| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Jeff Davis <pgsql(at)j-davis(dot)com> |
| Cc: | Andres Freund <andres(at)2ndquadrant(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: group locking: incomplete patch, just for discussion |
| Date: | 2014-11-20 16:22:37 |
| Message-ID: | CA+TgmoY5FMn-OESA9WSbMNXu4DyQFUyVPdac72H-x5f2ytoVVQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Thu, Nov 20, 2014 at 4:21 AM, Jeff Davis <pgsql(at)j-davis(dot)com> wrote:
>> The
>> bad news, to borrow a phrase from Peter Geoghegan, is that it's an
>> unprincipled deadlock; a user confronted with the news that her
>> parallel scan has self-deadlocked will be justifiably dismayed.
>
> You seem to be raising this as a show-stopping problem, and I'm not
> convinced that it is.
Well, what I'm saying is that at very minimum we have to be able
detect deadlocks, and we have two plausible designs for avoiding that:
1. Modify the deadlock detector to know about lock groups.
2. Propagate pre-existing locks from the user backend to all the workers.
I initially proposed #1, but now I think #2 solves more of the
problems for less code.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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