Neo4j BatchInserter initializing Db on restart - neo4j

Question

I am using Neo4j BatchInserters to insert nodes in db.I am using LuceneBatchInserterIndexProvider for indexes. I have multiple files from where i am importing the data. I want if my process break then i should be able to restart the process from next file. But whenever i restart process it creates new db in graph folder and new indexes. My initialization code look like this.
Map<String, String> config = new HashMap<String, String>();
config.put("neostore.nodestore.db.mapped_memory", "2G");
config.put("batch_import.keep_db", "true");
BatchInserter db = BatchInserters.inserter("ttl.db", config);
BatchInserterIndexProvider indexProvider = new LuceneBatchInserterIndexProvider(
db);
index = indexProvider.nodeIndex("ttlIndex",
MapUtil.stringMap("type", "exact"));
index.setCacheCapacity(URI_PROPERTY, indexCache + 1);
Can somebody please help here?
To provide more details. I have multiple files ( around 400) which i want to import to Neo4j.
I want to divide my process into batches. After every batch i want to restart the process.
I used neo4j batch inserter config batch_import.keep_db = "true". This does not clear the graph but after restart indexer has lost information. I have this method to check for node existence. I am sure before restart i have created node.
private Long getNode(String nodeUrl)
{
IndexHits<Long> hits = index.get(URI_PROPERTY, nodeUrl);
if (hits.hasNext()) { // node exists
return hits.next();
}
return null;
}