Re: [Postgres-xc-general] failed to find proc - increasing numProcs

[Aaron J. <aja...@re...>]

Yes, I was able to isolate it down to the test clause of the loop evaluation at the end of ProcArray.  To ensure I wasn't looking at volatile values, I copied the values used during the test so they weren't subject to changes to memory.  I'll put the exact scenario back together again for you and post it here.

It was pretty obvious when the loop began to exit prematurely and post-test values indicated that things which should be truths weren't (e.g. 1 < 3 = 1 but the test was returning 0).

I will have an answer by the weekend.

Aaron

________________________________
From: 鈴木 幸市 [ko...@in...]
Sent: Sunday, April 13, 2014 7:55 PM
To: Aaron Jackson
Cc: pos...@li...
Subject: Re: [Postgres-xc-general] failed to find proc - increasing numProcs

Thank you Aaron for the detailed analysis.   As long as the issue is just for XC, we need a fix for it to work correctly regardless the compiler optimization.

Did to locate where such wrong estimation takes place?   And what compilation option did you use?

They are very helpful.

Best;
---
Koichi Suzuki

2014/04/12 11:40、Aaron Jackson <aja...@re...<mailto:aja...@re...>> のメール：

It appears that problem is a compiler optimization issue.  I narrowed the issue down to the loop at the end of the ProcArrayRemove method.  I'm not entirely sure why, but the compiler generated code that evaluates the test block of the loop improperly.  Since changing the compiler options, the problem has been resolved.

Aaron

________________________________
From: Aaron Jackson [aja...@re...<mailto:aja...@re...>]
Sent: Friday, April 11, 2014 1:07 AM
To: pos...@li...<mailto:pos...@li...>
Subject: Re: [Postgres-xc-general] failed to find proc - increasing numProcs

I forgot to mention that if I injected a context switch (sleep(0) did the trick as did an elog statement) during the test in the ProcArrayRemove, that it no longer failed.  Hopefully that will help in understanding the reasons why that may have triggered the ProcArrayRemove to succeed.
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