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https://issues.apache.org/jira/browse/HBASE-588?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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stack updated HBASE-588:
------------------------
Attachment: 588-v3.patch
{code}
Add a ChangedReadersObserver interface. HStore notifies registered
observers when list of HStoreFile Readers changes -- at flush time
and at compaction time. Scanners are only current observers.
M src/test/org/apache/hadoop/hbase/MultiRegionTable.java
(getCacheFlushListern): Renamed as getFlushRequester
M src/java/org/apache/hadoop/hbase/regionserver/HStore.java
Added synchronizations on this.storefiles.
(activeScanners, newScannerLock): Removed. We no longer try to
block out scanners when compacting (Turns out same functionality
for blocking scanners is up in HRegion used around closing/split).
(changedReadersObservers): Added.
(updateReaders): New method that manages the insertion of new
reader on flush. Also calls new notifyChangedReadersObservers.
(notifyChagnedReadersObservers, addChangedReadersObserver,
deleteChangedReadersObservers): Added.
(completeCompaction): Previous deleting old store files, we'd
remove from this.storefiles and delete all in one step; now we
do the remove first, notify all observers of readers, and then
do the delete so observers have a chance to clean up any old
references to files about to be deleted. Removed all the lockout
of new scanner creation and wait on old scanners to come int.
(updateActiveScanners): Removed.
(getStorefiles): Accessor. Added.
M src/java/org/apache/hadoop/hbase/regionserver/StoreFileScanner.java
Added implementation of new ChangedReadersObserver interface.
Added a lock that we hold when 'nexting' and when changing the
set of readers out from under the scanner.
Changed the constructor moving bulk into new openReaders method
that we reuse when list of Readers changes.
(next): Moved head of this method into new getNextViableRow (used
to be called chosenRow and chosenTimestamp). New method returns
simple datastructure of row and timestamp (ViableRow).
(close): On close, remove ourselves as ChangedReadersObserver (we
added ourselves in the constructor).
(updateReaders): Changed the set of Readers out from under the
Scanner.
A src/java/org/apache/hadoop/hbase/regionserver/ChangedReadersObserver.java
Added.
M src/java/org/apache/hadoop/hbase/regionserver/Flusher.java
Changed name of the interface we implement from CacheFlushListener to
FlushRequester.
D src/java/org/apache/hadoop/hbase/regionserver/CacheFlushListener.java
Renamed as FlushRequester.
M src/java/org/apache/hadoop/hbase/regionserver/HStoreScanner.java
Remove update of activeScanners.
A src/java/org/apache/hadoop/hbase/regionserver/FlushRequester.java
Added. Rename of CacheFlushListener.
M src/java/org/apache/hadoop/hbase/regionserver/HRegionServer.java
Renamed method getCacheFlushListener as getFlushRequester.
M src/java/org/apache/hadoop/hbase/regionserver/HAbstractScanner.java
Formatting.
M src/java/org/apache/hadoop/hbase/regionserver/HRegion.java
CacheFlushListener was renamed as FlushListener.
{code}
> Still a 'hole' in scanners, even after HBASE-532
> ------------------------------------------------
>
> Key: HBASE-588
> URL: https://issues.apache.org/jira/browse/HBASE-588
> Project: Hadoop HBase
> Issue Type: Bug
> Reporter: stack
> Priority: Blocker
> Fix For: 0.1.2
>
> Attachments: 588-v2.patch, 588-v3.patch, 588.patch
>
>
> Before HBASE-532, as soon as a flush started, we called snapshot. Snapshot
> used to copy current live memcache into a 'snapshot' TreeMap inside in
> Memcache. This snapshot TreeMap was an accumulation of all snapshots since
> last flush. Whenever we took out a scanner, we'd do a copy of this snapshot
> into a new backing map carried by the scanner (Every outstanding Scanner had
> complete copy). Memcache snapshots were cleared when a flush started.
> Flushing could take near no time to up to tens of seconds during which an
> scanners taken out meantime would not see the edits in the snapshot currently
> being flushed and gets or getFull would also return incorrect answers because
> the content of the snapshot was not available to them.
> HBASE-532 made it so the snapshot was available until flush was done -- until
> a file had made it out to disk. This fixed gets and getFull and any scanners
> taken out during flushing. But there is still a hole. Any outstanding
> scanners will be going against the state of Store Readers at time scanner was
> opened; they will not see the new flush file.
> Chatting about this on IRC, Jim suggests that we pass either memcache or
> current snapshot to each Scanner (Pass the snapshot if not empty). The
> notion is that the Scanner would hold on to the Scanner reference should it
> be cleared by flushing. Upside is that scanner wouldn't have to be concerned
> with the new flush that has been put out to disk. Downsides are that Scanner
> data could be way stale if for instance the memcache was near to flushing but
> we hadn't done it yet. And we wouldn't be clearing the snapshot promptly so
> would be some memory pressure.
> Another suggestion is that flushing send an event. Listeners such as
> outstanding scanners would notice event and open the new Reader. Would have
> to skip forward in the new Reader to catch up with the current set but
> shouldn't be bad. Same mechanism could be used to let compactions be moved
> into place while scanners were outstanding closing down all existing readers
> skipping to the current 'next' location in the new compacted store file.
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