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https://issues.apache.org/jira/browse/HBASE-5689?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13248421#comment-13248421
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stack commented on HBASE-5689:
------------------------------
@Ming (Hey, long time no hear from you).
On 1., yes, sounds good. I do not think 2. holds. It is more robust replaying
any file that is > 'current max seqid of the region' at least until we do more
thinking on this topic. The WAL split can be messy or just as bad, we can be
inventive around how we might split WALs and how we might write files to
replay.
> Skipping RecoveredEdits may cause data loss
> -------------------------------------------
>
> Key: HBASE-5689
> URL: https://issues.apache.org/jira/browse/HBASE-5689
> Project: HBase
> Issue Type: Bug
> Components: regionserver
> Affects Versions: 0.94.0
> Reporter: chunhui shen
> Assignee: chunhui shen
> Priority: Critical
> Fix For: 0.94.0
>
> Attachments: 5689-testcase.patch, 5689-v4.txt, HBASE-5689.patch,
> HBASE-5689.patch, HBASE-5689v2.patch, HBASE-5689v3.patch
>
>
> Let's see the following scenario:
> 1.Region is on the server A
> 2.put KV(r1->v1) to the region
> 3.move region from server A to server B
> 4.put KV(r2->v2) to the region
> 5.move region from server B to server A
> 6.put KV(r3->v3) to the region
> 7.kill -9 server B and start it
> 8.kill -9 server A and start it
> 9.scan the region, we could only get two KV(r1->v1,r2->v2), the third
> KV(r3->v3) is lost.
> Let's analyse the upper scenario from the code:
> 1.the edit logs of KV(r1->v1) and KV(r3->v3) are both recorded in the same
> hlog file on server A.
> 2.when we split server B's hlog file in the process of ServerShutdownHandler,
> we create one RecoveredEdits file f1 for the region.
> 2.when we split server A's hlog file in the process of ServerShutdownHandler,
> we create another RecoveredEdits file f2 for the region.
> 3.however, RecoveredEdits file f2 will be skiped when initializing region
> HRegion#replayRecoveredEditsIfAny
> {code}
> for (Path edits: files) {
> if (edits == null || !this.fs.exists(edits)) {
> LOG.warn("Null or non-existent edits file: " + edits);
> continue;
> }
> if (isZeroLengthThenDelete(this.fs, edits)) continue;
> if (checkSafeToSkip) {
> Path higher = files.higher(edits);
> long maxSeqId = Long.MAX_VALUE;
> if (higher != null) {
> // Edit file name pattern, HLog.EDITFILES_NAME_PATTERN: "-?[0-9]+"
> String fileName = higher.getName();
> maxSeqId = Math.abs(Long.parseLong(fileName));
> }
> if (maxSeqId <= minSeqId) {
> String msg = "Maximum possible sequenceid for this log is " +
> maxSeqId
> + ", skipped the whole file, path=" + edits;
> LOG.debug(msg);
> continue;
> } else {
> checkSafeToSkip = false;
> }
> }
> {code}
>
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