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From Walter Underwood <>
Subject Re: Solr Cloud has lower performance with more servers
Date Thu, 09 Oct 2014 14:40:52 GMT
Is this a production log of queries, with lots of repeats? If so, you may be seeing the normal
effect of lower cache hit rates.

Check the hit rate for the query result cache in the two setups. With a single machine, the
second occurrence of a query will be a cache hit. With two machines, it will not be if the
two queries are routed to different machines.

I was running some benchmarks here. With one machine, the query cache had a 50% hit rate.
With eight machines, it was 20%.

You can address this with a reverse proxy HTTP cache in front of the cluster, something like

Walter Underwood

On Oct 9, 2014, at 7:21 AM, Yannick <> wrote:

> Hi Toke,
> thanks for your suggestion - definitely an interesting idea. But unfortunately no, no
indexing job is running; those are static indexes being queried. The execution time is also
very consistent in each condition, I did quite a few tests.
> Yann 
> On Thursday, October 9, 2014 3:56 PM, Toke Eskildsen <> wrote:
> On Thu, 2014-10-09 at 15:06 +0200, Yannick wrote:
>> I created a group of 2 Solr servers with a load-balancer in front
>> (Haproxy). I have a batch client that sends requests (read-only)
>> continuously to the load-balancer. The problem is: the performance is
>> slower with 2 servers than it is with a single server (still via the
>> load-balancer, with the second server down, so it's not the
>> load-balancer itself causing the slowdown).
> (speculating a lot here:)
> Is another job updating the indexes while you are batch-searching?
> If so, the slowdown could be explained by the servers disk caches being
> flushed by the indexing job. When a request arrives some cache is
> reclaimed, but is will be a battle between the update and the search
> jobs. With more machines, there will be fewer request/machine, so the
> search-cache has a lower chance of being used again before it is
> reclaimed by the updater.
> Still, worse performance for 2 machines sounds pretty bad.
> - Toke Eskildsen, State and University Library, Denmark

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