Hi Shawn,

I agree on Disk I/O versus available memory about Solr performances.
However for heavy indexing and heavy searching context, even with a lot of
RAM, disk I/O should be critical.

My concern is also about write I/O for Zookeeper transactions log. My
understanding is that is critical not as much for Solrcloud performances
but mainly for SolrCloud stability.

Sometimes even with best practices respect and all possible configuration
tuning, Solrcoud is not stable or not performant due to lake of hardware
resources. Monitoring CPU, CPU load, iowait, jvm GC, … should highlight
theses lake of ressources. If the hardware is undersized, we need metrics
in order to explain and demonstrate this to the customer (furthermore if
the infrastructure provider do not want admit there are issues with
hardware or virtualization). That was the meaning of my question about
“decent disk I/O”.



Le ven. 9 mars 2018 à 00:40, Shawn Heisey <apa...@elyograg.org> a écrit :

> On 3/8/2018 2:55 PM, Dominique Bejean wrote:
> > Disk I/O are critical for high performance Solrcloud.
> This statement has truth to it, but if your system is correctly sized,
> disk performance will not have much of an impact on Solr performance.
> If upgrading to faster disks does improves long-term query performance,
> the system probably doesn't have enough memory installed.  There can be
> other causes, but that is the most common.
> When there is enough memory available to allow the operating system to
> effectively cache the index data, Solr will not need to access the disk
> much at all for queries -- all that data will be already in memory.
> Indexing will still be dependent on disk performance even when there is
> plenty of memory, because that will require writing new data to the disk.
> https://wiki.apache.org/solr/SolrPerformanceProblems
> This is my hammer.  To me, your question looks like a nail.  :)
> Thanks,
> Shawn
> --
Dominique Béjean
06 08 46 12 43

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