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https://issues.apache.org/jira/browse/SOLR-9824?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15728786#comment-15728786
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David Smiley commented on SOLR-9824:
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Fair points Mark.
I think the root fix of the problem I experienced is to modify
ConcurrentUpdateSolrClient so that there is a leading and trailing marker.
Arguably this should be the job of the RequestWriter so that CUSC doesn't have
to make format assumptions. _Hopefully_ no changes to javabin encoding are
needed; but until I next look closer at this, I'm not sure if it's avoidable.
Perhaps JavaBinUpdateRequestCodec may need tweaks too.
To address this more generally for formats other than Javabin, I think the
other formats could be improved to set lastDocInBatch. This should of course
apply even if the document isn't a "batch". Those formats could initially
trigger the poll time to be 250ms (configurable via
{{-Dsolr.cloud.replication.poll-queue-time-ms}} knowing that it likely won't
get hit. For formats that have yet to be updated, I tend to think a non-zero
value should be the default; perhaps 25ms?
> Documents indexed in bulk are replicated using too many HTTP requests
> ---------------------------------------------------------------------
>
> Key: SOLR-9824
> URL: https://issues.apache.org/jira/browse/SOLR-9824
> Project: Solr
> Issue Type: Improvement
> Security Level: Public(Default Security Level. Issues are Public)
> Components: SolrCloud
> Affects Versions: 6.3
> Reporter: David Smiley
>
> This takes awhile to explain; bear with me. While working on bulk indexing
> small documents, I looked at the logs of my SolrCloud nodes. I noticed that
> shards would see an /update log message every ~6ms which is *way* too much.
> These are requests from one shard (that isn't a leader/replica for these docs
> but the recipient from my client) to the target shard leader (no additional
> replicas). One might ask why I'm not sending docs to the right shard in the
> first place; I have a reason but it's besides the point -- there's a real
> Solr perf problem here and this probably applies equally to
> replicationFactor>1 situations too. I could turn off the logs but that would
> hide useful stuff, and it's disconcerting to me that so many short-lived HTTP
> requests are happening, somehow at the bequest of DistributedUpdateProcessor.
> After lots of analysis and debugging and hair pulling, I finally figured it
> out.
> In SOLR-7333 ([~tpot]) introduced an optimization called
> {{UpdateRequest.isLastDocInBatch()}} in which ConcurrentUpdateSolrClient will
> poll with a '0' timeout to the internal queue, so that it can close the
> connection without it hanging around any longer than needed. This part makes
> sense to me. Currently the only spot that has the smarts to set this flag is
> {{JavaBinUpdateRequestCodec.unmarshal.readOuterMostDocIterator()}} at the
> last document. So if a shard received docs in a javabin stream (but not
> other formats) one would expect the _last_ document to have this flag.
> There's even a test. Docs without this flag get the default poll time; for
> javabin it's 25ms. Okay.
> I _suspect_ that if someone used CloudSolrClient or HttpSolrClient to send
> javabin data in a batch, the intended efficiencies of SOLR-7333 would apply.
> I didn't try. In my case, I'm using ConcurrentUpdateSolrClient (and BTW
> DistributedUpdateProcessor uses CUSC too). CUSC uses the RequestWriter
> (defaulting to javabin) to send each document separately without any leading
> marker or trailing marker. For the XML format by comparison, there is a
> leading and trailing marker (<stream> ... </stream>). Since there's no outer
> container for the javabin unmarshalling to detect the last document, it marks
> _every_ document as {{req.lastDocInBatch()}}! Ouch!
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