max_connections

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max_connections

Vijaykumar Jain-2
I have a two dumb questions.

1)
I know the max_connections value change requires a restart.

I also read a thread, which says why it is the case, assuming it still holds true.

Jean Arnaud <Jean(dot)Arnaud(at)inrialpes(dot)fr> writes:
> I'm looking for a way to change the "max_connections" parameter without
> restarting the PostGreSQL database.

There is none. That's one of the parameters that determines shared
memory array sizes, and we can't change those on-the-fly.

regards, tom lane


Does that mean, if I set max_connections to 1000 users, but only intend to use 10 at max (via conn limit per role settings), what would be the perf difference compared to max_connections = 100 , but still using only 10 at max.

2)
can i for test purposes.compile src with a xid max value to 2^16 etc ? like with uint16 

Basically, I was trying to simulate xid wraparound, by creating an open transaction and an inactive replication slot, and then running a huge parallel loops to bump txid_current() to see what happens at 2B crossover. it takes forever on my slow laptop.
I do not see these in test scenarios, or could not find any.

as always, ignore if not relevant, or already discussed.
I am preparing for interviews, hence asking myself dumb questions :)

--
Thanks,
Vijay
Mumbai, India
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Re: max_connections

Vijaykumar Jain-2
ok, running too many connections without recycling has an overhead.
no wonder pgbouncer is all over as a sidecar :)

In case anyone is interested, this blog is a great read.

On Sun, 30 May 2021 at 20:19, Vijaykumar Jain <[hidden email]> wrote:
I have a two dumb questions.

1)
I know the max_connections value change requires a restart.

I also read a thread, which says why it is the case, assuming it still holds true.

Jean Arnaud <Jean(dot)Arnaud(at)inrialpes(dot)fr> writes:
> I'm looking for a way to change the "max_connections" parameter without
> restarting the PostGreSQL database.

There is none. That's one of the parameters that determines shared
memory array sizes, and we can't change those on-the-fly.

regards, tom lane


Does that mean, if I set max_connections to 1000 users, but only intend to use 10 at max (via conn limit per role settings), what would be the perf difference compared to max_connections = 100 , but still using only 10 at max.

2)
can i for test purposes.compile src with a xid max value to 2^16 etc ? like with uint16 

Basically, I was trying to simulate xid wraparound, by creating an open transaction and an inactive replication slot, and then running a huge parallel loops to bump txid_current() to see what happens at 2B crossover. it takes forever on my slow laptop.
I do not see these in test scenarios, or could not find any.

as always, ignore if not relevant, or already discussed.
I am preparing for interviews, hence asking myself dumb questions :)

--
Thanks,
Vijay
Mumbai, India


--
Thanks,
Vijay
Mumbai, India
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Re: max_connections

Vijaykumar Jain-2

On Fri, 4 Jun 2021 at 00:14, Vijaykumar Jain <[hidden email]> wrote:
ok, running too many connections without recycling has an overhead.
no wonder pgbouncer is all over as a sidecar :)

In case anyone is interested, this blog is a great read.

On Sun, 30 May 2021 at 20:19, Vijaykumar Jain <[hidden email]> wrote:
I have a two dumb questions.

1)
I know the max_connections value change requires a restart.

I also read a thread, which says why it is the case, assuming it still holds true.

Jean Arnaud <Jean(dot)Arnaud(at)inrialpes(dot)fr> writes:
> I'm looking for a way to change the "max_connections" parameter without
> restarting the PostGreSQL database.

There is none. That's one of the parameters that determines shared
memory array sizes, and we can't change those on-the-fly.

regards, tom lane


Does that mean, if I set max_connections to 1000 users, but only intend to use 10 at max (via conn limit per role settings), what would be the perf difference compared to max_connections = 100 , but still using only 10 at max.

2)
can i for test purposes.compile src with a xid max value to 2^16 etc ? like with uint16 

Basically, I was trying to simulate xid wraparound, by creating an open transaction and an inactive replication slot, and then running a huge parallel loops to bump txid_current() to see what happens at 2B crossover. it takes forever on my slow laptop.
I do not see these in test scenarios, or could not find any.

as always, ignore if not relevant, or already discussed.
I am preparing for interviews, hence asking myself dumb questions :)

--
Thanks,
Vijay
Mumbai, India


--
Thanks,
Vijay
Mumbai, India


--
Thanks,
Vijay
Mumbai, India