Efficient Insertions in Mnesia tables

Olivier BOUDEVILLE <>
Fri Nov 5 11:15:37 CET 2010


Hi,

We are trying to write (with mnesia:dirty_write) in a disc_only_copies 
Mnesia table (type: set, not fragmented, not replicated) records (ex: 60 
000 of them) and we observe that the insertion time is increasing as the 
table is increasingly crowded. This is not really a surprise but something 
we need to avoid. What we would like is to have constant (and preferably 
low) insertion times, like we had when writing directly to a file.

We tried to get as close as possible with the following settings and use:

                        % We want tables to be dumped less frequently from 
memory to disc,
                        % in order to buffer writings (default value is 
4):
                        ok = application:set_env( mnesia, dc_dump_limit, 1 
),

                        % Increases a lot (default value is 100) the 
maximum number of
                        % writes to the transaction log before a new dump 
is performed:
                        ok = application:set_env( mnesia, 
dump_log_write_threshold, 50000 ),

Over time we see the CPU load decrease steadily, the computer seems to 
spend most of its time fighting for locks.

We happen to be in a pretty favorable situation (only writes, no 
concurrent access to a given table). We chose disc_only_copies as there 
might be a large number of such tables and if they filled over time they 
could exhaust the RAM.

Is there anything we missed that would allow us (roughly) constant 
insertion times with Mnesia?

Thanks in advance for any hint,
Best regards,

Olivier.
---------------------------
Olivier Boudeville

EDF R&D : 1, avenue du Général de Gaulle, 92140 Clamart, France
Département SINETICS, groupe ASICS (I2A), bureau B-226
Office : +33 1 47 65 59 58 / Mobile : +33 6 16 83 37 22 / Fax : +33 1 47 
65 27 13



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