saintstack commented on a change in pull request #762: HBASE-23157 WAL
unflushed seqId tracking may wrong when Durability.AS…
URL: https://github.com/apache/hbase/pull/762#discussion_r362705275
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File path:
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/SequenceIdAccounting.java
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@@ -356,9 +356,36 @@ Long startCacheFlush(final byte[] encodedRegionName,
final Map<byte[], Long> fam
return lowestUnflushedInRegion;
}
- void completeCacheFlush(final byte[] encodedRegionName) {
+ void completeCacheFlush(byte[] encodedRegionName, long maxFlushedSeqId) {
+ // This is a simple hack to avoid maxFlushedSeqId go backwards.
+ // The system works fine normally, but if we make use of
Durability.ASYNC_WAL and we are going
+ // to flush all the stores, the maxFlushedSeqId will be next seq id of the
region, but we may
+ // still have some unsynced WAL entries in the ringbuffer after we call
startCacheFlush, and
+ // then it will be recorded as the lowestUnflushedSeqId by the above
update method, which is
+ // less than the current maxFlushedSeqId. And if next time we only flush
the family with this
+ // unusual lowestUnflushedSeqId, the maxFlushedSeqId will go backwards.
+ // This is an unexpected behavior so we should fix it, otherwise it may
cause unexpected
+ // behavior in other area and then cause data loss maybe.
+ // The solution here is a bit hack but fine. Just replace the
lowestUnflushedSeqId with
+ // maxFlushedSeqId + 1 if it is lesser. Durability.ASYNC_WAL means we do
not care data loss for
Review comment:
Are the edits on the ring buffer that are outstanding meant to be part of
this flush or are they supposed to be counted in the next flush? Are you adding
the +1 so they are not part of the current flush?
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