FW: Safe to change numVersionBuckets?

-----Original Message-----
From: Shawn Heisey [mailto:elyograg@elyograg.org]
Sent: 31 March 2018 11:00
To: solr-user@lucene.apache.org
Subject: Re: Safe to change numVersionBuckets?

On 3/30/2018 10:24 PM, Randy Fradin wrote:
> I understand from reading the discussion in SOLR-6820 that 65536 is
> the recommended default for this setting now because it results in
> higher document write rates than the old default of 256. I would like
> to reduce my heap utilization and I'm OK with somewhat slower document
> writing throughput. My question is, it is safe to reduce the value of
> numVersionBuckets on all of my existing cores without reindexing my data?
>
> My solrconfig.xml contains this for all of my collections:
>
> <updateHandler class="solr.DirectUpdateHandler2">
> <updateLog>
> <str name="dir">${solr.ulog.dir:}</str>
> <int
name="numVersionBuckets">${solr.ulog.numVersionBuckets:65536}</int>
> </updateLog>
> </updateHandler>

It looks like that is something that applies during indexing, and doesn't
affect the data that's already indexed.

If you do heavy indexing, then you probably shouldn't reduce it quite that
far.  If your indexing is light, then a low value is not likely to be
problematic.

> Assuming it is safe to change, can I just add a vm arg to the Solr
> process like "-Dsolr.ulog.numVersionBuckets=256" to override the value
> for all cores at once? Or do I have to change and re-upload the
> solrconfig.xml files and reload the cores?

Setting it with the system property will require restarting every Solr
service.  If you change it in solrconfig.xml and then upload the updated
config to zookeeper under the same config name, all you will need to do to
apply the change is reload collections using that config.

With 3300 cores per server, a reload is probably significantly less stress
on the system than a full Solr restart.

Thanks,
Shawn