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https://issues.apache.org/jira/browse/HBASE-1718?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12736384#action_12736384
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stack commented on HBASE-1718:
------------------------------
+1 on patch.
Its hard to test.
Here is my supposition as to why this might be responsible for hbase-1638.
Server crashes, its logs are split. The crashed servers regions are opened
anew and there are logs for them to replay.
The inner loop playing the reconstruction logs is this:
{code}
while (logReader.next(key, val)) {
maxSeqIdInLog = Math.max(maxSeqIdInLog, key.getLogSeqNum());
.....
// Check this edit is for me. Also, guard against writing the special
// METACOLUMN info such as HBASE::CACHEFLUSH entries
if (/* commented out for now - stack via jgray key.isTransactionEntry()
|| */
val.matchingFamily(HLog.METAFAMILY) ||
!Bytes.equals(key.getRegionName(), regioninfo.getRegionName()) ||
!val.matchingFamily(family.getName())) {
continue;
}
// Add anything as value as long as we use same instance each time.
reconstructedCache.add(val);
....
}
{code}
So, a value might clear the family checks and get added to the
reconstructionCache.
We call next again. The 'val' instance is up in reconstructionCache. The next
deserializes a new KV into same instance. The deserialized value might not
make it past family checks but its already in the reconstructionCache.
This would account for our adding a single value.
> Reuse of KeyValue during log replay could cause the wrong data to be used
> -------------------------------------------------------------------------
>
> Key: HBASE-1718
> URL: https://issues.apache.org/jira/browse/HBASE-1718
> Project: Hadoop HBase
> Issue Type: Bug
> Components: regionserver
> Affects Versions: 0.20.0
> Reporter: Jonathan Gray
> Priority: Blocker
> Fix For: 0.20.0
>
> Attachments: HBASE-1718-v1.patch
>
>
> Our meta table got a row key of METAROW in it. Hard to explain how it
> happened, but under code inspection stack found that we are reusing the same
> KV instance for each replayed key.
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