[jira] [Commented] (OAK-853) Many child nodes: Diffing causes many calls to the MicroKernel

["Jukka Zitting (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/OAK-853?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13675956#comment-13675956 ] 

Jukka Zitting commented on OAK-853:
-----------------------------------

As of revision 1489884 the above test case no longer causes any comparisons to fall back to the inefficient default implementation in {{AbstractNodeState.compareAgainstBaseState()}}.
                
> Many child nodes: Diffing causes many calls to the MicroKernel
> --------------------------------------------------------------
>
>                 Key: OAK-853
>                 URL: https://issues.apache.org/jira/browse/OAK-853
>             Project: Jackrabbit Oak
>          Issue Type: Improvement
>          Components: core
>            Reporter: Thomas Mueller
>         Attachments: OAK-853.patch
>
>
> Creating a flat hierarchy of the following form causes many calls to MicroKernel.getNodes and is thus slow.
> {code}
> for (int i = 0; i < 10000; i++) {
>     root.addNode("test" + i, "nt:folder");
>     if (i % 1000 == 0) {
>         session.save();
>     }
> }
> {code}
> As far as I see, this isn't just the case for MicroKernel based storage, but also for the SegmentNodeStore. The reason seems to be that the optimization for many child nodes in KernelNodeState.compareAgainstBaseState and SegmentNodeState.compareAgainstBaseState that avoids iterating over all children doesn't work. 
> The optimization uses:
> {code}
> if (base instanceof SegmentNodeState) ...
> if (base instanceof KernelNodeState) ...
> {code}
> Ideally, the instanceof should be avoided, but I'm not sure how to do that yet. Anyway, the problem is that "base" is a ModifiedNodeState so no optimization can be used.
> I was thinking, couldn't the ModifiedNodeState do a reverse diff in this case? That is, inside ModifiedNodeState.compareAgainstBaseState, check if the "base" parameter is a ModifiedNodeState, and the "base" field is not, then do a reverse diff, which would be efficient. (We should probably not use "base" for both the field name and the parameter; well that's a change for another time.)

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