mnesia cluster limits

Dan Gudmundsson <>
Fri Oct 11 08:12:39 CEST 2002


I havn't tested, why don't you do it and tell me :-) 

The problem is the startup where 100 nodes are trying to talk to each
other, discussing what nodes should load which table from disc and
which table should be from loaded from which node and so on...  

The number of messages between nodes during startup is something that
I have to try to reduce sometime, it's currently working by method
'better to be safe than sorry'.

You may also find some bottlenecks in code, i.e. naive operations,
keysearching through tagged tuples may not be the best when all lists
become 100 elements, instead 3 elements.

Once every node have started and loaded all tables, there should not
be any overhead on standard transactions, i.e. the overhead depends on
the number of nodes which has a local copy of the table.

The problem will be schema_transactions, (create_table,
add_table_copy, del_table_copy..) which takes lock on 
the schema which exists on 100 nodes. 
I think I can't do much about the schema_transactions.

/Dan

Hal Snyder writes:
 > We have been arguing amongst ourselves as to the advisability of
 > creating a cluster of between 20 and 100 OTP nodes, all running
 > mnesia, all with the same erlang and mnesia cookies. Individual tables
 > would be replicated sparsely, only where needed.
 > 
 > What is the overhead of a full mesh of n mnesia nodes, not counting
 > replicated transactions? At what point does it become prohibitive?
 > 
 > 
 > P.S.: I was just at the Erlang workshop at PLI2002, but foolishly
 > forgot to ask the above question of the experts. The workshop
 > was quite informative, and more fun than a barrel of monkeys.



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