[Qgis-developer] QEP/RFC sqlite virtual tables

[Matthias Kuhn]

On 28.10.2014 16:30, Hugo Mercier wrote:
> Le 28/10/2014 13:21, Matthias Kuhn a écrit :
>> Hi Hugo
>>
>>> The optimization plan could be: don't try to optimize in the general
>>> case (premature optimization ...), only optimize specific
>>> well-identified cases.
>>> For now the only simple case I can see is when a join is done on tables
>>> from the same database (and the user don't know or can't do a join on
>>> the remote database
>> ... or a developer wants to develop a provider-independent plugin/core
>> functionality that has a good cross-table performance.
> Do you have something in mind ?

Spontaneously: Creating reports based on aggregated statistics, but the
field is widely open.

> Indeed, I don't know well the sqlite dev community.
> I will try to know a bit more about exposure of internal SQLite data
> structures.
> In the worst case we could decide to fork or include parts of the code
> the license is very permissive.
>
> Btw, there is a spatialite / sqlite source distribution in
> src/spatialite (probably only used when WITH_INTERNAL_SPATIALITE is enabled)

I think in src/core/spatialite there is only the spatialite and not the
sqlite sourcecode. I normally don't compile with internal spatialite
(it's an old version? and I like to stay close to upstream and avoid
duplicated libs). It also opens the problem of name collisions for
linking/hard to handle interdependencies between external and internal
sqlite versions and will require us to manually keep the code in sync
when new versions are released.
It would probably be hard (but surely not impossible) and it will
probably need ongoing effort.
Therefore it would be very welcome if the sqlite community is open to
changes.
> Ok, but this performance issue is not related to the backend choice
> (SQLite or our own), right ?

The performance issue itself not. The possible optimization we are
discussing now, yes :-)

Matthias

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