max_connections

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.

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

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.

Analyzing the Limits of Connection Scalability in Postgres - Microsoft Tech Community

 

On Sun, 30 May 2021 at 20:19, Vijaykumar Jain < > 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.

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