Why a remote query (through Oracle net) can block a rollback segment on the remote database ?

 Hello,

I wonder why a remote query (through Oracle net) can block a rollback segment on the remote database. Indeed, a rollback segment is used when a transaction perform some data uptades, to save the old values (before update). But a remote query doesn't change any data, so why using a rollback segment ?

Thanks for your help,

G. Delferrière