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https://issues.apache.org/jira/browse/OAK-1750?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13976638#comment-13976638
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Michael Marth commented on OAK-1750:
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[~chetanm], if you change the write concern to "replica ack" in situations
where the replica members already lag behind: would that block the first write
that is made with the new write concern until the replication queue is worked
through?
Anyway, I am not sure if we want to slow down writes in such situations. But if
we do, we could consider the Commit Hook that [~mduerig] provided to limit
commit rates (OAK-1659).
> Adapt write concern dynamically to manage replication lag
> ---------------------------------------------------------
>
> Key: OAK-1750
> URL: https://issues.apache.org/jira/browse/OAK-1750
> Project: Jackrabbit Oak
> Issue Type: Wish
> Components: mongomk
> Reporter: Chetan Mehrotra
> Assignee: Chetan Mehrotra
>
> Mongo provides write concern with varying level of durability and performance
> characteristics [1]. When using replica sets its possible that replica member
> lag behind in synching up the changes from primary. This introduces
> replication lag which can increase if the write rate is quite high.
> One of the recommended ways [2], [3] to mitigate such scenarios is to change
> the write concern to higher values (journal ack, replica ack) to as to slow
> down writes on primary
> In MongoDocumentStore it can be supported in following way
> # Have a periodic job which obtains current replSetGetStatus [4]
> # Determine the potential lag from the command result
> # if the lag is significant then change the write concern used in
> MongoDocumentStore to Syned, Journal Ack, Replica ack etc
> [1] http://docs.mongodb.org/manual/core/write-concern/
> [2]
> http://docs.mongodb.org/manual/tutorial/troubleshoot-replica-sets/#check-the-replication-lag
> [3] http://blog.mongolab.com/2013/03/replication-lag-the-facts-of-life/
> [4]
> http://docs.mongodb.org/manual/reference/command/replSetGetStatus/#dbcmd.replSetGetStatus
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