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

["Stefan Egli (JIRA)" <ji...@apache.org>]

Stefan Egli created OAK-3976:
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             Summary: 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
             Fix For: 1.6


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 journal entries 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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