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From "David Snowsill (Jira)" <j...@apache.org>
Subject [jira] [Commented] (OAK-9112) High CPU IOWAIT on Mongo due to Oak background task
Date Mon, 29 Jun 2020 22:00:02 GMT

    [ https://issues.apache.org/jira/browse/OAK-9112?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17148165#comment-17148165
] 

David Snowsill commented on OAK-9112:
-------------------------------------

This issue can now be closed as the behavior is related to OAK-9115.

The behavior was caused when trying to perform Version GC when the node type is orderable
and the Mongo document is approaching 16M in size.

Once the node type was changed to NodeTypeConstants.NT_OAK_UNSTRUCTURED, Version GC did not
cause the high CPU IOWait described.

> High CPU IOWAIT on Mongo due to Oak background task
> ---------------------------------------------------
>
>                 Key: OAK-9112
>                 URL: https://issues.apache.org/jira/browse/OAK-9112
>             Project: Jackrabbit Oak
>          Issue Type: Bug
>          Components: mongomk
>    Affects Versions: 1.8.22
>         Environment: Mongo: 3.4.9
> Hosteding: Scalegrid
> Instance Size: Small
>            Reporter: David Snowsill
>            Priority: Major
>         Attachments: image-2020-06-15-19-41-04-852.png, image-2020-06-15-19-41-40-385.png
>
>
> Over the previous weekend, our existing application went from having 100,000 documents
in the "nodes" collection to 600,000 documents in the "nodes" collection. Since that time
there appears to be an Oak background task that commences running near 100% CPU IOWAIT and
heavy disk activity (read only). Please refer to charts below
> !image-2020-06-15-19-41-04-852.png!
> !image-2020-06-15-19-41-40-385.png!
> According to currentOp Mongo command, the queries being running look as follows:
> {code}
> { desc: "conn4944", threadId: "140061124310784", connectionId: 4944, client: "18.207.114.70:47008",
clientMetadata: \{ driver: { name: "mongo-java-driver", version: "unknown" }, os: \{ type:
"Linux", name: "Linux", architecture: "amd64", version: "4.4.115-k8s" }, platform: "Java/IcedTea/1.8.0_212-b04"
}, active: true, opid: 2215767, secs_running: 2, microsecs_running: \{ "$numberLong": "2280333"
}, op: "query", ns: "prod-content-service.nodes", query: \{ find: "nodes", filter: { _id:
"2:/prod/18d6b4d0-9ee8-4a06-804e-b3669f67dda8" }, limit: 1, singleBatch: true }, planSummary:
"IDHACK", numYields: 0, locks: \{ Global: "r", Database: "r", Collection: "r" }, waitingForLock:
false, lockStats: \{ Global: { acquireCount: { r: { "$numberLong": "2" } } }, Database: \{
acquireCount: { r: { "$numberLong": "1" } } }, Collection: \{ acquireCount: { r: { "$numberLong":
"1" } } } } }
> {code}
> and appears to be iterating over the entire collection.
> Can anyone provide any guidance on what is happening?



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