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https://issues.apache.org/jira/browse/BOOKKEEPER-685?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13778415#comment-13778415
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Rakesh R commented on BOOKKEEPER-685:
-------------------------------------
Thanks [~hustlmsp] for the detailed explanation.
bq.could you clarify it when you are saying it leads to trouble?
Could you please see the following execution sequence:
Th1 - compaction thread
Th2 - SyncThread
1) Th1: addEntry and sets flushed.set(false); // Consider that added entry is
the 'last entry' of the last ledger participated in compaction. After this,
compaction would move to flush.
2) Th2: onRotateEntryLog and sets flushed.set(true);
3) Th1: scannerFactory.flush(); // since it sees flushed==true, it will iterate
over the offsets and flush out
4) Th1: removeEntryLog
5) server crashed
In the above sequence, I could see a possible loss of 'last entry' which is not
flushed into the entry logger. Any thoughts?
CompactionScannerFactory.java
{code}
try {
// compaction finished, flush any outstanding offsets
scannerFactory.flush();
} catch (IOException ioe) {
LOG.error("Cannot flush compacted entries, skip removal", ioe);
return;
}
// offsets have been flushed, its now safe to remove the old entrylogs
for (Long l : toRemove) {
removeEntryLog(l);
}
{code}
> Race in compaction algorithm from BOOKKEEPER-664
> ------------------------------------------------
>
> Key: BOOKKEEPER-685
> URL: https://issues.apache.org/jira/browse/BOOKKEEPER-685
> Project: Bookkeeper
> Issue Type: Bug
> Reporter: Ivan Kelly
> Priority: Blocker
> Fix For: 4.2.2
>
>
> I discovered a race in the algorithm when I was forward porting to trunk.
> 1) Thread1: flushed.set(false)
> 2) Thread2: onRotateEntryLog() // flushed.set(true)
> 3) Thread1: entryLogger addEntry L123-E456
> 4) Thread1: offsets > max, waits for flushed, flushed is true(as set in 2),
> L123-E456 updated in ledger cache
> 5) T2: L123 flushed out of ledger cache
> 6) Crash
> This will possible lose 1 entry. I've only reasoned this, not observed it,
> but it can happen.
> The fix is pretty easy. EntryLoggerListener should notify with the point
> offset in the entry log it has synced as far as.
>
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