7dd5f8280a
-U dan
-Z 7f4e2d2171817ab7dccd91b04d1a7459
+P 3e9680c4c18140d083b24e05a21ea6792aef2487
+R 128d792d7f9b9a40582f4d46c120cca4
+U drh
+Z 369983deae2c52862083f493477e4ceb
+-----BEGIN PGP SIGNATURE-----
+Version: GnuPG v1.4.6 (GNU/Linux)
+
+iD8DBQFMIoQHoxKgR168RlERAkTMAJ4y6IEC74XLF+DMxIuBS7Lmcv3IqQCeJXdd
+wPN5UVQx6y4hhnn2sGwnj/w=
+=O5UN
+-----END PGP SIGNATURE-----
diff --git a/manifest.uuid b/manifest.uuid
index a33a53c493..cd54b0bdbc 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-3e9680c4c18140d083b24e05a21ea6792aef2487
\ No newline at end of file
+ee9991be082202c6637adb47affc777e7917be04
\ No newline at end of file
diff --git a/src/wal.c b/src/wal.c
index 83dd758378..bbd2546eb5 100644
--- a/src/wal.c
+++ b/src/wal.c
@@ -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;