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https://issues.apache.org/jira/browse/OAK-2106?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14160152#comment-14160152
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Marcel Reutegger commented on OAK-2106:
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It would also be good to better align reads from the other cluster nodes with
what is available on a nearby secondary. Right now, we background read the root
document from the primary to find out what other cluster nodes had written.
This way, further reads may need to be directed to the primary as well because
those changes have not yet been replicated to the secondaries. It might be
better to only make those external changes visible when they appear on a nearer
secondary. Subsequent reads could then be performed on that secondary as well.
> 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
>
> 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 24 hours. This timespan is somewhat arbitrary but
> reflects the assumption that the replication lag of a secondary shouldn't
> be more than 24 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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