also set _pending to 0 to prevent calling COMMIT too frequently

lib/mbtiles.js

@@ -410,12 +410,7 @@ MBTiles.prototype.startWriting = function(callback) {
     var mbtiles = this;
     if (!this._isWritable) {
         this._isWritable = 1;
-        this._pending = 0;
+        this._clearCaches();
-        this._tileCache = {};
-        this._gridCache = {};
-        this._keyCache = {};
-        this._dataCache = {};
-        this._mapCache = {};
         this._db.run('PRAGMA synchronous=OFF', callback);
     } else {
         this._isWritable++;
@@ -423,6 +418,15 @@ MBTiles.prototype.startWriting = function(callback) {
     }
 };
 
+MBTiles.prototype._clearCaches = function() {
+    this._pending = 0;
+    this._tileCache = {};
+    this._gridCache = {};
+    this._keyCache = {};
+    this._dataCache = {};
+    this._mapCache = {};
+};
+
 // (private) Commits the cached changes to the database.
 //
 // - @param {Function(err)} callback
@@ -437,7 +441,6 @@ MBTiles.prototype._commit = function(callback) {
             for (var id in mbtiles._tileCache) {
                 images.run(id, mbtiles._tileCache[id]);
             }
-            mbtiles._tileCache = {};
             images.finalize();
         }
 
@@ -448,7 +451,6 @@ MBTiles.prototype._commit = function(callback) {
             for (var id in mbtiles._gridCache) {
                 grids.run(id, mbtiles._gridCache[id]);
             }
-            mbtiles._gridCache = {};
             grids.finalize();
         }
 
@@ -461,7 +463,6 @@ MBTiles.prototype._commit = function(callback) {
                     keys.run(id, key);
                 });
             }
-            mbtiles._keyCache = {};
             keys.finalize();
         }
 
@@ -472,7 +473,6 @@ MBTiles.prototype._commit = function(callback) {
             for (var key in mbtiles._dataCache) {
                 keymap.run(key, JSON.stringify(mbtiles._dataCache[key]));
             }
-            mbtiles._dataCache = {};
             keymap.finalize();
         }
 
@@ -503,12 +503,12 @@ MBTiles.prototype._commit = function(callback) {
                 mapBoth.run(map.z, map.x, map.y, map.tile_id, map.grid_id);
             }
         }
-        mbtiles._mapCache = {};
         mapBoth.finalize();
         mapTile.finalize();
         mapGrid.finalize();
 
         mbtiles._db.run('COMMIT', callback);
+        mbtiles._clearCaches();
     });
 };