| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Julien Rouhaud <julien(dot)rouhaud(at)dalibo(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Peter Geoghegan <pg(at)heroku(dot)com>, Noah Misch <noah(at)leadboat(dot)com>, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Magnus Hagander <magnus(at)hagander(dot)net>, Bruce Momjian <bruce(at)momjian(dot)us>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Rename max_parallel_degree? |
| Date: | 2016-06-14 17:07:25 |
| Message-ID: | CA+TgmobnFnqWd5P49K4SsBbA8jrLvVYqgoCGU-GQiSN8WSMt7Q@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tue, Jun 14, 2016 at 12:16 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> Of course, it would be nice if we could make these counters 64-bit
>> integers, but we can't, because we don't rely on 64-bit reads and
>> writes to be atomic on all platforms. So instead they'll have to be
>> uint32. That means they could wrap (if you really work at it) but
>> subtraction will still return the right answer, so it's OK.
>
> OK ...
>
>> If we
>> want to allow the number of parallel workers started to be available
>> for statistical purposes, we can keep to uint32 values for that
>> (parallel_register_count_lo and parallel_register_count_hi, for
>> example), and increment the second one whenever the first one rolls
>> over to zero.
>
> And that's going to be atomic how exactly?
The only process that can look at that structure without taking a lock
is the postmaster. And the postmaster would only examine
parallel_register_count_lo.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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