Scanner doesnt reset when a snapshot is created, could miss new updates into
the 'kvset' (active part)
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Key: HBASE-1738
URL: https://issues.apache.org/jira/browse/HBASE-1738
Project: Hadoop HBase
Issue Type: Bug
Affects Versions: 0.20.0
Reporter: ryan rawson
Fix For: 0.20.1
when a Scanner is created, it creates 2 MemStoreScanners on the kvset and the
snapshot (internal names of Memstore)... if the snapshot is originally empty,
it only creates the 1, for kvset. When the snapshot is created, the
outstanding Scanners now have a pointer to the tree that is now the snapshot,
but no pointer to the kvset.
When the flush completes, the scanner will reset the memstore scanners and
'see' the new values again.
If there is a large delay between snapshot and finalization of the flush, there
can be a large period of time a scanner doesnt see 'new' values that are being
inserted. the canonical 'bad' case where this can do things is the META
scanner, and we end up with double assignment.
The snapshot is really lightweight, it only takes out a small lock in memstore,
so im not sure there is an easy mechanism to hook to without building out a bit
more code or restructuring the memstore scanner.
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