Is shrink a safe online operation? We are planning to run the following space management command:

alter table XXX shrink space cascade


on a production database (Oracle 10g). The XXX table is a transactional table heavily used  for updates/inserts/deletes by many applications.

I am wondering if running the shrink command during the peak time (online) will cause a severe performance degradation, or may lock the table and so block all the applications?

Can you clarify the impact of the shrink command on the access to the databese table XXX?
As I understand it the resizing of the high water mark requires an exclusive table lock, which in theory might not be a problem as it would be of very short duration. However if it has to wait on other transactions before it gets the lock it will block other transactions.

https://forums.oracle.com/forums/thread.jspa?threadID=2453756

However as the docs point out, you could run a shrink space compact, which does not move the HWM, and run the shrink later on when the system is known to be quiet: http://docs.oracle.com/cd/B28359_01/server.111/b28286/statements_3001.htm#i2192484