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https://issues.apache.org/jira/browse/HBASE-4485?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13131833#comment-13131833
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Amitanand Aiyer commented on HBASE-4485:
----------------------------------------
@Stack. The reason that I wanted to move notifyChangedReaders outside the lock
is to avoid a potential race condition where.
Thread A holds the lock for the Store.java, and wants to do
notifyChangedReaders holding the lock.
NotifyChangedReaders calls updateReaders on a StoreScanner -- Say scanner-B
Thread B is doing a seek on scanner-B so it holds a lock on the StoreScanner
object.
Thread B could now have to call getScanners() (which is now a synchronized
function in store) if the heap == null.
This could end up in a deadlock where Thread A has the lock for Store.java but
needs the lock for StoreScanner to get into updateReaders.
Thread B has the lock for StoreScanner.java but needs the lock for Store.java
to get into getScanners and finish the seek().
> Eliminate window of missing Data
> --------------------------------
>
> Key: HBASE-4485
> URL: https://issues.apache.org/jira/browse/HBASE-4485
> Project: HBase
> Issue Type: Sub-task
> Reporter: Amitanand Aiyer
> Assignee: Amitanand Aiyer
> Fix For: 0.94.0
>
> Attachments: 4485-v1.diff, 4485-v2.diff, 4485-v3.diff, 4485-v4.diff,
> repro_bug-4485.diff
>
>
> After incorporating v11 of the 2856 fix, we discovered that we are still
> having some ACID violations.
> This time, however, the problem is not about including "newer" updates; but,
> about missing older updates
> that should be including.
> Here is what seems to be happening.
> There is a race condition in the StoreScanner.getScanners()
> private List<KeyValueScanner> getScanners(Scan scan,
> final NavigableSet<byte[]> columns) throws IOException {
> // First the store file scanners
> List<StoreFileScanner> sfScanners = StoreFileScanner
> .getScannersForStoreFiles(store.getStorefiles(), cacheBlocks,
> isGet, false);
> List<KeyValueScanner> scanners =
> new ArrayList<KeyValueScanner>(sfScanners.size()+1);
> // include only those scan files which pass all filters
> for (StoreFileScanner sfs : sfScanners) {
> if (sfs.shouldSeek(scan, columns)) {
> scanners.add(sfs);
> }
> }
> // Then the memstore scanners
> if (this.store.memstore.shouldSeek(scan)) {
> scanners.addAll(this.store.memstore.getScanners());
> }
> return scanners;
> }
> If for example there is a call to Store.updateStorefiles() that happens
> between
> the store.getStorefiles() and this.store.memstore.getScanners(); then
> it is possible that there was a new HFile created, that is not seen by the
> StoreScanner, and the data is not present in the Memstore.snapshot either.
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