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machinezone / mzmetrics

High performance Erlang metrics library
BSD 3-Clause "New" or "Revised" License
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advantages over ets counters? #2

Open benoitc opened 7 years ago

benoitc commented 7 years ago

what is the advantage of using mzmetrics comparedto simply using ets counters?

vlm commented 7 years ago

The ets counters are bottlenecked on a single mutex. If you're modifying a counter from multiple separate threads (e.g., the erlang processes that happen to be scheduled on separate threads), the access to the ets counter will get serialized through a single mutex, ensuing contention.

To mitigate contention, mzmetrics maintains separate counters for each metric, spreading them around the cache lines to avoid false sharing. This way, if you increment a counter from multiple threads, they will each increment their own counter, not contending on any shared resource.

The downside is that when you need to read the counter, you need to scan across different cachelines (up to the number of cores) to assemble the final counter value.

For workloads that are primarily write-heavy, mzmetrics can offer 10-100x speedup on counter operations. For the read-heavy counters, where counters get read comparatively frequently to the associated writes, the performance effect might be non-existent or slightly worse than ets counter.