hbase-issues mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Anoop Sam John (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-13082) Coarsen StoreScanner locks to RegionScanner
Date Mon, 19 Oct 2015 16:23:05 GMT

    [ https://issues.apache.org/jira/browse/HBASE-13082?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14963558#comment-14963558
] 

Anoop Sam John commented on HBASE-13082:
----------------------------------------

bq.But one thing may be to check is that if we open but still the current scanner heap is
not reset will it have any impact on the current scan is what needs to be checked?  Because
during flush the reads can still be served from the snapshot
Yes during the process of flush (before the new file got committed) we will serve the scan
from the snapshot. Then we will call clearSnapshot which will remove the cells from memory.
 So we must include the new file into the heap. Else we can not release the snapshot until
the scanner is done. That will be too costly for us as we will tend to keep the cells in memory
for much longer time and also which is not in our control.
So we wont change the store file's heap during the scan is not really possible?

> 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