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From Miguel González Castaños <miguel_3_gonza...@yahoo.es>
Subject Re: Tomcat pausing and no java process
Date Thu, 03 May 2012 17:02:59 GMT
On 03/05/2012 18:21, Christopher Schultz wrote:
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> Miguel,
>
> On 5/3/12 11:37 AM, Miguel González Castaños wrote:
>> We had several crashes today:
>>
>> First - 1 outofmemory error Second- 3 Tomcat pausing
> Do you mean that Tomcat actually paused its connectors, or do you mean
> that your site became unresponsive? Were you able to capture a thread
> dump during this unresponsive period? Did the JVM recover or did you
> have to kill it and restart. If you had to kill it, that's called
> beign "locked-up" and not just pausing for a while.
Site became unresponsive. When I saw in catalina.out that the connector 
was pausing and the website was not responsive, I checked the java 
process and was dead, so I couldn't get a thread dump

>
> If you can't take a thread dump during these "pauses", you'll never
> know what is happening.
Any setting that can generate a dump automatically as for out of memory 
errors?
>
> Are you using a database? Are you using pooled connections? If so,
> enable "abandoned" tracing if that's a possibility for you (Tomcat's
> two built-in choices of dbcp can do abandoned tracing).

Yes, a mysql database and pooled connections. How can I enable that 
abandoned tracing?

I enabled slow queries for mysql, but the developer claims the queries 
are fine (although some report more than a second to be run).


>
>> Third - 2 or 3 times where catalina.out didn't show any error and
>> tomcat died, only a big increase of memory use right before the
>> java process died. That's why I assumed that maybe I have set the
>> heap memory too high (I set it up because of the out of memory
>> errors). That's why I googled to see if anyone had seen issues and
>> that's why I reached that URL
>>
>> I have set up this:
>>
>> -XX:+HeapDumpOnOutOfMemoryError -XX:+UseConcMarkSweepGC -Xms128m
>> -Xmx768m -verbose:gc -XX:+PrintGCTimeStamps -XX:+PrintGCDetails
> Great, so you've changed heap size *and* GC strategy and you still
> have no idea what the problem is.
Well, before the heap size was 512m so I have increased it just a little 
(to overcome the outofmemory errors). Is that increase that much?

I can revert the GC strategy. the verbose options for GC are fine?



>
> We had a performance problem last week that was very severe. One of my
> friends said "well, if you're not using concurrent mark-and-sweep,
> then that's probably the problem".  (I'm not sure of the nuances, but
> the default GC on my system is "ConcurrentMarkSweep", so I don't know
> if UseConcMarkSweepGC actually gets you anything). I was skeptical. I
> did my research.
>
> The problem was a missing index on a database table. A simple ALTER
> statement changed 20-second response times back to more reasonable
> sub-100ms response times. No mucking-around with the JVM required.

I'll retake that path of checking mysql indexes and slow queries.

>
> That's hy I suggest that you do some research *in your own
> environment* instead of just guessing at random things and changing
> every setting that you've found via Google.
>
>> I hope this way I can trace if there is any memory leak in the
>> webapp.
> If you have a memory leak in your webapp and you have javamelody, I
> would argue that you should set your heap to the /largest/ you can
> possibly get away with and then watch it over time. A memory leak is
> easy to see over time with a big heap. You are limited by a 32-bit JVM
> and only ~1.5GiB heap limit, so it might be hard. Maybe you've just
> outgrown your hardware.
That we have outgrown our hardware, that's probably for sure. This a 
virtual private server. I have said the owners to move to a dedicated 
server but I guess they want me to squeeze this VPS as much as I can.

Miguel

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