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https://issues.apache.org/jira/browse/OAK-333?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13526282#comment-13526282
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Thomas Mueller commented on OAK-333:
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Indexing the hash of the path would be very bad for performance, because it
would cause nodes that are logically close to each other (have a similar path)
to be distributed over the whole (possibly sharded) repository. See also
Shard Keys:
http://docs.mongodb.org/manual/core/sharding-internals/#sharding-internals-shard-keys
:
Query Isolation:
http://docs.mongodb.org/manual/core/sharding-internals/#sharding-shard-key-query-isolation
"The fastest queries in a sharded environment are those that mongos will route
to a single shard"
Now, let's assume we use the hash code of the path as the shard key (and not
the path). If we do that, each query to retrieve a number of nodes with a given
depth (let's say depth 3) will have to first read the parent node, then for
each child node read the child node, and so on. That's almost n queries (where
n is the number of returned nodes)!
When using the path as the shared key, it's just one query (path like '/.../%'
and depth between 3 and 6), which is routed to just one shard normally, because
all nodes are stored in the same shard.
> 1000 character path limit in MongoMK
> ------------------------------------
>
> Key: OAK-333
> URL: https://issues.apache.org/jira/browse/OAK-333
> Project: Jackrabbit Oak
> Issue Type: Bug
> Components: mk, mongomk
> Affects Versions: 0.5
> Reporter: Mete Atamel
> Assignee: Mete Atamel
> Priority: Minor
> Attachments: OAK-333.patch
>
>
> In an infinite loop try to add nodes one under another to have N0/N1/N2...NN.
> At some point, the current parent node will not be found and the current
> commit will fail. I think this happens when the path length exceeds 1000
> characters. Is this enough for a path? I was able to create this way only 222
> levels in the tree (and my node names were really short N1, N2 ...)
> There's an automated tests for this: NodeExistsCommandMongoTest.testTreeDepth
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