As per I know when I am fetching the records from salesforce using bulk API , each batch contains 10,000 records.
Currently I have more than 5,00,000 records in my salesforce enterprise org, but it is creating only one batch  and using that batch it is retrieving all the records . What may be the reason? .

I have done the following steps :
1 : Created a job using sessionId
2 : added a batch to the job and got the following output

output :
----------

<?xml version="1.0" encoding="UTF-8"?><batchInfo
   xmlns="http://www.force.com/2009/06/asyncapi/dataload">
<id>75190000001NuAWAA0</id>     -----> Only one batch is created for more than 5,00,000 records
<jobId>75090000000jZVAAA2</jobId>
<state>Queued</state>
<createdDate>2014-03-10T05:35:49.000Z</createdDate>
<systemModstamp>2014-03-10T05:35:49.000Z</systemModstamp>
<numberRecordsProcessed>0</numberRecordsProcessed>
<numberRecordsFailed>0</numberRecordsFailed>
<totalProcessingTime>0</totalProcessingTime>
<apiActiveProcessingTime>0</apiActiveProcessingTime>
<apexProcessingTime>0</apexProcessingTime>
</batchInfo>

3 : Retrieved the batch result using the query : Select Id from Case , It is returning all the 5,00,000 Ids.

Please help me to get to know the things clearly.
Also let me know if is there any way to set the batch size manually.

Thanks
Anupama