Re: [gnome-db] meta store.

On Fri, 2009-07-17 at 14:08 +0200, Vivien Malerba wrote:

> 
> 
> 
> 2009/7/17 Bas Driessen <[email protected]>
> 
>         Hello,
>         
>         Question regarding meta store. There is a function to update
>         the meta store as follows:
>         
>         gda_connection_update_meta_store
>         
>         When I run this, it waits about 10 seconds or so, so I assume
>         it is building the meta store. However, when it is finished, I
>         don't see any output. I would expect files to show up in
>         etc/libgda-4.0, but nothing is added there. Is there meant to
>         be any output?
>         
>         Also if this generates a structure in memory only, does that
>         mean that I have to call this function every time when I start
>         my application? 
>         
>         My understanding was, that the meta store was written to an
>         XML file and that the libgda would reference that. Only when a
>         table layout has changed, you would run the
>         gda_connection_update_meta_store function to update the XML
>         files.
> 
> Meta data storage has changed since V3. In V3, getting the meta data
> was quicker and created an XML file which was loaded in memory even if
> unused. There were problems with that approach:
> * it used memory even when not required
> * not much meta data was being fetched (which is why it was so fast),
> the main missing feature was that database schemas were not handled.
> * the loading time would have increased and the consummed memory as
> well if I had added the missing meta data
> * it was almost impossible to the API used to add some personnal data
> to the dictionary.
> 
> So in V4:
> * the meta data is now stored in a database instead of an XML file
> * the data is not loaded in main memory if not needed
> * the meta data being fetched now includes schemas, triggers, ...
> * the database used to store meta data from a connection can be
> configured, see
> http://library.gnome.org/devel/libgda/stable/gda-dict.html#GdaMetaStoreSetup. By default a temporary database is created, destroyed when the connection is closed (more exactly when the GdaMetaStore object associated to the connection is destroyed).
> 
> it's up to the user to handle the meta data updates, probably one time
> to get the complete meta data the first time, and then incremental
> updates when database objects are created or removed. This is what
> Libgda's tools (the gda-sql console program and the upcomming
> gda-browser UI program) do: then create an SQLite database to store
> meta data in $HOME/.local/share/libgda
> 
Thanks Vivien. So if I use a postgresql database, will the meta data be
stored in a postgresql table? If so where is it, as I can not see it in
the psql command line tool. 

In order to cache, I need to prevent that this meta data is removed upon
exiting my application, correct? Is that all explained of how to do that
in the link you sent me?  Well, I probably better read it first :)

Bas.

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