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From Erick Erickson <erickerick...@gmail.com>
Subject Re: Inconsistency in results between replicas using CloudSolrClient
Date Tue, 01 Aug 2017 21:38:25 GMT
You're understanding is correct.

As for how people cope? Mostly they ignore it. The actual number of
times people notice this is usually quite small, mostly it surfaces
when automated test suites are run.

If you must lock this up, and you can stand the latency you could add
a timestamp for each document and auto-add an FQ clause like:
fq=timestamp:[* TO NOW-soft_commit_interval_plus_some_windage]

Note, though, that this not an fq clause that can be re-used, see:
https://lucidworks.com/2012/02/23/date-math-now-and-filter-queries/ so
either it'd be something like:
fq=timestamp:[* TO NOW/MINUTE-soft_commit_interval_plus_some_windage]
or
fq=timestamp:{!cache=false}[* TO NOW-soft_commit_interval_plus_some_windage]

and would inevitably make the latency between when something was
indexed and available for search longer.

You can also reduce your soft commit interval to something short, but
that has other problems.

see: SOLR-6606, but it looks like other priorities have gotten in the
way of it being committed.

Best,
Erick

On Tue, Aug 1, 2017 at 1:50 PM, Chris Troullis <cptroullis@gmail.com> wrote:
> Hi,
>
> I think I know the answer to this question, but just wanted to verify/see
> what other people do to address this concern.
>
> I have a Solr Cloud setup (6.6.0) with 2 nodes, 1 collection with 1 shard
> and 2 replicas (1 replica per node). The nature of my use case requires
> frequent updates to Solr, and documents are being added constantly
> throughout the day. I am using CloudSolrClient via SolrJ to query my
> collection and load balance across my 2 replicas.
>
> Here's my question:
>
> As I understand it, because of the nature of Solr Cloud (eventual
> consistency), and the fact that the soft commit timings on the 2 replicas
> will not necessarily be in sync, would it not be possible to run into a
> scenario where, say a document gets indexed on replica 1 right before a
> soft commit, but indexed on replica 2 right after a soft commit? In this
> scenario, using the load balanced CloudSolrClient, wouldn't it be possible
> for a user to do a search, see the newly added document because they got
> sent to replica 1, and then search again, and the newly added document
> would disappear from their results since they got sent to replica 2 and the
> soft commit hasn't happened yet?
>
> If so, how do people typically handle this scenario in NRT search cases? It
> seems like a poor user experience if things keep disappearing and
> reappearing from their search results randomly. Currently the only thought
> I have to prevent this is to write (or extend) my own solr client to stick
> a user's session to a specific replica (unless it goes down), but still
> load balance users between the replicas. But of course then I have to
> manage all of the things CloudSolrClient manages manually re: cluster
> state, etc.
>
> Can anyone confirm/deny my understanding of how this works/offer any
> suggestions to eliminate the scenario in question from occurring?
>
> Thanks,
>
> Chris

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