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https://issues.apache.org/jira/browse/OAK-2106?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14989192#comment-14989192
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Tomek Rękawek edited comment on OAK-2106 at 12/8/15 10:51 AM:
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After discussing with Marcel I tried a different approach, in which the Oak
instance connects directly to all secondary instances and reads their _lastRev
for the root. Then it's able to check if the secondary instance contains an
up-to-date parent and - therefore - if the request document can be read from
the nearest Mongo instance.
was (Author: tomek.rekawek):
After discussing with Marcel I tried a different approach, in which the Oak
instance connects directly to all secondary instances and reads their _lastRev
for the root. Then it's able to check if the secondary instance contains an
up-to-date parent and - therefore - if the request document can be read from
the nearest Mongo instance.
Pull request:
https://github.com/apache/jackrabbit-oak/pull/41
Patch file:
https://github.com/apache/jackrabbit-oak/pull/41.diff
> Optimize reads from secondaries
> -------------------------------
>
> Key: OAK-2106
> URL: https://issues.apache.org/jira/browse/OAK-2106
> Project: Jackrabbit Oak
> Issue Type: Improvement
> Components: core, mongomk
> Reporter: Marcel Reutegger
> Assignee: Marcel Reutegger
> Labels: performance, scalability
>
> OAK-1645 introduced support for reads from secondaries under certain
> conditions. The current implementation checks the _lastRev on a potentially
> cached parent document and reads from a secondary if it has not been
> modified in the last 6 hours. This timespan is somewhat arbitrary but
> reflects the assumption that the replication lag of a secondary shouldn't
> be more than 6 hours.
> This logic should be optimized to take the actual replication lag into
> account. MongoDB provides information about the replication lag with
> the command rs.status().
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