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Comment:Correct details in the description of the SHM file format.
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SHA3-256:d40d77faa2d0a9a6495952dc2a0258e855e9ae6447db51b71629e00bca7a8683
User & Date: drh 2018-04-12 14:09:28
Context
2018-04-12
14:47
Tweaks to the whynotgit.html page. check-in: 149486cfb5 user: drh tags: trunk
14:09
Correct details in the description of the SHM file format. check-in: d40d77faa2 user: drh tags: trunk
2018-04-11
17:10
Fix a typo in the whynotgit.html document. check-in: b4af616809 user: drh tags: trunk
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Changes to pages/walformat.in.

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<tr><th>Bytes<th>Description
<tr><td valign=top>0..47</td><td>First copy of the WAL Index Information</td>
<tr><td valign=top>48..95</td><td>Second copy of the WAL Index Information</td>
<tr><td valign=top>96..135</td><td>Checkpoint Information and Locks</td>
</table>
</center>

<p>Individual fields of the shm header are all unsigned integers

in the native byte-order of the host machine.


The size of integers may be 8, 16, 32, or 64 bits.
A detailed breakout of the individual fields of the shm header
follows:

<center>
<i>WAL-Index Header Details</i><br>
<table width="80%" border=1>
................................................................................
<tr>
<td>24..31</td><td>aFrameCksum</td>
<td>Checksum of the last frame in the WAL file.
</tr>
<tr>
<td>32..39</td><td>aSalt</td>
<td>The two salt value copied from the WAL file header.



</tr>
<tr>
<td>40..47</td><td>aCksum</td>
<td>A checksum over bytes 0 through 39 of this header.
</tr>
<tr>
<td>48..95</td><td>&nbsp;</td>







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<tr><th>Bytes<th>Description
<tr><td valign=top>0..47</td><td>First copy of the WAL Index Information</td>
<tr><td valign=top>48..95</td><td>Second copy of the WAL Index Information</td>
<tr><td valign=top>96..135</td><td>Checkpoint Information and Locks</td>
</table>
</center>

<p>Individual fields of the shm header, except for the
salt values copied from the WAL header, are unsigned integers
in the native byte-order of the host machine.  The salt values
are exact copies from the WAL header and are in whatever byte
order is used by the WAL file.
The size of integers may be 8, 16, 32, or 64 bits.
A detailed breakout of the individual fields of the shm header
follows:

<center>
<i>WAL-Index Header Details</i><br>
<table width="80%" border=1>
................................................................................
<tr>
<td>24..31</td><td>aFrameCksum</td>
<td>Checksum of the last frame in the WAL file.
</tr>
<tr>
<td>32..39</td><td>aSalt</td>
<td>The two salt value copied from the WAL file header.
These values are in the byte-order of the WAL file, which
might be different from the native byte-order of the
machine.
</tr>
<tr>
<td>40..47</td><td>aCksum</td>
<td>A checksum over bytes 0 through 39 of this header.
</tr>
<tr>
<td>48..95</td><td>&nbsp;</td>