this.heapFile = heapFile;
this.keylength = keylength;
this.index = null; // will be created as result of initialization process
this.free = null; // will be initialized later depending on existing idx/gap file
this.heapFile.getParentFile().mkdirs();
this.file = new CachedFileWriter(this.heapFile);
// read or initialize the index
fingerprintFileIdx = null;
fingerprintFileGap = null;
if (initIndexReadDump()) {