we found a suitable solution for our process we run every 5-6 hours a CLUSTER stement for our big table: this "lock" activities but allow us to recover all available space.
If you can tolerate the locks, that is fine, but it just doesn't seem like this should be necessary. A manual vacuum should get the job done with weaker locking. Did you try running a manual vacuum every 5-6 hours instead (it would probably not reclaim the space, but would make it available for reuse and so cap the steady-state size of the file, hopefully to about the same size as the max size under the CLUSTER regime)
When testing this task we discover another issues and that's why I'm coming back to you for your experience:
duting our process we run multiple simoultaneously "COPY... FROM" in order to load data into our table but a t the same time we run also "COPY ... TO" statement in parallel to export data for other clients.
We found that COPY .. TO queries sometimes are pending for more than 100 minutes and the destination file continues to be at 0 Kb. Can you advise me how to solve this issue?
Are your COPY ... FROM also blocking, just in a way you are not detecting (because there is no growing file to watch the size of)? What does pg_lock say?