added doc about fieldlength and fieldcount

s3/src/main/java/com/yahoo/ycsb/db/S3Client.java

@@ -43,7 +43,12 @@ import com.amazonaws.services.s3.model.S3ObjectSummary;
  * s3.secretKey=secret key S3 aws
  * s3.endPoint=s3.amazonaws.com
  * s3.region=us-east-1
- *
+ * The parameter table is the name of the Bucket where to upload the files. This must be created before to start the benchmark
+ * The size of the file to upload is determined by two parameters:
+ * - fieldcount this is the number of fields of a record in YCSB
+ * - fieldlength this is the size in bytes of a single field in the record
+ * together these two parameters define the size of the file to upload, the size in bytes is given by the fieldlength multiplied by the fieldcount.
+ * The name of the file is determined by the parameter key. This key is automatically generated by YCSB.
  * @author ivanB1975
  */
 public class S3Client extends DB {
@@ -135,7 +140,8 @@ public class S3Client extends DB {
 	* @param key
 	*            The record key of the file to insert.
 	* @param values
-	*            A HashMap of field/value pairs to insert in the file
+	*            A HashMap of field/value pairs to insert in the file. Only the content of the first field is written to a byteArray
+	*            multiplied by the number of field. In this way the size of the file to upload is determined by the fieldlength and fieldcount parameters.
 	* @return Zero on success, a non-zero error code on error. See the
 	*         {@link DB} class's description for a discussion of error codes.
 	*/