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From s...@isshomefront.com
Subject RE: Strange "spikes" in query response times...any ideas where else to look?
Date Fri, 29 Jun 2012 01:20:04 GMT
Michael,

Thank you for responding...and for the excellent questions.

1) We have never seen this response time spike with a user-interactive  
search. However, in the span of about 40 minutes, which included about  
82,000 queries, we only saw a handful of near-equally distributed  
"spikes". We have tried sending queries from the admin tool while the  
test was running, but given those odds, I'm not surprised we've never  
"hit" on one of those few spikes we are seeing in the test results.

2) Good point and I should have mentioned this. We are using multiple  
methods to track these response times.
   a) Looking at the catalina.out file and plotting the response times  
recorded there (I think this is logging the QTime as seen by Solr).
   b) Looking at what JMeter is reporting as response times. In  
general, these are very close if not identical to what is being seen  
in the Catalina.out file. I have not run a line-by-line comparison,  
but putting the query response graphs next to each other shows them to  
be nearly (or possibly exactly) the same. Nothing looked out of the  
ordinary.

3) We are using multiple threads. Before your email I was looking at  
the results, doing some math, and double checking the reports from  
JMeter. I did notice that our throughput is much higher than we meant  
for it to be. JMeter is set up to run 15 threads from a single test  
machine...but I noticed that the JMeter report is showing close to 47  
queries per second. We are only targeting TWO to FIVE queries per  
second. This is up next on our list of things to look at and how to  
control more effectively. We do have three separate machines set up  
for JMeter testing and we are investigating to see if perhaps all  
three of these machines are inadvertently being launched during the  
test at one time and overwhelming the server. This *might* be one  
facet of the problem. Agreed on that.

Even as we investigate this last item regarding the number of  
users/threads, I wouldn't mind any other thoughts you or anyone else  
had to offer. We are checking on this user/threads issue and for the  
sake of anyone else you finds this discussion useful I'll note what we  
find.

Thanks again.

Peter S. Lee
ProQuest

Quoting Michael Ryan <mryan@moreover.com>:

> A few questions...
>
> 1) Do you only see these spikes when running JMeter? I.e., do you  
> ever see a spike when you manually run a query?
>
> 2) How are you measuring the response time? In my experience there  
> are three different ways to measure query speed. Usually all of them  
> will be approximately equal, but in some situations they can be  
> quite different, and this difference can be a clue as to where the  
> bottleneck is:
>   1) The response time as seen by the end user (in this case, JMeter)
>   2) The response time as seen by the container (for example, in  
> Jetty you can get this by enabling logLatency in jetty.xml)
>   3) The "QTime" as returned in the Solr response
>
> 3) Are you running multiple queries concurrently, or are you just  
> using a single thread in JMeter?
>
> -Michael
>
> -----Original Message-----
> From: solr@isshomefront.com [mailto:solr@isshomefront.com]
> Sent: Thursday, June 28, 2012 7:56 PM
> To: solr-user@lucene.apache.org
> Subject: Strange "spikes" in query response times...any ideas where  
> else to look?
>
> Greetings all,
>
> We are working on building up a large Solr index for over 300 million
> records...and this is our first look at Solr. We are currently running
> a set of unique search queries against a single server (so no
> replication, no indexing going on at the same time, and no distributed
> search) with a set number of records (in our case, 10 million records
> in the index) for about 30 minutes, with nearly all of our searches
> being unique (I say "nearly" because our set of queries is unique, but
> I have not yet confirmed that JMeter is selecting these queries with
> no replacement).
>
> We are striving for a 2 second response time on the average, and
> indeed we are pretty darned close. In fact, if you look at the average
> responses time, we are well under the 2 seconds per query.
> Unfortunately, we are seeing that about once every 6 minutes or so
> (and it is not a regular event...exactly six minutes apart...it is
> "about" six minutes but it fluctuates) we get a single query that
> returns in something like 15 to 20 seconds
>
> We have been trying to identify what is causing this "spike" every so
> often and we are completely baffled. What we have done thus far:
>
> 1) Looked through the SAR logs and have not seen anything that
> correlates to this issue
> 2) Tracked the JVM statistics...especially the garbage
> collections...no correlations there either
> 3) Examined the queries...no pattern obvious there
> 4) Played with the JVM memory settings (heap settings, cache settings,
> and any other settings we could find)
> 5) Changed hardware: Brand new 4 processor, 8 gig RAM server with a
> fresh install of Redhat 5.7 enterprise, tried on a large instance of
> AWS EC2, tried on a fresh instance of a VMWare based virtual machine
> from our own data center) an still nothing is giving us a clue as to
> what is causing these "spikes"
> 5) No correlation found between the number of hits returned and the spikes
>
>
> Our data is very simple and so are the queries. The schema consists of
> 40 fields, most of which are "string" fields, 2 of which are
> "location" fields, and a small handful of which are integer fields.
> All fields are indexed and all fields are stored.
>
> Our queries are also rather simple. Many of the queries are a simple
> one-field search. The most complex query we have is a 3-field search.
> Again, no correlation has been established between the query and these
> spikes. Also, about 60% of our queries return zero hits (on the
> assumption that we want to make solr search its entire index every so
> often. 60% is more than we intended and we will fix that soon...but
> that is what is currently happening. Again, no correlation found
> between spikes and 0-hit returned queries).
>
> For some time we were testing with 100 million records in the index
> and the aggregate data looked quite good. Most queries were returning
> in under 2 seconds. Unfortunately, it was when we looked at the
> individual data points that we found spikes every 6-8 minutes or so
> hitting sometimes as high as 150 seconds!
>
> We have been testing with 100 million records in the index, 50 million
> records in the index, 25 million, 20 million, 15 million, and 10
> million records. As I  indicated at the start, we are now at 10
> million records with 15-20 seconds spikes.
>
> As we have decreased the number of records in the index,the size (but
> not the frequency) of the spikes has been dropping.
>
> My question is: Is this type of behavior normal for Solr when it is
> being overstressed? I've read of lots of people with far more
> complicated schemas running MORE than 10 million records in an index
> and never once complained about these spikes. Since I am new at this,
> I am not sure what Solr's "failure mode" looks like when it has too
> many records to search.
>
> I am hoping someone looking at this note can at least give me another
> direction to look. 10 million records searched in less than 2 seconds
> most of the time is great...but those 10 and 20 seconds spikes are not
> going to go over well with our customers...and I somehow think there
> is more we should be able to do here.
>
> Thanks.
>
> Peter S. Lee
> ProQuest
>
>




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