ramkrishna.s.vasudevan created HBASE-16643:
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Summary: Reverse scanner heap creation may not allow MSLAB closure
due to inproper 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
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.
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