error log, tablespace, wal files

Hello,

1) what is tablespace in postgres?

2) one more issue is that, I try to rename or delete some file in
/opt/PostgresPlus/9.0/data/base/16428/ directory. when I restart postgres
server, it start normally. but I thing this is wrong. I rename or delete
file into above directory, that means my database(having 16428 oid) is
corrupted. So How can my postgres server is started normally?? I want to
see the log file for that database corruption. Can I see it?? and where???
and please explain me that what's going on in above case??????

3) I want know about pg_xlog(wal) file creation. That means, size of
wal files and how to create that files and time stamp between creation of
two different wal files, that means when one file is created on 11:53AM, so
how much time after the second file is created?? can we set that time
stamp???

Please any one explain me above points.

Regards,
Karuna karpe.