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https://issues.apache.org/jira/browse/HBASE-3845?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13090881#comment-13090881
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gaojinchao commented on HBASE-3845:
-----------------------------------
I verified the patch. I think it is ok.
I created a table(one regoin) and put a lot of data. The log said that seq is
continuous.
code :
// updateLock not needed for removing snapshot's entry
// Cleaning up of lastSeqWritten is in the finally clause because we
// don't want to confuse getOldestOutstandingSeqNum()
this.lastSeqWritten.remove(getSnapshotName(encodedRegionName));
Long seq = this.lastSeqWritten.get(encodedRegionName);
if (null != seq) {
LOG.error("gjc: end flush seq " + logSeqId + "current seq" + seq);
} else {
LOG.error("gjc: end flush seq " + logSeqId);
}
logs:
2011-08-25 04:11:50,807 ERROR org.apache.hadoop.hbase.regionserver.wal.HLog:
gjc:start flush seq495032
2011-08-25 04:11:50,808 ERROR org.apache.hadoop.hbase.regionserver.wal.HLog:
gjc:start flush seq495032current seq499908
2011-08-25 04:12:11,073 ERROR org.apache.hadoop.hbase.regionserver.wal.HLog:
gjc: end flush seq 499908current seq499909
2011-08-25 04:12:11,700 ERROR org.apache.hadoop.hbase.regionserver.wal.HLog:
gjc:start flush seq499909
2011-08-25 04:12:11,700 ERROR org.apache.hadoop.hbase.regionserver.wal.HLog:
gjc:start flush seq499909current seq505058
2011-08-25 04:12:58,532 ERROR org.apache.hadoop.hbase.regionserver.wal.HLog:
gjc: end flush seq 505058current seq505059
2011-08-25 04:12:58,784 ERROR org.apache.hadoop.hbase.regionserver.wal.HLog:
gjc:start flush seq505059
The logs before the patch:
2011-08-25 05:35:20,691 WARN org.apache.hadoop.hbase.regionserver.wal.HLog:
gjc:start seq679214
2011-08-25 05:35:20,940 WARN org.apache.hadoop.hbase.regionserver.wal.HLog:
gjc:end current seq679215
2011-08-25 05:36:19,024 WARN org.apache.hadoop.hbase.regionserver.wal.HLog:
gjc:start seq682145
2011-08-25 05:36:26,928 WARN org.apache.hadoop.hbase.regionserver.wal.HLog:
gjc:end current seq685931
2011-08-25 05:36:27,571 WARN org.apache.hadoop.hbase.regionserver.wal.HLog:
gjc:start seq686209
2011-08-25 05:36:36,311 WARN org.apache.hadoop.hbase.regionserver.wal.HLog:
gjc:end current seq690191
2011-08-25 05:36:36,768 WARN org.apache.hadoop.hbase.regionserver.wal.HLog:
gjc:start seq690244
2011-08-25 05:36:44,709 WARN org.apache.hadoop.hbase.regionserver.wal.HLog:
gjc:end current seq693566
2011-08-25 05:36:45,940 WARN org.apache.hadoop.hbase.regionserver.wal.HLog:
gjc:start seq694126
> data loss because lastSeqWritten can miss memstore edits
> --------------------------------------------------------
>
> Key: HBASE-3845
> URL: https://issues.apache.org/jira/browse/HBASE-3845
> Project: HBase
> Issue Type: Bug
> Affects Versions: 0.90.3
> Reporter: Prakash Khemani
> Assignee: ramkrishna.s.vasudevan
> Priority: Critical
> Fix For: 0.92.0
>
> Attachments:
> 0001-HBASE-3845-data-loss-because-lastSeqWritten-can-miss.patch,
> HBASE-3845-fix-TestResettingCounters-test.txt, HBASE-3845_1.patch,
> HBASE-3845_2.patch, HBASE-3845_4.patch, HBASE-3845_5.patch,
> HBASE-3845_6.patch, HBASE-3845__trunk.patch, HBASE-3845_branch90V1.patch,
> HBASE-3845_branch90V2.patch, HBASE-3845_trunk_2.patch,
> HBASE-3845_trunk_3.patch
>
>
> (I don't have a test case to prove this yet but I have run it by Dhruba and
> Kannan internally and wanted to put this up for some feedback.)
> In this discussion let us assume that the region has only one column family.
> That way I can use region/memstore interchangeably.
> After a memstore flush it is possible for lastSeqWritten to have a
> log-sequence-id for a region that is not the earliest log-sequence-id for
> that region's memstore.
> HLog.append() does a putIfAbsent into lastSequenceWritten. This is to ensure
> that we only keep track of the earliest log-sequence-number that is present
> in the memstore.
> Every time the memstore is flushed we remove the region's entry in
> lastSequenceWritten and wait for the next append to populate this entry
> again. This is where the problem happens.
> step 1:
> flusher.prepare() snapshots the memstore under
> HRegion.updatesLock.writeLock().
> step 2 :
> as soon as the updatesLock.writeLock() is released new entries will be added
> into the memstore.
> step 3 :
> wal.completeCacheFlush() is called. This method removes the region's entry
> from lastSeqWritten.
> step 4:
> the next append will create a new entry for the region in lastSeqWritten().
> But this will be the log seq id of the current append. All the edits that
> were added in step 2 are missing.
> ==
> as a temporary measure, instead of removing the region's entry in step 3 I
> will replace it with the log-seq-id of the region-flush-event.
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