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https://issues.apache.org/jira/browse/OAK-1044?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13778594#comment-13778594
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Marcel Reutegger commented on OAK-1044:
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Another area where an improvement is possible is the background write
operation. MongoMK updates the nodes one by one, which means a request to
MongoDB for each of the nodes it updates. While MongoDB does not support batch
updates, it does have a way to update multiple documents, which match a given
query. This is something we might be able to leverage in this situation. The
background write usually updates multiple documents the same way. E.g. it sets
a new _lastRev to a given revision. Those updates with the same revision could
be packed together in a multi document update.
> Reduce traffic between MongoMK and MongoDB
> ------------------------------------------
>
> Key: OAK-1044
> URL: https://issues.apache.org/jira/browse/OAK-1044
> Project: Jackrabbit Oak
> Issue Type: Improvement
> Components: core, mongomk
> Reporter: Marcel Reutegger
>
> There is quite some redundant traffic going on between MongoMK and MongoDB,
> which can have a major impact on performance. One of the problems we already
> saw in the past when there are many changes on a node. The document in
> MongoDB grows and with every modification to the node the cost increases
> because MongoMK always requests the complete old document from MongoDB in the
> response. This is done for several reasons:
> 1) MongoMK looks at the returned old document and checks if the updates
> applied do not conflict.
> 2) MongoMK updates its cache with the old document and the updates it applied.
> Splitting the documents when they reach a certain size keeps the cost for an
> update within bounds, but most of the time the response just contains
> redundant information already present in MongoMK. E.g. when no other MongoMK
> instance modified the node, the returned document is the same as the one
> potentially already in the cache.
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