<div dir="ltr"><br><div class="gmail_extra"><br><br><div class="gmail_quote">On Fri, Mar 21, 2014 at 4:04 AM, Sean Dague <span dir="ltr"><<a href="mailto:sean@dague.net" target="_blank">sean@dague.net</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div class="">On 03/20/2014 06:18 PM, Joe Gordon wrote:<br>
><br>
><br>
><br>
> On Thu, Mar 20, 2014 at 3:03 PM, Alexei Kornienko<br>
</div><div class="">> <<a href="mailto:alexei.kornienko@gmail.com">alexei.kornienko@gmail.com</a> <mailto:<a href="mailto:alexei.kornienko@gmail.com">alexei.kornienko@gmail.com</a>>> wrote:<br>
><br>
> Hello,<br>
><br>
> We've done some profiling and results are quite interesting:<br>
> during 1,5 hour ceilometer inserted 59755 events (59755 calls to<br>
> record_metering_data)<br>
> this calls resulted in total 2591573 SQL queries.<br>
><br>
> And the most interesting part is that 291569 queries were ROLLBACK<br>
> queries.<br>
> We do around 5 rollbacks to record a single event!<br>
><br>
> I guess it means that MySQL backend is currently totally unusable in<br>
> production environment.<br>
><br>
><br>
> It should be noticed that SQLAlchemy is horrible for performance, in<br>
> nova we usually see sqlalchemy overheads of well over 10x (time<br>
> nova.db.api call vs the time MySQL measures when slow log is recording<br>
> everything).<br>
<br>
</div>That's not really a fair assessment. Python object inflation takes time.<br>
I do get that there is SQLA overhead here, but even if you trimmed it<br>
out you would not get the the mysql query time.<br>
<br></blockquote><div><br></div><div>To give an example from nova:</div><div><br></div><div>doing a nova list with no servers:</div><div><br></div><div><div>stack@devstack:~/devstack$ nova --timing list </div><div><br></div>
<div><div>| GET <a href="http://10.0.0.16:8774/v2/a82ededa9a934b93a7184d06f302d745/servers/detail">http://10.0.0.16:8774/v2/a82ededa9a934b93a7184d06f302d745/servers/detail</a> | 0.0817470550537 |</div></div></div><div><br>
</div><div>So nova command takes 0.0817470550537 seconds.</div><div><br></div><div>Inside the nova logs (when putting a timer around all nova.db.api calls [1] ), nova.db.api.instance_get_all_by_filters takes 0.06 seconds:</div>
<div><br></div><div><div> 2014-03-21 20:58:46.760 DEBUG nova.db.api [req-91879f86-7665-4943-8953-41c92c42c030 demo demo] 'instance_get_all_by_filters' 0.06 seconds timed /mnt/stack/nova/nova/db/api.py:1940</div>
</div><div><br></div><div>But the sql slow long reports the same query takes only 0.001006 seconds with a lock_time of 0.000269 for a total of 0.00127 seconds.</div><div><br></div><div><div> # Query_time: 0.001006 Lock_time: 0.000269 Rows_sent: 0 Rows_examined: 0</div>
<div><br></div></div><div><br></div><div>So in this case only 2% of the time that nova.db.api.instance_get_all_by_filters takes is spent inside of mysql. Or to put it differently nova.db.api.instance_get_all_by_filters is 47 times slower then the raw DB call underneath.</div>
<div><br></div><div>Yes I agree that that turning raw sql data into python objects should take time, but I just don't think it should take 98% of the time.</div><div><br></div><div>[1] <a href="https://github.com/jogo/nova/commit/7743ee366bbf8746f1c0f634f29ebf73bff16ea1">https://github.com/jogo/nova/commit/7743ee366bbf8746f1c0f634f29ebf73bff16ea1</a></div>
<div><br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
That being said, having Ceilometer's write path be highly tuned and not<br>
use SQLA (and written for every back end natively) is probably appropriate.<br></blockquote><div><br></div><div>While I like this idea, they loose free postgresql support by dropping SQLA. But that is a solvable problem.</div>
<div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
<div class=""><div class="h5"><br>
-Sean<br>
<br>
--<br>
Sean Dague<br>
Samsung Research America<br>
<a href="mailto:sean@dague.net">sean@dague.net</a> / <a href="mailto:sean.dague@samsung.com">sean.dague@samsung.com</a><br>
<a href="http://dague.net" target="_blank">http://dague.net</a><br>
<br>
</div></div><br>_______________________________________________<br>
OpenStack-dev mailing list<br>
<a href="mailto:OpenStack-dev@lists.openstack.org">OpenStack-dev@lists.openstack.org</a><br>
<a href="http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev" target="_blank">http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev</a><br>
<br></blockquote></div><br></div></div>