hbase-issues mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "ramkrishna.s.vasudevan (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-13082) Coarsen StoreScanner locks to RegionScanner
Date Thu, 29 Oct 2015 11:06:27 GMT

    [ https://issues.apache.org/jira/browse/HBASE-13082?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14980263#comment-14980263
] 

ramkrishna.s.vasudevan commented on HBASE-13082:
------------------------------------------------

One interesting part while doing this is that of the Secondary replicas.  As per the idea
of read replicas the same underlying store file will be having a reader from the Secondary
region always opened. In the current code whenever we refreshStoreFiles we close the reader
that we think is no longer needed. So the archiving of the file if done by the primary region
will be successul. But now after this change we cannot do that because we need the file to
be available and only the compacted file cleaner can close the reader.  Now there are two
case
If suppose the compacted file cleaner has not closed the reader then the secondary region
will have a reader opened on the file and so any external archive option will fail. 
Similarly though the compacted file cleaner will close the reader and try to archive the compacted
file still if there is a reader opened by the secondary region this archival will fail. Anyway
the next cleaner thread will make it successful.  So may be need to see if there are any other
implications. 

> Coarsen StoreScanner locks to RegionScanner
> -------------------------------------------
>
>                 Key: HBASE-13082
>                 URL: https://issues.apache.org/jira/browse/HBASE-13082
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Lars Hofhansl
>            Assignee: ramkrishna.s.vasudevan
>         Attachments: 13082-test.txt, 13082-v2.txt, 13082-v3.txt, 13082-v4.txt, 13082.txt,
13082.txt, HBASE-13082.pdf, HBASE-13082_1_WIP.patch, HBASE-13082_2_WIP.patch, HBASE-13082_3.patch,
HBASE-13082_4.patch, gc.png, gc.png, gc.png, hits.png, next.png, next.png
>
>
> Continuing where HBASE-10015 left of.
> We can avoid locking (and memory fencing) inside StoreScanner by deferring to the lock
already held by the RegionScanner.
> In tests this shows quite a scan improvement and reduced CPU (the fences make the cores
wait for memory fetches).
> There are some drawbacks too:
> * All calls to RegionScanner need to be remain synchronized
> * Implementors of coprocessors need to be diligent in following the locking contract.
For example Phoenix does not lock RegionScanner.nextRaw() and required in the documentation
(not picking on Phoenix, this one is my fault as I told them it's OK)
> * possible starving of flushes and compaction with heavy read load. RegionScanner operations
would keep getting the locks and the flushes/compactions would not be able finalize the set
of files.
> I'll have a patch soon.



--
This message was sent by Atlassian JIRA
(v6.3.4#6332)

Mime
View raw message