We caught this in an extended test run where IntegrationTestBigLinkedList failed with some missing keys.
The problem is that HRegion.replayRecoveredEdits() would return -1 if all the edits in the log file is skipped, which is true for example if the log file only contains a single compaction record (
HBASE-2231) or somehow the edits cannot be applied (column family deleted, etc).
The callee, HRegion.replayRecoveredEditsIfAny() only looks for the last returned seqId to decide whether a flush is necessary or not before opening the region, and discarding replayed recovered edits files.
Therefore, if the last recovered edits file is skipped but some edits from earlier recovered edits files are applied, the mandatory flush before opening the region is skipped. If the region server dies after this point before a flush, the edits are lost.
This is important to fix, though the sequence of events are super rare for a production cluster.