Memory related issue

Dear DBA's

Could you please help me on the below scenario.

Let assume In a standalone database, The memory_target and memory_max_target is set to 2G. My understanding is when ever a user is performing a update operation on a table, The blocks which are responsible will be pulled into the memory area and perform the update and will write back to the file system or disk once the user commit. Here in our case, The user is updating a 10G table with no commit until all the 10G table data update to be done. I mean the user is going to commit only after all the 10 GB table data has