work_mem and shared_buffers question

[Ayub M <hiayub@xxxxxxxxx>]

1. shared_buffers - In a regular PostgreSQL installation, say I am allocating 25% of my memory to shared_buffers that means it leaves 75% for rest such as OS, page cache and work_mems etc. Is my understanding correct? If so, AWS Aurora for Postgres uses 75% of memory for shared_buffers, then it would leave just 25% for other things?
2. Does the memory specified for work_mem, fully gets allocated to all sessions irrespective of whether they do any sorting or hashing operations?

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Regards,

Ayub