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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Can’t you do the select and update as part of one
transaction? <o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>For example with MySQL:<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:windowtext'>START TRANSACTION;<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:windowtext'>SELECT @A:=SUM(salary) FROM table1 WHERE type=1;<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:windowtext'>UPDATE table2 SET summary=@A WHERE type=1;<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:windowtext'>COMMIT;<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>The transaction may need to be changed to serializable as well.
I don’t know how the DHCP RFC handles preallocations.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>You could probably use Repeatable Read level if it is acceptable
to mark an address as taken when a DHCPOFFER is sent while waiting for a
DHCPREQUEST from the client, so long as the address if confirmed to be free
before the DHCPACK is sent, or a DHCPNAK in the case that the address was
offered to multiple clients. <o:p></o:p></span></p>
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<p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span
style='font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D'>Ben
Wiechman<br>
<br>
</span><span style='color:#1F497D'><o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
</div>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
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<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif";
color:windowtext'>From:</span></b><span style='font-size:10.0pt;font-family:
"Tahoma","sans-serif";color:windowtext'>
freeradius-users-bounces+ben=wisper-wireless.com@lists.freeradius.org
[mailto:freeradius-users-bounces+ben=wisper-wireless.com@lists.freeradius.org] <b>On
Behalf Of </b>Padam J Singh<br>
<b>Sent:</b> Thursday, January 15, 2009 9:39 AM<br>
<b>To:</b> FreeRadius users mailing list<br>
<b>Subject:</b> Re: Handing out duplicate IP addresses<o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Helvetica","sans-serif"'>Hello
Ivan,<br>
<br>
Would adding a mutex around the select-update code in the sqlippool module
solve this issue? <br>
<br>
Padam<br>
</span><br>
<a href="mailto:tnt@kalik.net">tnt@kalik.net</a> wrote: <o:p></o:p></p>
<blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><pre>The requests all came in at the same time, to the second (among others),<o:p></o:p></pre><pre>its like FR took 3 requests and looked at the database at the exact same<o:p></o:p></pre><pre>time, saw it was an available IP and all those 3 requests assigned it.<o:p></o:p></pre><pre> <o:p></o:p></pre></blockquote>
<pre><o:p> </o:p></pre><pre>That can't be avoided. SELECT (allocate-find) will always work much<o:p></o:p></pre><pre>faster than UPDATE (allocate-update).<o:p></o:p></pre><pre><o:p> </o:p></pre><pre> <o:p></o:p></pre>
<blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><pre>My NAS rejects two of the 3 because the IP is assigned,<o:p></o:p></pre><pre> <o:p></o:p></pre></blockquote>
<pre><o:p> </o:p></pre><pre>I think that you make a good point here. If the allocate-update query was<o:p></o:p></pre><pre>made to fail in the case that the IP address was already issued to<o:p></o:p></pre><pre>another thread between allocate-find and allocate-update (by expanding<o:p></o:p></pre><pre>it with AND expiry_time IS NULL in WHERE), point of failure will be in<o:p></o:p></pre><pre>sqlippool module and not on the NAS. Logic can then perhaps try to issue<o:p></o:p></pre><pre>a new IP address (best just once more in order not to create a loop).<o:p></o:p></pre><pre>That way issuing same IP address to multiple threads can be handled by<o:p></o:p></pre><pre>the sqlippool module.<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>Ivan Kalik<o:p></o:p></pre><pre>Kalik Informatika ISP<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>-<o:p></o:p></pre><pre>List info/subscribe/unsubscribe? See <a
href="http://www.freeradius.org/list/users.html">http://www.freeradius.org/list/users.html</a><o:p></o:p></pre><pre><o:p> </o:p></pre><pre> <o:p></o:p></pre>
<p class=MsoNormal><br>
<br>
<o:p></o:p></p>
<pre>-- <o:p></o:p></pre><pre>PGP Id 9EED2E09<o:p></o:p></pre></div>
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