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https://issues.apache.org/jira/browse/HBASE-8698?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13720310#comment-13720310
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stack commented on HBASE-8698:
------------------------------
Looks like an improvement.
Can we do anything about HTable taking an HConnection. That seems way
convoluted and messes w/ layering.
Ditto on MetaScanner and then in HConnectionManager, we have metaScan (and over
in the catalog package other meta operators).
The MetaScanner doing a table open and close per op was done because notion is
that new HTable is cheap (and if not, lets fix). It also cleaned up
rationalizing whats going on in this class making sure we did clean up per call.
Yeah, more perversity in that a new HTable on construction creates another to
scan Meta.
I'd be +1 on commit.
> 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 <[email protected]>
> To:
> public-user-50Pas4EWwPEyzMRdD/IqWQ-wOFGN7rlS/M9smdsby/[email protected]
> 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-xmd5yjdbdmrexy1tmh2...@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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