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From lars hofhansl <la...@apache.org>
Subject Re: Question about memory chunk and waiting for memory to become free
Date Wed, 06 Sep 2017 04:37:38 GMT
Thanks James.
I'll file a jira.

      From: James Taylor <jamestaylor@apache.org>
 To: dev@phoenix.apache.org; lars hofhansl <larsh@apache.org> 
 Sent: Monday, September 4, 2017 9:11 AM
 Subject: Re: Question about memory chunk and waiting for memory to become free
   
Sure, Lars. As long as we throw an exception that'll cause a retry, it
seems fine to just fail it. We'll need some kind of synchronization around
the read/write of available memory member variable (or we can just use an
atomic long). Please update the docs here and indicate that
phoenix.query.maxGlobalMemoryWaitMs is deprecated as of 4.12:
http://phoenix.apache.org/tuning.html

On Sun, Sep 3, 2017 at 11:28 AM lars hofhansl <larsh@apache.org> wrote:

> Hi,
> just looking at MemoryChunk for various reasons.
> What I did not realize is that when no memory is currently available the
> implementation waits for memory to become available.The default wait time
> is 10s.
>
> This seems very dangerous to me. This can hang HBase handler threads at
> various points, especially when Phoenix is "busy" (I realize we're not
> talking about real memory here, but the effect is still that the HBase
> server threads would stall).
> HBase was designed with the assumption that individual RPCs do not tie up
> a handler thread for long. (The worst offender is a scan RPC that could
> scan up to a region's worth if a highly selective filter was passed). It's
> also possible that this is mostly used in asynchronous processing, although
> a quick scan of the code suggests that's not the case.
>
> It's possible that I'm missing something (in which case someone enlighten
> me please). I feel with wait time should be set to 0. I.e. we check whether
> there's memory available right now, if not we just fail the request and
> free the handler thread. I'd even argue we can remove the
> wait/synchronization code completely from MemoryChunk.
>
> Comments?
> -- Lars
>


   
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