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From Michael Dürig (JIRA) <j...@apache.org>
Subject [jira] [Commented] (OAK-808) Significant performance issue in TargetImportHandler's prefix mapping handling
Date Thu, 02 May 2013 16:10:17 GMT

    [ https://issues.apache.org/jira/browse/OAK-808?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13647656#comment-13647656
] 

Michael Dürig commented on OAK-808:
-----------------------------------

Good catch, thanks for the patch. I'm not sure whether this is the right thing to do though
since it changes the semantics of {{TargetImportHandler#currentNamePathMapper()}}: without
the patch a caller would observe a certain mapping as it was when the name space map was returned
from {{currentNamePathMapper()}}, whereas with the patch a caller would observe the mapping
at it is at the time he looks into the map. 



                
> Significant performance issue in TargetImportHandler's prefix mapping handling
> ------------------------------------------------------------------------------
>
>                 Key: OAK-808
>                 URL: https://issues.apache.org/jira/browse/OAK-808
>             Project: Jackrabbit Oak
>          Issue Type: Bug
>          Components: jcr
>    Affects Versions: 0.7
>            Reporter: Lukas Eder
>         Attachments: Screen Shot YourKit Profiling Session.png, TargetImportHandler.java.patch
>
>
> While playing around with Oak, I have observed a significant performance bottleneck in

> {code}
> org.apache.jackrabbit.oak.jcr.xml.TargetImportHandler
> {code}
> The problem can be seen in the attached Screenshot taken from a Yourkit profiling session.
The TargetImportHandler contains a reference to a "documentContext" ListMultimap, which acts
like a stack of prefix - namespace mappings. To the outside, however, it is exposed as "documentPrefixMap",
a regular prefix - namespace mapping map, which only references the last namespace for a prefix.
> What's problematic here: "documentPrefixMap" is eagerly copied from "documentContext"
every time the latter is modified, which may happen a lot in upstream products, such as Adobe
CQ5. Instead, "documentPrefixMap" should be a Map view exposing the desired data. An example
implementation using Guava:
> {code}
> // Create this view once, in the constructor
> this.documentPrefixMap = Maps.transformValues(documentContext.asMap(),
>     new Function<Collection<String>, String>() {
>         @Override
>         public String apply(Collection<String> input) {
>             return Iterables.getLast(input, null);
>         }
>     });
> {code}
> The above implementation might work, as "documentPrefixMap" is a read-only view of the
"documentContext" map. More explicit, verbose implementations may prove to be even faster.
> Before I write a patch, please let me know what you think. Having a live view may of
course create concurrency issues, etc.

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