explanation about buffers and memory usage ... ?

hi,
just a simple question:
there are at least 4 types of buffers:
shared_buffers
sort_mem
effective_cache_size
geqo_pool_size

can you please tell me when all of this memory is used. what for, and
what's also important.
assuming that i have 16 backends spawned how much memory will it take?
shared_buffers are shared. but what about others? per backend?

See performance article on techdocs:

http://techdocs.postgresql.org

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