Обсуждение: BUG #18343: Incorrect description in postgresql.conf for max_parallel_workers_per_gather
BUG #18343: Incorrect description in postgresql.conf for max_parallel_workers_per_gather
От
PG Bug reporting form
Дата:
The following bug has been logged on the website:
Bug reference: 18343
Logged by: Christopher Kline
Email address: kline.christopher@gmail.com
PostgreSQL version: 14.11
Operating system: Windows 10 x64
Description:
In the default postgresql.conf that is generated, there are the following
lines:
#max_worker_processes = 8 # (change requires restart)
#max_parallel_workers_per_gather = 2 # taken from max_parallel_workers
<<<<<<<<<<<<<<<<<<<<<<<< THIS
#max_parallel_maintenance_workers = 2 # taken from max_parallel_workers
max_parallel_workers = 8 # maximum number of max_worker_processes that
# can be used in parallel operations
it indicates that the default value is taken from whatever
max_parallel_workers is. However, if I start postgresql with those settings
and issue a query of
SELECT setting, unit FROM pg_settings WHERE name =
'max_parallel_workers_per_gather'
the result I get is '2', not '8'.
This leads me to believe that either there is a bug in the code that's not
setting the correct default, or the comment in postgresql.conf is incorrect.
PG Bug reporting form <noreply@postgresql.org> writes:
> In the default postgresql.conf that is generated, there are the following
> lines:
> #max_worker_processes = 8 # (change requires restart)
> #max_parallel_workers_per_gather = 2 # taken from max_parallel_workers
> <<<<<<<<<<<<<<<<<<<<<<<< THIS
> #max_parallel_maintenance_workers = 2 # taken from max_parallel_workers
> max_parallel_workers = 8 # maximum number of max_worker_processes that
> # can be used in parallel operations
> it indicates that the default value is taken from whatever
> max_parallel_workers is.
No, you're misreading it. There's no magic connection between these
two settings. What the comment means to say is that the per-gather
worker processes come out of a pool of at most max_parallel_workers
processes. Perhaps another wording would be better, but we don't have
a lot of space here --- any thoughts?
regards, tom lane
Re: BUG #18343: Incorrect description in postgresql.conf for max_parallel_workers_per_gather
От
"David G. Johnston"
Дата:
On Thu, Feb 15, 2024 at 8:55 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
PG Bug reporting form <noreply@postgresql.org> writes:
> In the default postgresql.conf that is generated, there are the following
> lines:
> #max_worker_processes = 8 # (change requires restart)
> #max_parallel_workers_per_gather = 2 # taken from max_parallel_workers
> <<<<<<<<<<<<<<<<<<<<<<<< THIS
> #max_parallel_maintenance_workers = 2 # taken from max_parallel_workers
> max_parallel_workers = 8 # maximum number of max_worker_processes that
> # can be used in parallel operations
> it indicates that the default value is taken from whatever
> max_parallel_workers is.
No, you're misreading it. There's no magic connection between these
two settings. What the comment means to say is that the per-gather
worker processes come out of a pool of at most max_parallel_workers
processes. Perhaps another wording would be better, but we don't have
a lot of space here --- any thoughts?
max_parallel workers = 8 # allocated from max_worker_processes
max_parallel_*_workers = N # allocated from max_parallel_workers
or maybe "consumed from ..."
Or
max_parallel_*_workers = N # capped at max_parallel_workers
The last one turns a process-oriented description into a constraint, the latter seems to fit better in a config file.
David J.
Re: BUG #18343: Incorrect description in postgresql.conf for max_parallel_workers_per_gather
От
Christopher Kline
Дата:
Thank you all for the clarification. I like David Johnston's suggestion of
# capped at max_parallel_workers
That clearly defines the constraint.
On Thu, Feb 15, 2024 at 11:10 AM David G. Johnston <david.g.johnston@gmail.com> wrote:
On Thu, Feb 15, 2024 at 8:55 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:PG Bug reporting form <noreply@postgresql.org> writes:
> In the default postgresql.conf that is generated, there are the following
> lines:
> #max_worker_processes = 8 # (change requires restart)
> #max_parallel_workers_per_gather = 2 # taken from max_parallel_workers
> <<<<<<<<<<<<<<<<<<<<<<<< THIS
> #max_parallel_maintenance_workers = 2 # taken from max_parallel_workers
> max_parallel_workers = 8 # maximum number of max_worker_processes that
> # can be used in parallel operations
> it indicates that the default value is taken from whatever
> max_parallel_workers is.
No, you're misreading it. There's no magic connection between these
two settings. What the comment means to say is that the per-gather
worker processes come out of a pool of at most max_parallel_workers
processes. Perhaps another wording would be better, but we don't have
a lot of space here --- any thoughts?max_parallel workers = 8 # allocated from max_worker_processesmax_parallel_*_workers = N # allocated from max_parallel_workersor maybe "consumed from ..."Ormax_parallel_*_workers = N # capped at max_parallel_workersThe last one turns a process-oriented description into a constraint, the latter seems to fit better in a config file.David J.
Christopher Kline <kline.christopher@gmail.com> writes:
> Thank you all for the clarification. I like David Johnston's suggestion of
> # capped at max_parallel_workers
> That clearly defines the constraint.
I was thinking perhaps "# limited by max_parallel_workers"
or something like that. "Capped at" isn't phraseology we
use elsewhere.
regards, tom lane
Re: BUG #18343: Incorrect description in postgresql.conf for max_parallel_workers_per_gather
От
"David G. Johnston"
Дата:
On Thu, Feb 15, 2024 at 10:31 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
Christopher Kline <kline.christopher@gmail.com> writes:
> Thank you all for the clarification. I like David Johnston's suggestion of
> # capped at max_parallel_workers
> That clearly defines the constraint.
I was thinking perhaps "# limited by max_parallel_workers"
or something like that. "Capped at" isn't phraseology we
use elsewhere.
"limited by" is indeed better IMO as well.
David J.
Re: BUG #18343: Incorrect description in postgresql.conf for max_parallel_workers_per_gather
От
Christopher Kline
Дата:
Agreed.
On Thu, Feb 15, 2024 at 2:42 PM David G. Johnston <david.g.johnston@gmail.com> wrote:
On Thu, Feb 15, 2024 at 10:31 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:Christopher Kline <kline.christopher@gmail.com> writes:
> Thank you all for the clarification. I like David Johnston's suggestion of
> # capped at max_parallel_workers
> That clearly defines the constraint.
I was thinking perhaps "# limited by max_parallel_workers"
or something like that. "Capped at" isn't phraseology we
use elsewhere."limited by" is indeed better IMO as well.David J.
Christopher Kline <kline.christopher@gmail.com> writes:
> On Thu, Feb 15, 2024 at 2:42 PM David G. Johnston <
> david.g.johnston@gmail.com> wrote:
>> "limited by" is indeed better IMO as well.
> Agreed.
Sold, I'll make it so.
regards, tom lane