mbtiles

go-mbtiles

Package mbtiles reads and writes files in the MBTiles format.

Running the http server

go install github.com/twpayne/go-mbtiles/cmd/mbtiles-server
go run github.com/twpayne/go-mbtiles/cmd/mbtiles-server -addr localhost:9091 -dsn ./testdata/openstreetmap.org.mbtiles

Reading mbtiles files

MBTiles files are SQLite databases, and opened using a DSN string.

Create a reader and read a tile with:

reader, err := mbtiles.NewReader("./testdata/openstreetmap.org.mbtiles")
if err != nil {
	panic(err)
}
tile, err := reader.SelectTile(0, 0, 0)
if err != nil {
	if errors.Is(err, sql.ErrNoRows) {
		fmt.Printf("tile doesn't exist: %d, %d, %d\n", 0, 0, 0)
		return
	} else {
		panic(err)
	}
}
fmt.Printf("tile data: %+v\n", tile)

Note that SQLite will happily open a non-existant file to read without throwing an error. It is recommend that you check for existance of the file first, if you're using a file path as your DSN. For example:

if _, err := os.Stat(filename); errors.Is(err, os.ErrNotExist) {
	panic(fmt.Sprintf("mbtiles file doesn't exist (%s): %v", filename, err))
}

The Reader type includes a ServeHTTP function. You can use it to create a reader for your mbtiles.

Writing mbtiles files

This package supports writing files in the MBTiles v1.3 format.

The library will not fill out all the required fields in the MBTiles specification, instead it provides the tools to be compliant.

Of note:

• The caller is responsible for populating the correct metadata into the metadata persuant to the spec.
• The caller is responsible for gzip'ing the tile data before calling InsertTile or BulkInsertTile. The spec requires tiles to be compressed with gzip. How the caller implements the compression is outside the scope of this package.
• For the json key in the metadata table, helper types are provided in this package as mbtiles.MetadataJson. This type can be marshaled to a string and inserted into the metadata table for spec compliance for vector MBTiles files.
• go-mbtiles will invert the Y coordinate to TMS to be compliant with the mbtiles spec.
• go-mbtiles will create a metadata table if it doesn't exist, the first time InsertMetadata is called.
• go-mbtiles will create a tiles table if it doesn't exist, the first time InsertTile or BulkInsertTile is called.

Performance Tips

MBTiles files are SQLite databases. To performantly bulk insert a large number of rows into the database, certain optimizations may be necessary to improve write performance.

SQLite is a a single writer database, which means only one write can occur at a time. The database will otherwise be locked. Because of this, any write that is not in a transaction will automatically be wrapped in a transaction, which is slow. Consider the BulkInsertTile command, which will wrap all of the inserts in a single transaction.

There are other optimizations exposed through the Writer interface. You should understand their implications for your use case before turning them on.

• JournalModeMemory switches journaling from disk to memory. In bulk import scenarios, this is likely a very safe performance optimization to turn on.
• SynchronousOff allows SQLite to continue processing as soon as data is handed off to the operating system to be written (instead of wait for confirmation that the write was successful). This is likely safe for bulk writes, but likely will result in a corrupted database if the process is interrupted or computer loses power.

The performance improvements in go-mbtiles are motivated by the research in this StackOverflow post about SQLite INSERT performance.

License

BSD-2-Clause in LICENCE.

Contributors

• Tom Payne (@twpayne)
• Joe Polastre (@polastre), FlightAware