Strange mnesia behaviour

Dan Gudmundsson <>
Mon Aug 25 09:42:26 CEST 2003


Hmm

flush_downs cleans the msg queue, with alot msgs in it, it takes some 
time..

Can you email me the test program?

/Dan

Anders Nygren writes:
 > Hi
 > I have found a strange thing in mnesia. I was trying
 > to do some throughput measurement on a process.
 > 
 > My process does the following:
 > 1, receive one message
 > 2, make one mnesia:select
 > 3, send one message
 > 
 > My test was to send N identicat messages to my process
 > and measure the time it took to process all messages.
 > To my suprise the times grew non-linearly with N.
 > eprof shows that
 > N = 10 - > mnesia:flush_downs/0 is called 55 times
 > N = 100 -> mnesia:flush_downs/0 is called 5000 times
 > N = 4000 -> a whopping 4 million times.
 > 
 > Also if I run the test twice with 50 messages I get
 > 2500 mnesia:flush_downs, but when I run one test with
 > 100 messages there are 5000.
 > 
 > I the mnesia table has one record.
 > I am using a single node -> no distribution.
 > The table is type bag, disc_copy.
 > I am using R9C on Suse 8.2.
 > 
 > Is there something wrong with mnesia or is there 
 > something I dont understand?
 > 
 > /Anders
 > 
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