回复：[jira] [Updated] (HBASE-16643) Reverse scanner heap creation may not allow MSLAB closure due to improper ref counting of segments

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              String msg = "Results sent from server=" + noOfResults + ". But only got " + i                + " results completely at client. Resetting the scanner to scan again.";              LOG.error(msg);              throw new DoNotRetryIOException(msg);            }          } catch (IOException ioe) {            // We are getting IOE while retrieving the cells for Results.            // We have to scan for the same results again. Throwing DNRIOE as a client retry on the            // same scanner will result in OutOfOrderScannerNextException            LOG.error("Exception while reading cells from result."              + "Resetting the scanner to scan again.", ioe);            throw new DoNotRetryIOException("Resetting the scanner.", ioe);          }          cells.add(cellScanner.current());          System.out.println("ResponseConverter.getResults(1)--cells == "+ cells + "--j == " + j + "---noOfCells == " + noOfCells);        }        results[i] = Result.create(cells, null, response.getStale(), isPartial);        System.out.println("ResponseConverter.getResults(2)--cells == "+ cells + "--results[i] == " + results[i] + "---noOfCells == " + noOfCells);      } else {        // Result is pure pb.        results[i] = ProtobufUtil.toResult(response.getResults(i));        System.out.println("ResponseConverter.getResults(3)--results == " + results[i] + "--i == " + i);      }    }    return results; thank you very much, anoop, do you want to see this code, the exception should occur on the red mark line.
----- 原始邮件 -----
发件人："ramkrishna.s.vasudevan (JIRA)" <ji...@apache.org>
收件人：issues@hbase.apache.org
主题：[jira] [Updated] (HBASE-16643) Reverse scanner heap creation may not allow MSLAB closure due to improper ref counting of segments
日期：2016年09月23日 13点25分


     [ https://issues.apache.org/jira/browse/HBASE-16643?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
ramkrishna.s.vasudevan updated HBASE-16643:
-------------------------------------------
    Status: Open  (was: Patch Available)
> Reverse scanner heap creation may not allow MSLAB closure due to improper ref counting of segments
> --------------------------------------------------------------------------------------------------
>
>                 Key: HBASE-16643
>                 URL: https://issues.apache.org/jira/browse/HBASE-16643
>             Project: HBase
>          Issue Type: Bug
>            Reporter: ramkrishna.s.vasudevan
>            Assignee: ramkrishna.s.vasudevan
>            Priority: Critical
>             Fix For: 2.0.0
>
>         Attachments: HBASE-16643.patch, HBASE-16643_1.patch, HBASE-16643_2.patch, HBASE-16643_3.patch, HBASE-16643_4.patch, HBASE-16643_5.patch
>
>
> In the reverse scanner case,
> While doing 'initBackwardHeapIfNeeded' in MemstoreScanner for setting the backward heap, we do a 
> {code}
> if ((backwardHeap == null) && (forwardHeap != null)) {
>         forwardHeap.close();
>         forwardHeap = null;
>         // before building the heap seek for the relevant key on the scanners,
>         // for the heap to be built from the scanners correctly
>         for (KeyValueScanner scan : scanners) {
>           if (toLast) {
>             res |= scan.seekToLastRow();
>           } else {
>             res |= scan.backwardSeek(cell);
>           }
>         }
> {code}
> forwardHeap.close(). This would internally decrement the MSLAB ref counter for the current active segment and snapshot segment.
> When the scan is actually closed again we do close() and that will again decrement the count. Here chances are there that the count would go negative and hence the actual MSLAB closure that checks for refCount==0 will fail. Apart from this, when the refCount becomes 0 after the firstClose if any other thread requests to close the segment, then we will end up in corrupted segment because the segment could be put back to the MSLAB pool. 
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