[GitHub] [accumulo] keith-turner opened a new issue #1730: Scans experience contention on global classloader lock when creating iterators

[GitBox <gi...@apache.org>]

keith-turner opened a new issue #1730:
URL: https://github.com/apache/accumulo/issues/1730


   **Describe the bug**
   In the past when running test against Accumulo w/ lots of concurrent scans and profiling tablets servers, the static synchronization around class loading was something that showed up in profiling data. Every scan uses class loaders to create iterators and this static synchronization causes locking contention between scans. 
   
   I think the following code is called to create iterator classes and is where the contention occurred.
   
   https://github.com/apache/accumulo/blob/9b537ca679da7f435cd34f79bf2939991b0e02d5/start/src/main/java/org/apache/accumulo/start/classloader/vfs/AccumuloVFSClassLoader.java#L112
   
   **Versions (OS, Maven, Java, and others, as appropriate):**
    - Affected version(s) of this project: [1.9.x,1.10.0,2.0.0]
   
   **Expected behavior**
   Scans should be able to create iterator classes w/o obtaining a global classloader lock.
   
   


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[GitHub] [accumulo] dlmarion commented on issue #1730: Scans experience contention on global classloader lock when creating iterators

[GitBox <gi...@apache.org>]

dlmarion commented on issue #1730:
URL: https://github.com/apache/accumulo/issues/1730#issuecomment-714565022


   In #1715 I modified how classes are loaded and all of the server side code uses [ClassLoaderUtil.loadClass()](https://github.com/apache/accumulo/pull/1715/files#diff-f8f44086240fb20a620240b6428fae288d4faf2851ddf348cf8e1c6e17edc693R25) which is not `synchonized`. If the table has a context defined, the `loadClass` operation is not `synchronized` either. Without a context the code still uses `AccumuloVFSClassLoader.loadClass` and will be `synchronized` until it's removal in a future release.


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