Major Description
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.
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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