[jira] [Commented] (OAK-3976) journal should support large(r) entries

["Julian Reschke (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/OAK-3976?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16096057#comment-16096057 ] 

Julian Reschke commented on OAK-3976:
-------------------------------------

trunk: [r1774094|http://svn.apache.org/r1774094]


> journal should support large(r) entries
> ---------------------------------------
>
>                 Key: OAK-3976
>                 URL: https://issues.apache.org/jira/browse/OAK-3976
>             Project: Jackrabbit Oak
>          Issue Type: Improvement
>          Components: documentmk
>    Affects Versions: 1.3.14
>            Reporter: Stefan Egli
>            Assignee: Vikas Saurabh
>             Fix For: 1.5.16, 1.6.0
>
>         Attachments: OAK-3976-1.patch, OAK-3976.patch
>
>
> Journal entries are created in the background write. Normally this happens every second. If for some reason there is a large delay between two background writes, the number of pending changes can also accumulate. Which can result in (arbitrary) large single journal entries (ie with large {{_c}} property).
> This can cause multiple problems down the road:
> * journal gc at this point loads 450 entries - and if some are large this can result in a very large memory consumption during gc (which can cause severe stability problems for the VM, if not OOM etc). This should be fixed with OAK-3001 (where we only get the id, thus do not care how big {{_c}} is)
> * before OAK-3001 is done (which is currently scheduled after 1.4) what we can do is reduce the delete batch size (OAK-3975)
> * background reads however also read the journal entries and even if OAK-3001/OAK-3975 are implemented the background read can still cause large memory consumption. So we need to improve this one way or another.



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