Monitor/expose utilization of shared memory (pgsm_max)

[percygrunwald]

Description

Hi, we would like to monitor the level of utilization of the shared memory allocated by the extension so we can know if pgsm_max needs to be increased or not. I couldn't find any reference for right-sizing the amount of shared memory given the query load or other factors, so we'd like to right-size it through monitoring the usage as a percentage of pgsm_max and increasing it if necessary.

Thank you.

Suggested solution

Provide a function that returns the memory usage by all the buckets in bytes, which could be compared to pgsm_max.

Additional context

We are currently using postgresql 12.

Happy to try to contribute this to the code if someone could give me a pointer about where I could start looking.

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