Memory settings when running postgres in a docker container

Assuming a machine with:

* 16 CPU cores
* 64GB RAM

Set to 500 max connections

A tool like this: https://pgtune.leopard.in.ua/

Will output recommended settings:

max_connections = 500
shared_buffers = 16GB
effective_cache_size = 48GB
maintenance_work_mem = 2GB
checkpoint_completion_target = 0.9
wal_buffers = 16MB
default_statistics_target = 100
random_page_cost = 1.1
effective_io_concurrency = 200
work_mem = 8388kB
huge_pages = try
min_wal_size = 1GB
max_wal_size = 4GB
max_worker_processes = 16
max_parallel_workers_per_gather = 4
max_parallel_workers = 16
max_parallel_maintenance_workers = 4

And they basically use up all the memory of the machine.

16GB shared buffers, 48GB effective cache size, 8MB of work_mem for some
reason...

This seems rather extreme. I feel there should be free memory for
emergencies and monitoring solutions.

And then there's the fact that postgres on this machine will be run in a
docker container. Which, on Linux, receives 64MB of /dev/shm shared memory
by default, but can be increased.

I feel like I should probably actually lower my upper limit for memory,
regardless of what the machine actually has, so I can have free memory, and
also not bring the container process itself into danger.

Is it as straightforward as putting my limit on, say 20GB, and then giving
more /dev/shm to the container? Or is there more to consider?

Regards,
Koen De Groote

i dont get why you think all memroy will be used.
When you say
shared_buffers = 16GB
effective_cache_size = 48GB

...then this is using only 16GB for shared buffers.

The effective _cache_size doesn't cause any memory to.be allocated. It's
just a hint to optomizer ....

On Wed, 20 Nov 2024, 11:16 Koen De Groote, <kdg.dev@gmail.com> wrote:

Assuming a machine with:

* 16 CPU cores
* 64GB RAM

Set to 500 max connections

A tool like this: https://pgtune.leopard.in.ua/

Will output recommended settings:

max_connections = 500
shared_buffers = 16GB
effective_cache_size = 48GB
maintenance_work_mem = 2GB
checkpoint_completion_target = 0.9
wal_buffers = 16MB
default_statistics_target = 100
random_page_cost = 1.1
effective_io_concurrency = 200
work_mem = 8388kB
huge_pages = try
min_wal_size = 1GB
max_wal_size = 4GB
max_worker_processes = 16
max_parallel_workers_per_gather = 4
max_parallel_workers = 16
max_parallel_maintenance_workers = 4

And they basically use up all the memory of the machine.

16GB shared buffers, 48GB effective cache size, 8MB of work_mem for some
reason...

This seems rather extreme. I feel there should be free memory for
emergencies and monitoring solutions.

And then there's the fact that postgres on this machine will be run in a
docker container. Which, on Linux, receives 64MB of /dev/shm shared memory
by default, but can be increased.

I feel like I should probably actually lower my upper limit for memory,
regardless of what the machine actually has, so I can have free memory, and
also not bring the container process itself into danger.

Is it as straightforward as putting my limit on, say 20GB, and then
giving more /dev/shm to the container? Or is there more to consider?

Regards,
Koen De Groote