[jira] [Created] (LUCENE-4989) Hanging on DocumentsWriterStallControl.waitIfStalled forever

["Jessica Cheng (JIRA)" <ji...@apache.org>]

Jessica Cheng created LUCENE-4989:
-------------------------------------

             Summary: Hanging on DocumentsWriterStallControl.waitIfStalled forever
                 Key: LUCENE-4989
                 URL: https://issues.apache.org/jira/browse/LUCENE-4989
             Project: Lucene - Core
          Issue Type: Bug
          Components: core/index
    Affects Versions: 4.1
         Environment: Linux 2.6.32
            Reporter: Jessica Cheng


In an environment where our underlying storage was timing out on various operations, we find all of our indexing threads eventually stuck in the following state (so far for 4 days):

"Thread-0" daemon prio=5 Thread id=556  WAITING
	at java.lang.Object.wait(Native Method)
	at java.lang.Object.wait(Object.java:503)
	at org.apache.lucene.index.DocumentsWriterStallControl.waitIfStalled(DocumentsWriterStallControl.java:74)
	at org.apache.lucene.index.DocumentsWriterFlushControl.waitIfStalled(DocumentsWriterFlushControl.java:676)
	at org.apache.lucene.index.DocumentsWriter.preUpdate(DocumentsWriter.java:301)
	at org.apache.lucene.index.DocumentsWriter.updateDocument(DocumentsWriter.java:361)
	at org.apache.lucene.index.IndexWriter.updateDocument(IndexWriter.java:1484)
	at ...

I have not yet enabled detail logging and tried to reproduce yet, but looking at the code, I see that DWFC.abortPendingFlushes does

        try {
          dwpt.abort();
          doAfterFlush(dwpt);
        } catch (Throwable ex) {
          // ignore - keep on aborting the flush queue
        }

(and the same for the blocked ones). Since the throwable is ignored, I can't say for sure, but I've seen DWPT.abort thrown in other cases, so if it does throw, we'd fail to call doAfterFlush and properly decrement flushBytes. This can be a problem, right? Is it possible to do this instead:

        try {
          dwpt.abort();
        } catch (Throwable ex) {
          // ignore - keep on aborting the flush queue
        } finally {
          try {
            doAfterFlush(dwpt);
          } catch (Throwable ex2) {
            // ignore - keep on aborting the flush queue
          }
        }

It's ugly but safer. Otherwise, maybe at least add logging for the throwable just to make sure this is/isn't happening.

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