map_hash_bucket_size, map_hash_max_size, and memory usage

abstein2 nginx-forum at
Tue Nov 4 17:27:51 UTC 2014

I was hoping someone could clarify how exactly map_hash_bucket_size and
map_hash_max_size should be set and the impact it has on memory.

For map_hash_bucket_size, it says it should be a multiple of the processor's
line cache size. Under what circumstances does it make sense or would it be
necessary to move away from the default cache size?

For map_hash_max_size, is this just the maximum size of the hash? If so,
what is the metric: bytes? potential options? something else? Is it viewed
as the maximum size of all maps or just each specific map directive?

Also, do either of these values impact the memory that nginx uses? For
example, if I have 200 maps will ones with a higher map_hash_bucket_size use
more memory than one with a lower map_hash_bucket_size? Or a higher


Posted at Nginx Forum:,254572,254572#msg-254572

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