[Mongrel] Server timeouts

Pete DeLaurentis pete at nextengine.com
Fri Nov 2 21:53:10 EDT 2007

Thanks for the DB profiling tips Dave.  From some basic top  
monitoring, I've seen that my server is topping out at 100% CPU.   
I'll check out mysqlreport and learn more about why it's using this  
kind of power.


On Nov 2, 2007, at 6:11 PM, Dave Cheney wrote:

> Hi Pete,
> 	If you suspect queries are your pain point then I would do the
> following to get a sense of what you app is doing under the hood.
> 	Get a copy of http://hackmysql.com/mysqlreport and use it against
> your db. It can assist in tweaking innodb or myisam table configs.
> 	Turn on slow query logging, add the lines
> 	log_slow_queries=/usr/local/mysql/data/mysql-slow.log (adjust path as
> necessary)
> 	log-queries-not-using-indexes
> 	To your /etc/my.cnf and restart the db. This will log any query that
> takes longer than 1 second to run (will only spot the really heinous
> ones, in a busy web app a 1 second query is game over). This also logs
> queries which do not use and index, hence scale badly as your tables
> grow.
> 	Recent versions of linux have an excellent vmstat and iostat, have
> them running in a wind during busy times of the day and see how your
> db machine handles it. Is it really out of CPU, or does your dataset
> not fit in memory and you pulling huge blobs of data off the disk
> because of poorly specified queries, or worse spending it rashly by
> creating many temporary tables.
> 	I have found that time spent optimising db queries, and rethinking
> the datamodel to be more sql efficient pays off in the long run vs
> throwing hardware at the problem.
> Cheers
> Dave
> On 03/11/2007, at 5:38 AM, Pete DeLaurentis wrote:
>> Yeah, all the foreign keys are indexed.  I'm also caching what I can
>> in our ruby app's memory.
>> It seems to be the database writes that are taking up a lot of the
>> time.  The other offender are some multiple JOINs we're doing.
>> I've ordered more processors for the database server, and am clearing
>> off a second machine so I can get a little MySQL cluster going.  Any
>> advice on this is welcome since I've never scaled a database server
>> before.
>> As the database gets faster, it will help reduce the timeouts.  But
>> demand + server load has a way of sneaking up on you.  I'm looking
>> for a way of making sure our server is less likely to timeout on
>> users when we run into system bottlenecks (now + in the future).
>> Thanks,
>> Pete
>> On Nov 2, 2007, at 11:29 AM, barsalou wrote:
>>> Pete,
>>> What about the DB is the bottleneck?  I'm assuming you have already
>>> looked at indexing and the like.
>>> Mike B.
>>> Quoting Pete DeLaurentis <pete at nextengine.com>:
>>>> Hi guys,
>>>> Does anyone know if mongrel has a built-in timeout for requests  
>>>> that
>>>> take too long?  If so, how do you increase it?
>>>> I've found that some server requests are timing out.  Complicated
>>>> requests are already being farmed out to asynchronous processes.
>>>> But
>>>> some of the more basic requests are timing out when we have our  
>>>> peak
>>>> server load in the mornings (the bottleneck is the database  
>>>> server).
>>>> There are a couple possible locations for the timeout I'm seeing:
>>>> 1. Mongrel
>>>> 2. Lighttpd
>>>> 3. Client browser / application
>>>> On my local development server, it does not timeout, leading me to
>>>> believe it's not #3.
>>>> Any feedback is appreciated.
>>>> Thanks,
>>>> Pete
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