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From "John Sirois" <jsir...@apache.org>
Subject Re: Review Request 42613: Enable READ COMMITTED transaction isolation.
Date Thu, 21 Jan 2016 20:42:43 GMT


> On Jan. 21, 2016, 1:28 p.m., John Sirois wrote:
> > IIUC the MVCC capabilities in 1.4+ should prevent table locks on all but DDL stuff.
> 
> John Sirois wrote:
>     Hmm - more to the story: "If MVCC is enabled, changing the lock mode (LOCK_MODE)
has no effect." ... Maybe turning on MVCC is worth some perf tests or have you already been
down that road?
> 
> Maxim Khutornenko wrote:
>     I suggest a cautios approach to enabling MVCC as our previous experience showed unacceptable
performance with any meaningful amounts of data.
> 
> Bill Farner wrote:
>     Bigger caution for me is that MVCC is considered beta in H2.

The beta bit is not at all clear to me.  If I read like a lawyer, I _think_ I agree, but I
don;t find this all that clear!:
> The MVCC mode is enabled by default in version 1.4.x, with the default MVStore storage
engine. MVCC is disabled by default when using the PageStore storage engine (which is the
default in version 1.3.x). The following applies when using the PageStore storage engine:
The MVCC feature is not fully tested yet.


- John


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This is an automatically generated e-mail. To reply, visit:
https://reviews.apache.org/r/42613/#review115684
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On Jan. 21, 2016, 1:40 p.m., Bill Farner wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://reviews.apache.org/r/42613/
> -----------------------------------------------------------
> 
> (Updated Jan. 21, 2016, 1:40 p.m.)
> 
> 
> Review request for Aurora, John Sirois and Zameer Manji.
> 
> 
> Bugs: AURORA-1580
>     https://issues.apache.org/jira/browse/AURORA-1580
> 
> 
> Repository: aurora
> 
> 
> Description
> -------
> 
> Proposing this as the minimal fix for AURORA-1580.  I think it's wise, however, to look
towards the alternative approach i described in that ticket for simplicity and performance
gains.
> 
> I'd like to note that after this change, it will be important to treat long-running transactions
carefully.  It will be important to avoid transactions block others by writing (locking a
table) and subsequently doing other lengthy work.
> 
> 
> Diffs
> -----
> 
>   src/main/java/org/apache/aurora/scheduler/storage/db/DbModule.java 2b3ee7bf6f7801c140f921b25f78daf6d320098a

>   src/main/resources/org/apache/aurora/scheduler/storage/db/TaskMapper.xml e689cfeda39e1f065ed29c61a23376512df8f3aa

>   src/test/java/org/apache/aurora/scheduler/storage/AbstractTaskStoreTest.java 3dba286556ab6ea34b7fdd38508a164c902d9d17

> 
> Diff: https://reviews.apache.org/r/42613/diff/
> 
> 
> Testing
> -------
> 
> 
> Thanks,
> 
> Bill Farner
> 
>


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