[mapserver-users] Mapcache: error with Berkeley DB and display tiles

[samuelmesa at gmail.com]

 Andreas, thanks for the explanation about the Berkeley Database. However, I
have made several changes of permissions and owner of the files produced by
mapcache_seed, and I still get the same error on the OpenLayers demo.

 I don't know if others users have had the same error with Mapcache and
Berkeley Databases in Ubuntu Server.

 Thanks again,

 Samuel.


2014/1/23 Eichner, Andreas - SID-NLKM <Andreas.Eichner at sid.sachsen.de>

> > Thanks Andreas for your response. I changed all the permissions to
> > read, write and the owner, after restarting apache, it fails
> > displaying tiles in the demo and report the same error:
> >
> > "failed to aquire connection to bdb backend: unknown error"
> >
> > I followed the instructions to check the database created with db_sql
> > according to [1] but I get the same error:
> >
> > > db5.1_sql ortofoto.db
> >
> > "ortoforo.db: multiple databases specified but not supported by file"
> > "Error: file is encrypted or is not a database"
> >
> > I have little knowledge of this type of database, but I would to
> > evaluate the loading speed of tiles.
>
> It seems there is a misunderstanding of the usage of Berkley DB. BDB is a
> library implementing a key/value store and is quite flexible in what can be
> used as key and value.
> And that's the way MapCache uses it. The key is a string representing
> tileset, zoomlevel and any used dimension but at least (x, y) and the value
> is the image BLOB. So there will be a single BDB cache stored in a
> directory (because BDB uses multiple files) for all tilesets configured to
> use this cache.
> The error message you got is a mixed result of BDB (1st: "multiple ...")
> and SQLite (2nd: "file is encrypted..."). This is a new feature since
> Oracle Berkeley DB 11g. It combines the flexibility of the SQLite database
> engine with the strengths of the BDB used as storage backend. See [1] for
> more info on that.
> Although both use-cases use BDB as backend they are in fact completely
> different and cannot be mixed together. So you cannot use dbsql to inspect
> the tilecache. You have to use mapcache_seed to manipulate it (seed/reseed,
> clean).
>
> HTH
>
> [1]
> http://www.oracle.com/technetwork/database/berkeleydb/overview/sql-160887.html
>



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