| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Re: [COMMITTERS] pgsql: Introduce group locking to prevent parallel processes from deadl |
| Date: | 2016-02-14 22:26:23 |
| Message-ID: | 30320.1455488783@sss.pgh.pa.us |
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| Lists: | pgsql-committers pgsql-hackers |
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Sun, Feb 14, 2016 at 1:33 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> pgprocno of the specific PGPROC, or of the group leader? If it's
>> the former, I'm pretty suspicious that there are deadlock and/or
>> linked-list-corruption hazards here. If it's the latter, at least
>> the comments around this are misleading.
> Leader. The other way would be nuts.
... and btw, either BecomeLockGroupMember() has got this backwards, or
I'm still fundamentally confused.
Also, after fixing that it would be good to add a comment explaining why
it's not fundamentally unsafe for BecomeLockGroupMember() to examine
leader->pgprocno without having any relevant lock. AFAICS, that's only
okay because the pgprocno fields are never changed after InitProcGlobal,
even when a PGPROC is recycled.
regards, tom lane
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