[erlang-questions] Test the system bottlenecks

[Solomon]

I test a web server run on a 24-core server. When server get a message, it would read/write mnesia and return a message to client. All of the mnesia tables are ram_copies and disc_copies.
I do a stress test and found that the heighest value of cpu load is only 900%, I get I/O load by iostat and it is idle, so I guess the system bottleneck is mnesia, but I found the reductions counter of mnesia's process are low.
Is my guess right?

[Gleb Peregud]

It is hard to answer with so little information. Few notes:
- Mnesia is a very complex piece of software - there is very many
processes and ETS tables. Both of them might be a serial bottleneck.
And some serializing process/ets can be short lived.
- If you use transactions for reads and writes, you are doing
serialization of all operations, hence low CPU usage is an obvious
result of this
- If you are doing dirty operations, there might be some other locks
which are being contented. Try recompiling erlang with lock counter
enabled and taking a look at results.

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