problem when using osmosis –read-apidb to export database

Hello all

I am trying to export part of database by using osmosis.

My commands:

osmosis --read-apidb host="xxxx" database="xxxx" user="xxxx" password="xxxx" validateSchemaVersion=no --way-key-value keyValueList="railway.tram" --usednode --write-xml file="test.osm"

osmosis --read-apidb host="xxxx" database="xxxx" user="xxxx" password="xxxx" validateSchemaVersion=no --tf accpet-ways highway=motorway --usednode --write-xml file="test.osm"

both commands export complete data of database! I tried --bounding-box option, doesn't work either. Full database has been exported.

Is there anything wrong with my commands?

I am using version 0.43.1 on Ubuntu 12.04

UPDATE: I just realize that it didn't export the whole database, but the exported OSM file is unreasonably huge(1.4GB). I imported an 4.xGB OSM file into database before exporting.