[jira] [Updated] (SOLR-8973) TX-frenzy on Zookeeper when collection is put to use

["Janmejay Singh (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SOLR-8973?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Janmejay Singh updated SOLR-8973:
---------------------------------
    Attachment: SOLR-8973.patch

Patch allows a node to wait upto 1 minute for collection to become visible. The wait-time can perhaps be made configurable, but this is sufficient (because tick time on zk is usually 2 seconds and delay is never more than 2 ticks).

> TX-frenzy on Zookeeper when collection is put to use
> ----------------------------------------------------
>
>                 Key: SOLR-8973
>                 URL: https://issues.apache.org/jira/browse/SOLR-8973
>             Project: Solr
>          Issue Type: Bug
>          Components: SolrCloud
>    Affects Versions: 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, master, 5.6
>            Reporter: Janmejay Singh
>              Labels: collections, patch-available, solrcloud, zookeeper
>         Attachments: SOLR-8973.patch
>
>
> This is to do with a distributed data-race. Core-creation happens at a time when collection is not yet visible to the node. In this case a fallback code-path is used which de-references collection-state lazily (on demand) as opposed to setting a watch and keeping it cached locally.
> Due to this, as requests towards the core mount, it generates ZK fetch for collection proportionately. On a large solr-cloud cluster, this generates several Gbps of TX traffic on ZK nodes. This affects indexing throughput(which floors) in addition to running ZK node out of network bandwidth. 
> On smaller solr-cloud clusters its hard to run into, because probability of this race materializing reduces.



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