locked up system using :ets.match_object

Led ledest@REDACTED
Fri Jan 17 19:09:52 CET 2020

> I am having some performance trouble in a system that does a few queries
> on a small ets table of around 10,000 records.
> Basically with around 500 concurrent processes, everything is fine, 1500 I
> start to notice some small degradation, at around 3000 concurrent processes
> the schedulers grind to a halt, TOP system CPU usage is around 50%, but
> Erlang scheduler usage (scheduler:utilization) is 100% and capped out on
> all 40 threads.
> I am guessing the schedulers are all waiting on locks on the ets table.  I
> thought match_object and ets was quite optimized these days, using R22, I
> am wondering if there is some synchronization/locking issues that could be
> addressed.  Because I mean at 3000 processes maybe hitting that table 10
> times per second on average, does not seem like much. 30k match_objects per
> second, with ongoing inserts.
> Also would there be a way to debug/pinpoint this is the exact issue?  I
> just did A/B testing where I turned off parts of the system, when I turned
> off the part that does the match_objects on the ETS table, the system ran
> fine and never deadlocked at 100% scheduler usage.  Its also hard to
> profile, as the system is so locked up the profiler barely runs.
> For now it seems the solution is to rework the architecture and put a
> second cached view ETS table, so the match_objects can be replaced with key
> lookups.  Which gets filled by a single process running that pulls via
> match_object from the main table and fills the cache.

You didn't specify parameters of your table.

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