[jira] [Commented] (SOLR-14581) Document the way auto commits work in SolrCloud

["Lucene/Solr QA (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SOLR-14581?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17139416#comment-17139416 ] 

Lucene/Solr QA commented on SOLR-14581:
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|| Vote || Subsystem || Runtime || Comment ||
|| || || || {color:brown} Prechecks {color} ||
|| || || || {color:brown} master Compile Tests {color} ||
|| || || || {color:brown} Patch Compile Tests {color} ||
| {color:green}+1{color} | {color:green} Release audit (RAT) {color} | {color:green}  0m  4s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} Validate source patterns {color} | {color:green}  0m  4s{color} | {color:green} the patch passed {color} |
| {color:green}+1{color} | {color:green} Validate ref guide {color} | {color:green}  0m  4s{color} | {color:green} the patch passed {color} |
|| || || || {color:brown} Other Tests {color} ||
| {color:black}{color} | {color:black} {color} | {color:black}  2m 21s{color} | {color:black} {color} |
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|| Subsystem || Report/Notes ||
| JIRA Issue | SOLR-14581 |
| JIRA Patch URL | https://issues.apache.org/jira/secure/attachment/13005940/SOLR-14581.patch |
| Optional Tests |  ratsources  validatesourcepatterns  validaterefguide  |
| uname | Linux lucene2-us-west.apache.org 4.4.0-170-generic #199-Ubuntu SMP Thu Nov 14 01:45:04 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux |
| Build tool | ant |
| Personality | /home/jenkins/jenkins-slave/workspace/PreCommit-SOLR-Build/sourcedir/dev-tools/test-patch/lucene-solr-yetus-personality.sh |
| git revision | master / 0ea0358 |
| ant | version: Apache Ant(TM) version 1.9.6 compiled on July 20 2018 |
| modules | C: solr/solr-ref-guide U: solr/solr-ref-guide |
| Console output | https://builds.apache.org/job/PreCommit-SOLR-Build/766/console |
| Powered by | Apache Yetus 0.7.0   http://yetus.apache.org |


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> Document the way auto commits work in SolrCloud
> -----------------------------------------------
>
>                 Key: SOLR-14581
>                 URL: https://issues.apache.org/jira/browse/SOLR-14581
>             Project: Solr
>          Issue Type: Bug
>      Security Level: Public(Default Security Level. Issues are Public) 
>          Components: documentation, SolrCloud
>    Affects Versions: master (9.0)
>            Reporter: Bram Van Dam
>            Priority: Minor
>         Attachments: SOLR-14581.patch
>
>
> The documentation is unclear about how auto commits actually work in SolrCloud. A mailing list reply by Erick Erickson proved to be enlightening. 
> Erick's reply verbatim:
> {quote}Each node has its own timer that starts when it receives an update.
> So in your situation, 60 seconds after any give replica gets it’s first
> update, all documents that have been received in the interval will
> be committed.
> But note several things:
> 1> commits will tend to cluster for a given shard. By that I mean
>     they’ll tend to happen within a few milliseconds of each other
>    ‘cause it doesn’t take that long for an update to get from the
>    leader to all the followers.
> 2> this is per replica. So if you host replicas from multiple collections
>    on some node, their commits have no relation to each other. And
>    say for some reason you transmit exactly one document that lands
>    on shard1. Further, say nodeA contains replicas for shard1 and shard2.
>    Only the replica for shard1 would commit.
> 3> Solr promises eventual consistency. In this case, due to all the
>    timing variables it is not guaranteed that every replica of a single
>    shard has the same document available for search at any given time.
>    Say doc1 hits the leader at time T and a follower at time T+10ms.
>    Say doc2 hits the leader and gets indexed 5ms before the 
>    commit is triggered, but for some reason it takes 15ms for it to get
>    to the follower. The leader will be able to search doc2, but the
>   follower won’t until 60 seconds later.{quote}
> Perhaps the subject deserves a section of its own, but I'll attach a patch which includes the gist of Erick's reply as a Tip in the "indexing in SolrCloud"-section.



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