[HBASE-15759] RegionObserver.preStoreScannerOpen() doesn't have acces to current readpoint

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 2.0.0
• Component/s: Coprocessors
• Labels: coprocessors
• Hadoop Flags: Reviewed

Release Note

The following RegionObserver method is deprecated and would no longer be called in hbase 2.0:

  public KeyValueScanner preStoreScannerOpen(final ObserverContext<RegionCoprocessorEnvironment> c,
      final Store store, final Scan scan, final NavigableSet<byte[]> targetCols,
      final KeyValueScanner s) throws IOException {

Instead, override this method:

  public KeyValueScanner preStoreScannerOpen(final ObserverContext<RegionCoprocessorEnvironment> c,
      final Store store, final Scan scan, final NavigableSet<byte[]> targetCols,
      final KeyValueScanner s, final long readPt) throws IOException {

• Assignee: Ted Yu
• Reporter: Marek Srank
• Created: 03/May/16 13:41
• Updated: 06/May/16 13:12
• Resolved: 06/May/16 13:12

Description

RegionObserver.preStoreScannerOpen() doesn't have acces to current readpoint. This is crucial e.g. when creating a new StoreScanner.

Although it is possible to obtain the readpoint via following workaround:

((HStore)store).getHRegion().getReadpoint(IsolationLevel.READ_COMMITTED)

...it presumes some knowledge of HBase internals and is not a clear option for user.

The problem was introduced in HBASE-9754, where readpoint was introduced as an argument to StoreScanner constructor, but wasn't passed to the preStoreScannerOpen() hook in HStore.getScanner().

In our case it led to bug, when we were incorrectly using smallestReadpoint() instead, which made coprocessor missing data in some cases [1].

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[1] http://mail-archives.apache.org/mod_mbox/hbase-dev/201604.mbox/%3CCAOUjMkwptCGacQ0d-4yOinDVBT%2Bbi2NOZee0fSbq%2Bk1R6V4-aw%40mail.gmail.com%3E