osmosis osm-> mysql import


every time I import an osm file, I get error messages about duplicate entries in the database.
the id’s causing the error change from file to file.

What could cause such a problem? I always believed that .osm files are more or less dumps of the osm database and as such should not have duplicate data entries.

org.openstreetmap.osmosis.core.OsmosisRuntimeException: Unable to bulk insert node tags into the database.
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Duplicate entry '497160947-1-bus line ' for key 'PRIMARY'
SEVERE: Execution aborted.