hi Sameer,
1, Yes, you can`t use abap memory.
2, For the shared memory and buffer, you need to take care size of the two memory. Shared buffer will cleared automatically when it reaches the maxinum limit. So for those two, shared buffer is a better option.
Alternatively, you can use 'OPEN DATASET'.
I wanna know how huge data the table have? if really really much, how about delete all data after you extract all data from DB table? then insert it back. i think 'insert' will fast than 'modify'.
Waiting Nabheet give you a help. 
regards,
Archer