Hi, I also made a pull request in GeoServer for a community module that will integrate the MBTiles store: https://github.com/geoserver/geoserver/pull/1634
Regards, Le mercredi 08 juin 2016 à 18:00 +0100, Nuno Oliveira a écrit : > Hello, > > The proposal has been added to GeoWebCAche wiki: > https://github.com/GeoWebCache/geowebcache/wiki/MBTiles-BlobStore > > I just made a pull request for this work: > https://github.com/GeoWebCache/geowebcache/pull/388 > > Regards, > > Nuno Oliveira > > Le jeudi 19 mai 2016 à 11:00 +0100, Nuno Oliveira a écrit : > > Hi all, > > sorry for the cross posting. > > > > We would like to add MBTiles support to GWC. > > Follows a description of the work with the main issues\limitations. > > > > I would like to have community feedback on this, by the way is there a > > better way to propose this work ? > > > > * MBtiles and SQLitle * > > > > MBtiles is a specification that describe how to store tiles in an SQLite > > database, this will allow us to store many tiles in a single > > SQLite > > file avoiding us file systems headaches: > > https://github.com/mapbox/mbtiles-spec/blob/master/1.1/spec.md. > > > > We can rely on GeoTools gt-mbtiles module for reading and writing MBTiles, > > this way most of the work of implementing this blobstore will > > be > > managing SQLite connections and SQLite files. > > > > SQLite files cannot be managed as simple files. When connections to an > > SQLite database are open we should not delete, move or switch the > > associated file. Databases files can be filled with "empty space" after > > deleting an huge amount of data or can become fragmented after > > frequent inserts, updates or delete operations. > > > > SQLite documentation warns us against putting databases files on a shared > > file system if multiple process need access to it (which is > > our > > case). Unless we can rely on a distributed lock mechanism SQLite databases > > files should not be used with shared stores. > > > > * VACUUM and DiskQuota * > > > > To remove the fragmented space (or the empty space), the VACUUM command > > needs to be executed. Although, performing a VACUUM command as a > > few > > drawbacks: > > > > - During a VACUUM twice the size of the original database file is > > required in disk. > > - During the VACUUM operation no access to the database is allowed. > > - The VACUUM operation copies the whole database which can take minutes. > > > > For these reasons the VACUUM command cannot be performed after each > > operation. When possible we will avoid creating fragmented space. > > For > > example, during a truncate operation we may prefer remove a whole SQLilte > > file instead of deleting part of is content. Another > > consequence > > of the fragmented space is that DiskQuota will not be compatible with this > > blobstore. > > > > * MBTiles Granularity * > > > > Reading and writing tiles on an SQLite database will be slower than writing > > on a file system but will allow us to avoid file system > > headaches. In order to limit the amount of contention on each single > > MBTiles file we will allow users to decide the granularity of the > > files > > so that instead of having a single file for each single layer we will allow > > users to have more granularity. > > > > MBTiles force us to have at least a file per layer and format. If we want > > to support more CRSs we will also need a file for each CRSs. > > By > > configuration it will be possible to configure the granularity of the > > database files. By default we will have a granularity per layer, > > crs, > > format and zoom level. As an instance something like this could be offered: > > > > <blobstore> > > <file>/path/to/{grid}/{dim}/{tileset}/{z}/{x}-{y}.sqlite</file> > > <xcount>1000</xcount> > > <ycount>1000</ycount> > > </blobstore> > > > > In this case we should include the {x}, {y} and {z} replacements in the > > template determining the file to use. In the previous example, > > tile > > (z,x,y)=(15,3024,1534) would be stored in a file named > > /path/to/g/mytileset/15/3000-1000.sqlite3 and tile (5,2,8) would be stored > > in a > > file > > named /path/to/g/mytileset/5/0-0.sqlite3. > > > > With more databases files we have more performance but we will have also > > more files to manage on the file system. In addition we can > > couple > > this with the in-memory cache in order to improve tile serving performance. > > > > * Connection Pooling and Performance * > > > > SQLite allow multiple readers but only allow one writer at the time which > > will block the entire database. At most only one connection > > should > > be open to each SQLite database, the total number of open connections is > > limited by the number of open files allowed by the OS (in linux > > this is controlled by the ulimit). A connection pool that will control the > > number of open connections and that will be responsible to > > manage > > the connections will be implemented. > > > > * Replace Operation * > > > > As said before, if the cache is running we cannot simply switch SQLite > > files, we need to make sure that all connections are closed. A > > replace operation will be created for this propose. The replace operation > > will first copy the new file side by side the old one, then > > block > > the requests to the old file, tear down the store, delete the old one, > > rename the new file to current one, reopen the new db file and > > start > > serving requests again. Should be almost instant. A REST entry point for > > this operation will be created (with the possibility to send > > the > > new file with the request). > > > > Regards, > > -- == GeoServer Professional Services from the experts! Visit http://goo.gl/it488V for more information. == Nuno Miguel Carvalho Oliveira @nmcoliveira Software Engineer GeoSolutions S.A.S. Via di Montramito 3/A 55054 Massarosa (LU) Italy phone: +39 0584 962313 fax: +39 0584 1660272 mob: +39 333 8128928 http://www.geo-solutions.it http://twitter.com/geosolutions_it ------------------------------------------------------- AVVERTENZE AI SENSI DEL D.Lgs. 196/2003 Le informazioni contenute in questo messaggio di posta elettronica e/o nel/i file/s allegato/i sono da considerarsi strettamente riservate. Il loro utilizzo è consentito esclusivamente al destinatario del messaggio, per le finalità indicate nel messaggio stesso. Qualora riceviate questo messaggio senza esserne il destinatario, Vi preghiamo cortesemente di darcene notizia via e -mail e di procedere alla distruzione del messaggio stesso, cancellandolo dal Vostro sistema. 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