On Wed, Mar 4, 2015 at 8:02 AM, Even Rouault <even.roua...@spatialys.com> wrote:
> Norman, > > > > > the aim is to sync data between masters as per - > > http://dataprotocols.org/couchdb-replication/ An example would be using > > GDAL in QGIS and going offline to edit data and then coming back online, > > the user would need to synchronize the dataset. As replication is a core > > part of CouchDB I would like to add it to the CouchDB OGR Driver. > > If I understand well, you would consider the local copy as a "master", > even if > it is implemented as a non-couchdb instance ? > > How would a user would decide that it enters offline mode : with a special > connection string provided to the CouchDB driver ? > It wouldn't matter, it would only sync with an upstream server if there is an available connection. However it could be useful to override this (3G vs WiFi for example) so I will support a connection string. > > > > > Synchronizing at the database opening is a great idea, that makes sense. > > I've the vague feeling that offline editing and resync with server could be > usefull for other drivers, but I'm not sure if it something that can be > easily > abstracted off the driver (i.e. if they aren't too many driver specific > constraints to take into account during offline editing) > I think it would be useful for other drivers e.g. GeoPackage, however I will put it in CouchDB with minimal API changes (if any) and we can abstract it out later. > > > > > LevelDB would be a new GDAL dependency for the CouchDB driver, the > GeoJSON > > will be persisted in leveldb so that subsequent connections to a couchdb > > database would only retrieve any changes to an upstream CouchDB server. > > LevelDB is under the BSD license. LevelDB is used in PouchDB so it is > > relatively easy to follow that code. I would aim to abstract leveldb > behind > > a OGRCouchDBCache class so that this storage engine could be changed. > > It looks like offline editing would be almost like a driver, no ? You need > to > create/edit/delete features. Create/delete layers? > > As far as LevelDB, my remark would be that it will just make packagers' > life a > bit harder. Would that be a requirement for the CouchDB driver, or would > that > condition the offline editing feature only ? > Are there killer features that you need that couldn't be provided with > SQLite3, which is used for long by GDAL and a dependency satisfied into all > builds I'm aware of ? > I will try with sqlite3, leveldb is a little easier, but I agree with your build concerns. > > Even > > > > > Norman > > > > > > > > On Wed, Mar 4, 2015 at 1:43 AM, Even Rouault <even.roua...@spatialys.com > > > > > > wrote: > > > Norman, > > > > > > I'm not familiar with what this "sync" is about, so please bear with > the > > > naive > > > questions. > > > Is it to synchronize all masters between them ? > > > Why GetFeature() and/or not at the first GetNextFeature(), or at > database > > > opening ? > > > What is the persistence you mention, and what is the connexion with the > > > sync > > > you mention ? Is it done at client (OGR) side ? Would leveldb be a new > > > GDAL dependency ? > > > > > > Even > > > > > > > Hi, > > > > > > > > I am looking to add sync to the GDAL CouchDB driver. I would rather > not > > > > > > add > > > > > > > additional API functions to do this but to wrap it up in the > > > > usual GetFeature call. The first call to GetFeature would initiate a > > > > > > sync, > > > > > > > but thoughts on this are appreciated. > > > > > > > > Sync is a useful function that is a key differentiator with CouchDB > > > > which is a multi-master database. > > > > > > > > There are a couple of ways of doing the sync, I could force a whole > > > > database sync (the CouchDB model) or we could do a filtered sync > based > > > > on the bbox of the current local dataset. I would do the former in > the > > > > > > initial > > > > > > > implementation. > > > > > > > > As for the persistence, I would like to use leveldb as a local store > > > > > > though > > > > > > > I could use sqlite. The two schemas are as follows; > > > > > > > https://github.com/pouchdb/pouchdb/blob/master/lib/adapters/idb/idb.js#L5 > > > 6 > > > > > > > https://github.com/couchbaselabs/TouchDB-iOS/wiki/Object-Design-And-Schem > > > a > > > > > > > I will be create a PR on this shortly, but I am interested in any > early > > > > feedback. > > > > > > > > Norman > > > > > > -- > > > Spatialys - Geospatial professional services > > > http://www.spatialys.com > > -- > Spatialys - Geospatial professional services > http://www.spatialys.com >
_______________________________________________ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev
