Trying to make sense of multi-farm databases

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


>From `man mserver5` resp. https://www.monetdb.org/Documentation/mserver5-man-page :
"
−−dbpath=path
Path where mserver5 should find a database. Shorthand for option gdk_dbpath. Default value: /var/monetdb5/dbfarm/demo.

−−dbextra=path
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) ...

Stefan

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

> To clarify/correct: I mean this changeset
> https://github.com/MonetDB/MonetDB/commit/a251c8a29e23aad62b19ce9550d2f19b94520bc8
> 
> (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 monetdb.org
>> https://www.monetdb.org/mailman/listinfo/developers-list
>> 
> _______________________________________________
> developers-list mailing list
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