Efficient mapping over indexed records in Mnesia

Tom McNulty <>
Sat Jun 27 01:22:29 CEST 2009


Hi,

I have a problem very similar to the "Raise" example given in the  
Mnesia manual.  I would like to alter records (re-write), which hold a  
specific secondary index.

So far the only ways I can achieve this are:

1) Gather candidates using index_read, and then fold over the list  
applying my changes, and writing them back. The problem is that this  
initial candidate result set could be massive, and I don't want to  
hold it all in memory. As far as I know, there is no 'lazy' way of  
walking over indexes.

2) Fold over the entire table. I haven't read the implementation, but  
I assume this will solve the mem problem above, at the expense of many  
times the number of disk seeks.   In practice I imagine my partitions  
will exceed no more than 20% of the table, making this approach quite  
wasteful.

Is there anything better I can do with Mnesia?

Thanks,

- Tom



More information about the erlang-questions mailing list