[GRASS-dev] single vs. multiple sqlite db files [was v.db.calc]
mlennert at club.worldonline.be
Wed May 13 03:25:57 EDT 2009
On 11/05/09 22:59, Dylan Beaudette wrote:
> On Monday 11 May 2009, C Michael Barton wrote:
>> You can have multiple tables in an SQLite database. These are simply
>> imported or created. So joins would be possible between any table in the
>> database. The question is whether to have one SQLite database (with one or
>> more tables, depending on one's need) for each vector file OR to have a
>> single SQLite for ALL vector files in a mapset.
>> The latter has the greatest possibility of making any kind of join between
>> any table used with any vector file in a mapset. However, it breaks the
>> portability we now have with respect to vectors in which you can grab the
>> vector folder from the mapset and copy/move/send it to any other equivalent
>> location with all parts intact (vector GIS files, indexes, and attribute
>> So the issue is whether the ability to make any kind of join between any
>> table within a mapset (does not apply to between mapset joins as proposed
>> currently) is more important than maintaining easy vector portability OR is
>> portability more important than making joins between the tables of
>> different vectors within a mapset?
I would plead for solid modules allowing to export and import GRASS data
between GRASS installations (e.g. something like the r.pack/r.unpack
modules). IMHO, moving around data should not depend on the location of
the database or the choice of database backend (i.e. how do you handle
above export with a PostgreSQL backend ?). We need to povide a mecanism
which allows users to do that while respecting the unwritten law that
they should not have to do anything at all inside their GISDBASE.
> Sure. As long as there is a documented approach to adjusting this behavior. I
> think that apart from joins, the table / file locking issue may be more
> important... If a long-running process is causing the mapset-wide SQLite db
> to be locked, then vector-specific database files would make more sense.
I agree that locking can be a serious issue for sqlite. I didn't think
of this before, but AFAIK, sqlite can only provide file-based locking as
it is a single-file database . With this in mind, I might actually
change my mind and plead for one db per vector, although I agree with
Dylan that sharing data across vector file attributs tables happens
regularly for me.
I guess that sqlite is still more in the same line of solutions as dbf,
only that if provides a much larger set of possibilities, but that if
you want to do any serious use of db functionalities you will in any
case have to turn to PostgreSQL of MySQL...
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