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_r362702196
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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
Review comment:
... maybe a slight hiccup for the async wal case -- maybe, given sync'ing to
HDFS is such an erratic affair -- but we will also be more 'correct' having
pushed out all in the ring buffer ahead of this flush sync w/o having to
rewrite their sequenceid.
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