[jira] [Commented] (OAK-4535) Analyze impact of Mongo isolation guarantees and Query result

["Chetan Mehrotra (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/OAK-4535?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15362319#comment-15362319 ] 

Chetan Mehrotra commented on OAK-4535:
--------------------------------------

Following types of queries are used with Mongo
# {_id > x and _id < y} - Look for documents with id in given range
# {_modified >= x } - Where _modified is timestamp and as a value it can only increase. Used in LastRevRecovery
# {_modified < x && _deletedOnce == true} - This is for version gc. Here we have sparse index on _deletedOnce (which is immutable property) and we have an index on _deletedOnce which is used
# {_id > x && _bin == true} - This is for blob gc. Here _bin is immutable property i.e. once set its not modified and we have a sparse index on it
# {_id > x and _id < y and _modified > z} - We have a compound index {_modified:1, _id:1} - Used in diffImpl and when changes done in persisted branch are reverted (again that uses diffImpl)



> Analyze impact of Mongo isolation guarantees and Query result
> -------------------------------------------------------------
>
>                 Key: OAK-4535
>                 URL: https://issues.apache.org/jira/browse/OAK-4535
>             Project: Jackrabbit Oak
>          Issue Type: Task
>          Components: mongomk
>            Reporter: Chetan Mehrotra
>            Assignee: Chetan Mehrotra
>             Fix For: 1.6
>
>
> As per [Mongo Isolation guarantees |https://docs.mongodb.com/manual/faq/concurrency/#what-isolation-guarantees-does-mongodb-provide]
> {quote}
> Reads may miss matching documents that are updated during the course of the read operation.
> {quote}
> This can result in some scenarios where query performed might miss out on some documents if that document gets modified while query is being execute.
> Aim of this task is to analyze the kind of queries current Oak uses with Mongo and see if current support from Mongo is sufficient for our needs



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