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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-8698) potential thread creation in MetaScanner.metaScan
Date Thu, 25 Jul 2013 05:31:49 GMT

    [ https://issues.apache.org/jira/browse/HBASE-8698?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13719250#comment-13719250

Lars Hofhansl commented on HBASE-8698:

Also note that the ThreadPool in HTable is created with 1 core thread. So I believe that one
thread is created here unnecessarily.
I just ran TestFromClientSide with the HTable's threadpool just forced to null in metascan,
and it worked fine (metascan just calls getRowOrBefore and getScanner on the HTable object,
neither of which actually use the thread pool.

I'll make a patch tomorrow that will do two things:
# always force the HTable's thread pool used in metascan to null (saves the creation of the
pool itself and one unnecessary thread)
# allow the HConnection to be passed to metascan (optionally). So if called from an HConnection,
that connection can be used directly (saves expensive creation/caching of a new HConnection).

> potential thread creation in MetaScanner.metaScan
> -------------------------------------------------
>                 Key: HBASE-8698
>                 URL: https://issues.apache.org/jira/browse/HBASE-8698
>             Project: HBase
>          Issue Type: Bug
>          Components: Client
>    Affects Versions: 0.94.7
>            Reporter: Kireet Reddy
>            Assignee: Lars Hofhansl
> MetaScanner.metaScan() creates an instance of HTable per call. The constructur used creates
a new ThreadPoolExecutor. The executor itself will not create a thread unless it's pool is
used. I am not sure if the HTable instance in question ever uses it's pool. But if so, this
could become a big performance issue. Logging an issue at Lars's request. mail list chain
> ------------------------------------- 
> Indeed. That is bad.
> I cannot see a clean fix immediately, but we need to look at this.
> Mind filing a ticket, Kireet?
> -- Lars
> ________________________________
>  From: Kireet <kireet-Teh5dPVPL8nQT0dZR+AlfA@public.gmane.org>
> To: public-user-50Pas4EWwPEyzMRdD/IqWQ-wOFGN7rlS/M9smdsby/KFg@public.gmane.org 
> Sent: Friday, May 31, 2013 11:58 AM
> Subject: Re: HConnectionManager$HConnectionImplementation.locateRegionInMeta
> Even if I initiate the call via a pooled htable, the MetaScanner seems 
> to use a concrete HTable instance. The constructor invoked seems to 
> create a java ThreadPoolExecutor. I am not 100% sure but I think as long 
> as nothing is submitted to the ThreadPoolExecutor it won't create any 
> threads. I just wanted to confirm this was the case. I do see the 
> connection is shared.
> --Kireet
> On 5/30/13 7:38 PM, Ted Yu wrote:
> > HTablePool$**PooledHTable is a wrapper around HTable.
> >
> > Here is how HTable obtains a connection:
> >
> >     public HTable(Configuration conf, final byte[] tableName, final
> > ExecutorService pool)
> >         throws IOException {
> >       this.connection = HConnectionManager.getConnection(conf);
> >
> > Meaning the connection is a shared one based on certain key/value pairs
> > from conf.
> >
> > bq. So every call to batch will create a new thread?
> >
> > I don't think so.
> >
> > On Thu, May 30, 2013 at 11:28 AM, Kireet <kireet-Teh5dPVPL8nQT0dZR+AlfA-XMD5yJDbdMReXY1tMh2IBg@public.gmane.org>
> >
> >>
> >>
> >> Thanks, will give it a shot. So I should download 0.94.7 (latest stable)
> >> and run the patch tool on top with the backport? This is a little new to me.
> >>
> >> Also, I was looking at the stack below. From my reading of the code, the
> >> HTable.batch() call will always cause the prefetch call to occur, which
> >> will cause a new HTable object to get created. The constructor used in
> >> creating a new thread pool. So every call to batch will create a new
> >> thread? Or the HTable's thread pool never gets used as the pool is only
> >> used for writes? I think I am missing something but just want to confirm.
> >>
> >> Thanks
> >> Kireet

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