Changes between Initial Version and Version 1 of SQLiteStorageDescriptionEN

Timestamp:

Jul 27, 2011, 7:24:04 PM (13 years ago)

Author:

Martin Kolman

Comment:

--

SQLiteStorageDescriptionEN

@@ +1 @@
+== sqlite tile storage == #sqlite
+''available since '''V0.16-1'''''
+
+'''What is this good for ?'''[[br]]
+As mentioned earlier in the modRana thread on talk.maemo.org and also in a related Mappero thread, tiles take up more space than expected because each tile, even if only 500B in size, takes a whole 64kB cluster.
+When using sqlite for tile storage, there are basically just 2 files per layer, not the usual tens of thousands of files and folders.
+
+'''How to enable sqlite tile storage ?'''[[br]]
+Go to '''options'''->'''map''' and switch '''tile storage''' from '''files''' to '''sqlite'''.
+
+'''Is it stable ?'''[[br]]
+It seems to work OK for both normal automatic tile download (including overlay) and batch download. But some errors can still can show up, so please report any unusual behavior, thanks ! :)
+
+'''What about the 4GB maximum file size limit on FAT32 ?'''[[br]]
+When a size of the storage database reaches 3.7 GB, a new one is added. The is no limit on the number of storage databases.
+
+'''How does it work ?'''[[br]]
+The tiles are stored in a sqlite database as blobs. There are two types of database files, ''lookup.sqlite'' and ''store.sqlite''. The lookup file stores a database that indicates in which store the requested tile is. The store file has the actual data. Multiple stores should be numbered in ascending order, starting from 0:
+{{{
+store.sqlite.0
+store.sqlite.1
+store.sqlite.2
+etc.
+}}}
+
+The storage database looks like this:[[br]][[br]]
+{{{table tiles (z integer, x integer, y integer, store_filename string, extension varchar(10), unix_epoch_timestamp integer, primary key (z, x, y, extension))}}}[[br]][[br]][[br]]
+The store databases look like this:[[br]][[br]]
+{{{table tiles (z integer, x integer, y integer, tile blob, extension varchar(10), unix_epoch_timestamp integer, primary key (z, x, y, extension))}}}[[br]][[br]]
+The only difference in the structure is that the lookup databases only stores the name of the store for given coordinates and the store database stores the actual blob.
+Both also have a table called version which has an integer column called v.  There is a single 1 inserted, which indicates the current version of the table.
+
+Database files are stored in the corresponding layer folders.
+
+When looking for a tile in the database, modRana first asks the lookup database and when it gets an answer, it asks the store described in the store_filename for the given tile coordinates.
+
+'''Could this be used by other navigation apps ?'''[[br]]
+Why do you think I just described how it works ? :D