Mnemosyne Problems?

Hans Nilsson <>
Tue Jan 28 11:27:35 CET 2003


On Thu, 23 Jan 2003, Wiger Ulf wrote:

> (http://www.erlang.se/publications/xjobb/sql_compiler_report.pdf) lists a
> few things that should be fixed in mnemosyne, but also hints that it does a
> pretty good job already. Others who have actually used it more may have more

The focus in the Mnemosyne prototype was on query *optimization*.  In DBMS
query evaluation one have to change evaluation strategy completly
depending on the actual data sets involved in the query.  There are
extreme cases reported in the litterature (with other DBMS) were execution
time could go from 24 hours to 1 minute by just swithcing two subgoals in
a complex query with large and nasty data sets.

If there is a simple query or small and "nice" data sets this effect is
not messurable and the optimization phase is just a timecomsuming null
operation:  the optimizer just suggests to evaluate the query straight on
from the begining to the end.

I agree completly that the kind of data where Mnemosyne's query
otimization present good result is not present in telecom systems.

> 
> For historical reasons, it was never really given a chance to mature from
> prototype to product, but was basically just thrown into the first OTP
> together with mnesia. While mnesia _was_ extremely useful for telecoms and
> was put under high pressure to improve over the years, mnemosyne was not
> given the same attention.

Exactly!!

/Hans




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