Trying to make sense of multi-farm databases

Stefan Manegold Stefan.Manegold at
Fri Jul 21 13:43:04 CEST 2017

>From `man mserver5` resp. :
Path where mserver5 should find a database. Shorthand for option gdk_dbpath. Default value: /var/monetdb5/dbfarm/demo.

Path where mserver5 should store transient data. Default value is the value of the −−dbpath option.

In other word, one can use the "dbextra" farm to "store" transient data (once they (need to) get
spilled out of memory because their aggregated size exceed physical memory)
in a different location/folder/partition/device than the persistent data (in "dbpath").
E.g. a potential scenario is to have the "dbpath" on a (large) HDD (-RAID),
and the "dbextra" on a (usually smaller but faster) SSD (or NVMe) (-RAID) ...


----- On Jul 21, 2017, at 12:58 PM, Eyal Rozenberg E.Rozenberg at wrote:

> To clarify/correct: I mean this changeset
> (so not sure it was merged in the Jul 2016 release.)
> Also, I remember BATs could  be persistent or transient, but I'm not
> sure that's exactly what this new role field is supposed to mean.
> On 7/21/17 12:05 PM, Eyal Rozenberg wrote:
>> Hello all,
>> I've noticed a change introduced to the release version in Jun 2016 that
>> I can't find a bugzilla bug or a detailed comment for, and I wish to
>> understand a little better: multi-farm DBs, or multi-farm BAT buffer
>> pools if you will.
>> Questions:
>> * Why do we have them?
>> * Are BAT "roles", introduced with the patch for this issue, inherently
>> relevant only with multiple DB farms? If not, why were they introduced
>> at the same time and with the same changeset?
>> * Is this considered a "good idea" design-wise, or perhaps an
>> unfortunate necessity (e.g. due to client needs)?
>> * When you create a new DB, is there a chance more than a single DB farm
>> will be created when you haven't specifically requested this happen?
>> Eyal
>> _______________________________________________
>> developers-list mailing list
>> developers-list at
> _______________________________________________
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