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https://issues.apache.org/jira/browse/SOLR-17656?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Chris M. Hostetter updated SOLR-17656:
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Attachment: SOLR-17656.patch
Status: Open (was: Open)
The attached patch implements this idea via a new {{skipLeaderRecovery}}
replica property.
This patch leverages existing {{skipRecovery}} logic in {{ZkController}} – all
it does is add a new condition in which {{skipRecovery}} may be set to
{{{}true{}}}.
The new logic includes sanity checks to ensure that event if
{{{}skipLeaderRecovery==true{}}}, the property will be ignored (and an error
logged) if either:
* the replica type {{requireTransactionLog}}
* the replica does not have *ANY* local index commit (ie: was restarted before
it ever did a single fetch from the leader)
{{TestPullReplica}} has been updated to confirm that this new property can
allow a PULL replica on a restarted solr node to become ACTIVE even if the
leader is DOWN.
Feedback welcome. I feel like it would be pretty useful, and that the patch is
basically good to go from a code standpoint – but it obviously needs some
ref-guide updates.
(i was holding off pending any objections to the name and/or restrictions on
when it's respected. I'm assuming it would make sense to document this
[HERE|https://solr.apache.org/guide/solr/latest/deployment-guide/solrcloud-shards-indexing.html#recovery-with-pull-replicas])
> Add expert level option to allowe PULL replicas to go ACTIVE w/o RECOVERING
> ---------------------------------------------------------------------------
>
> Key: SOLR-17656
> URL: https://issues.apache.org/jira/browse/SOLR-17656
> Project: Solr
> Issue Type: New Feature
> Reporter: Chris M. Hostetter
> Assignee: Chris M. Hostetter
> Priority: Major
> Attachments: SOLR-17656.patch
>
>
> In situations where a Solr cluster undergoes a rolling restart (or some other
> "catastrophic" failure situations requiring/causing solr node restarts) there
> can be a snowball effect of poor performance (or even solr node crashing) due
> to fewer then normal replicas serving query requests while replicas on
> restarting nodes are DOWN or RECOVERING – especially if shard leaders are
> also affected, and (restarting) replicas first must wait for a leader
> election before they can recover (or wait to finish recovery from an
> over-worked leader).
> For NRT type usecases, RECOVERING is really a necessary evil to ensure every
> replicas is up to date before handling NRT requests – but in the case of PULL
> replicas, which are expected to routinely "lag" behind their leader, I've
> talked to a lot of Solr users w/usecases where they would be happy to have
> PULL replicas back online serving "stale" data ASAP, and let normal
> IndexFetching "catchup" with the leader later.
> I propose we support a new "advanced" replica property that can be set on
> PULL replicas by expert level users, to indicate: on (re)init, these replicas
> may skip RECOVERING and go directly to ACTIVE.
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