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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-8698) potential thread creation in MetaScanner.metaScan
Date Fri, 26 Jul 2013 04:31:49 GMT

    [ https://issues.apache.org/jira/browse/HBASE-8698?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13720393#comment-13720393
] 

Lars Hofhansl commented on HBASE-8698:
--------------------------------------

Yeah, the layer convolution is a pet peeve of mine. HBASE-6580 is attempt, maybe it is also
time to get closure on that one; would allow us to finally deprecate the HTablePool abomination
:)

Why does HTable call {{this.connection.locateRegion(tableName, HConstants.EMPTY_START_ROW);}}
upon creation (I had moved it into finishSetup a while ago, but it was called in the constructors
before). Is it to ensure the table exists? Or to allow prefetching of regions?

Let me mull this one over for another day or so, if I cannot think of any further improvement
I'll commit this.

                
> 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
>             Fix For: 0.98.0, 0.95.2, 0.94.11
>
>         Attachments: 8698-trunk.txt, 8698-trunk-v2.txt
>
>
> 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
below.
> ------------------------------------- 
> 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>
wrote:
> >
> >>
> >>
> >> 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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