Alessandro Benedetti commented on SOLR-10130:

What was causing the Query time slowdown for prefix queries ?
Has this been discovered ?

> Serious performance degradation in Solr 6.4.1 due to the new metrics 
> collection
> -------------------------------------------------------------------------------
>                 Key: SOLR-10130
>                 URL: https://issues.apache.org/jira/browse/SOLR-10130
>             Project: Solr
>          Issue Type: Bug
>      Security Level: Public(Default Security Level. Issues are Public) 
>          Components: metrics
>    Affects Versions: 6.4.1
>         Environment: Centos 7, OpenJDK 1.8.0 update 111
>            Reporter: Ere Maijala
>            Assignee: Andrzej Bialecki 
>            Priority: Blocker
>              Labels: perfomance
>             Fix For: master (7.0), 6.4.2
>         Attachments: SOLR-10130.patch, SOLR-10130.patch, 
> solr-8983-console-f1.log
> We've stumbled on serious performance issues after upgrading to Solr 6.4.1. 
> Looks like the new metrics collection system in MetricsDirectoryFactory is 
> causing a major slowdown. This happens with an index configuration that, as 
> far as I can see, has no metrics specific configuration and uses 
> luceneMatchVersion 5.5.0. In practice a moderate load will completely bog 
> down the server with Solr threads constantly using up all CPU (600% on 6 core 
> machine) capacity with a load that normally  where we normally see an average 
> load of < 50%.
> I took stack traces (I'll attach them) and noticed that the threads are 
> spending time in com.codahale.metrics.Meter.mark. I tested building Solr 
> 6.4.1 with the metrics collection disabled in MetricsDirectoryFactory getByte 
> and getBytes methods and was unable to reproduce the issue.
> As far as I can see there are several issues:
> 1. Collecting metrics on every single byte read is slow.
> 2. Having it enabled by default is not a good idea.
> 3. The comment "enable coarse-grained metrics by default" at 
> https://github.com/apache/lucene-solr/blob/branch_6x/solr/core/src/java/org/apache/solr/update/SolrIndexConfig.java#L104
>  implies that only coarse-grained metrics should be enabled by default, and 
> this contradicts with collecting metrics on every single byte read.

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