[Monetdb-developers] Monetdb-developers Digest, Vol 30, Issue 10

Stefan de Konink stefan at konink.de
Sun Nov 23 18:20:16 CET 2008

Peter Boncz wrote:
> With hindsight, this API decision was bad judgement; because the question
> whether real file mapping is used now depends on the question whether the
> filename was initialized at BAT or Hash table creation. Now, this should be
> the case, but it would be my first question to address in a debugging
> session.

If someone wants to try, and has time, I can compile it with debugging 
on again.

> I also recall that in case of the Skyserver TB dataset, key checking was
> disabled to to similar problems.

Foreign key checking doesn't seem to be the problem on the smaller 7GB 
tables for now.

> Of course, if we would find and fix this bug, life will not be rosy for you,
> doing random access (key uniqueness checking) into a 14GB heap that will
> never fit your 2GB RAM. That goes back to your question whether it is in
> fact reasonable to materialize 14GB.

I presume the amount of strings that are effectively stored for each 
string hash table; the amount of users of OSM, the variance in keys used 
< 100. And a big table that shouldn't have many duplicates and is not 
often used as lookup anyway.

> PS
> The likely cause for the problem is a shortage of swap space. Increasing
> your swap file size (with a few 10s of GB) should be a workaround for the
> problem.

I'll give it a shot. Linux seems to like files as swap too. So that 
shouldn't be a problem :)


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