[HBASE-5689] Skipping RecoveredEdits may cause data loss

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 0.94.0
• Fix Version/s: 0.94.0
• Component/s: regionserver
• Hadoop Flags: Reviewed
• Assignee: Chunhui Shen
• Reporter: Chunhui Shen
• Created: 31/Mar/12 04:57
• Updated: 12/Oct/12 05:35
• Resolved: 07/Apr/12 15:32

Description

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

 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;
        }
      }