Mnesia and the Erlang message distribution model

Dan Gudmundsson dgud@REDACTED
Fri Feb 22 08:27:37 CET 2002


Kurt Luoto writes:
 > I'm a newcomer to Erlang/OTP, and I have a some Mnesia questions.  I'll post
 > each in a separate email so we can maintain separate threads for each.

And I'll answer all of them in the same thread :-) 
Since the short answer to all your questions is .. no.
 > So I would like to know if it is possible to set up a sparse communications
 > topology to match the hardware configuration.  If necessary, I could live
 > with having Mnesia replicate tables such that each control processor has
 > local copies of all the data it needs for its chassis, with the hope that
 > within each chassis the line card's copy of Mnesia only needs to deal with
 > control processor's copy of Mnesia.
 > Is this possible today?
 > -- Kurt Luoto

No you can't create topologies inside mnesia, mnesia requires to be fully
connected to all the nodes in the schema. 

You would have to create separate mnesia schemas/clusters (set of nodes), but
since mnesia doesn't handle several schemas, the set of nodes for each
cluster may not overlap with each other. 
If you want tables to be globally available to all nodes, you would
have to keep them updated manually, i.e. in each cluster have one
process that subscribes to all changes in the table and updates the
other clusters, you will loose the ACID properties though.

Comments about the redundant nodes mail from the database view, this
also breaks mnesia functionality since the mnesia nodes needs to be
fully connected, i.e. you can't have mnesia running on the hot

Sorry for ruin your day :-(

Dan Gudmundsson               Project:    Mnesia, Erlang/OTP
Ericsson Utvecklings AB       Phone:      +46  8 727 5762 
UAB/F/P                       Mobile:     +46 70 519 9469
S-125 25 Stockholm            Visit addr: Armborstv 1 

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