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<div dir="ltr" data-setdir="false">The table is a mnesia table so ets:info/2 does not seem to work. I narrowed it down and it seemed to indeed be match_object just costing too much cpu time and perhaps locking the table. Ended up rewriting the table scanning algo (instead of match_object running around 100 * 2000 times, dump full table once and use Process dictionary to manipulate / filter / organize) and building a cache.</div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false">The runtime seems stable, it would still be interesting to diagnose those locks does mnesia have something similar to ets:info/2 ?</div><div><br></div>
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On Friday, January 17, 2020, 03:06:07 p.m. EST, Sverker Eriksson <sverker@erlang.org> wrote:
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<div><div id="yiv9762609011"><div><div>Have you tried without read_concurrency?</div><div><br clear="none"></div><div>What does ets:info(T, stats) after running for a while?</div><div><br clear="none"></div><div><br clear="none"></div><div><br clear="none"></div><div class="yiv9762609011yqt4591313111" id="yiv9762609011yqt10596"><div>On fre, 2020-01-17 at 19:27 +0000, Vans S wrote:</div><blockquote type="cite"><div class="yiv9762609011ydp848388f6yahoo-style-wrap" style="font-family:Helvetica Neue, Helvetica, Arial, sans-serif;font-size:13px;"><div></div>
<div><br clear="none"></div><div dir="ltr">I really want to measure this so I can have some facts, IMO the performance is degrading way too much for such a small workload. The frequency is these 3000 processes do 1 write to the table every 15 minutes, so about 3.3 writes per second. (as the processes start at different times). The processes match_object on the table about 30000 times per second, but in bursts, so 10 operations can happen in a single function then it would back off for a few seconds or more.</div>
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On Friday, January 17, 2020, 02:20:05 p.m. EST, Sverker Eriksson <sverker@erlang.org> wrote:
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<div><div id="yiv9762609011"><div><div class="yiv9762609011yqt4030086244" id="yiv9762609011yqtfd64394"><div>On fre, 2020-01-17 at 20:09 +0200, Led wrote:</div><blockquote type="cite"><div dir="ltr"><div class="yiv9762609011gmail_quote"><div class="yiv9762609011gmail_attr" dir="ltr"></div><blockquote type="cite"><div><div style="font-family:Helvetica Neue, Helvetica, Arial, sans-serif;font-size:13px;"><div dir="ltr">I am having some performance trouble in a system that does a few queries on a small ets table of around 10,000 records.<br clear="none"><br clear="none">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:<span>utilization</span>) is 100% and capped out on all 40 threads.<br clear="none"><br clear="none">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. <br clear="none"><br clear="none">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.<br clear="none"><br clear="none">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.</div></div></div><br clear="none"></blockquote></div><div><br clear="none"></div><div></div><span class="yiv9762609011gmail-tlid-translation yiv9762609011gmail-translation" lang="en"><span class="yiv9762609011gmail-" title="">You didn't specify parameters of your table.</span></span><br clear="none"><div><br clear="none"></div><div><br clear="none"></div></div></blockquote></div><div><br clear="none"></div><div>And what's the frequency of those inserts that you mention.</div><div><br clear="none"></div><div>ets:match_object is a read-only operation and should only inflict lock contention with other write operations, such as ets:insert.</div><div><br clear="none"></div><div><br clear="none"></div><div>/Sverker</div><div class="yiv9762609011yqt4030086244" id="yiv9762609011yqtfd57042"><div><br clear="none"></div></div></div></div></div>
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