Scanners can miss values riding the flush transition
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Key: HBASE-1219
URL: https://issues.apache.org/jira/browse/HBASE-1219
Project: Hadoop HBase
Issue Type: Bug
Reporter: stack
Priority: Blocker
Fix For: 0.19.1, 0.20.0
A scanner is made of a memcache scanner and a store files scanner. When a
flush happens, the memcache content gets turned into a store file and is added
to the list of already existing scanners. Currently the two scanners run
autonomously. Ben Maurer points out that if we were returning values out of
the memcache because they were of lower value than store file content, the
lower pegging that was going on in memcache doesn't make it across when we pick
up the memcache values in the flushed store file; we just keep on with whatever
the lowest among the store files that were in place before the flush.
Its a hard one to spot but should be easy to make a test for it.
Ben Maurer also points out that in StoreFileScanner, we should not register the
observer until after the scanners have been setup:
{code}
public StoreFileScanner(final Store store, final long timestamp,
final byte [][] targetCols, final byte [] firstRow)
throws IOException {
super(timestamp, targetCols);
this.store = store;
this.store.addChangedReaderObserver(this);
try {
openScanner(firstRow);
...
{code}
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