How to check my usage (data size) of Oracle XE?

Question

The maximum is 4G, right? How can I know how much there is left, from sqlplus? Thanks so much!
Also, if I use up the space, can I back up my DB and empty it for future use?

Answer 1

Here's a couple dictionary queries to find out the used space and who owns the blocks ...
select a.tablespace_name ts, a.file_id,
sum(b.bytes)/count(*) bytes,
sum(b.bytes)/count(*) - sum(a.bytes) used,
sum(a.bytes) free,
nvl(100-(sum(nvl(a.bytes,0))/(sum(nvl(b.bytes,0))/count(*)))*100,0) pct_used
from sys.dba_free_space a, sys.dba_data_files b
where a.tablespace_name = b.tablespace_name and a.file_id = b.file_id
and a.tablespace_name not in ('SYSTEM', 'SYSAUX','UNDOTBS')
group by a.tablespace_name, a.file_id
order by 1System, sysaux, undo aren't supposed to count toward the 4G. To see the totals by schema ...
select OWNER, TABLESPACE_NAME, sum( BYTES ) from dba_segments
where tablespace_name not in ('SYSTEM', 'SYSAUX','UNDOTBS')
group by OWNER, TABLESPACE_NAME;If you're bumping into the 4G limit and decide one of those OWNERs can be trashed, that will certainly free up space.
drop user [username] cascade;Check the utilities docs on export and datapump, one way to back up a username is to do an OWNER=username dump or just shut down the database and make a backup of the datafiles some place safe-