SGA_MAX_SIZE and SGA_TARGET We recently increased sga_max_size from 2g to 4g but didn't increase sga_target. Is it OK not to increase sga_target? The reason we wanted to increase sga is to reduce wait time on sequential reads in our db. Should we increase sga_target too? 

Below is what we currently have.

NAME           TYPE       VALUE          DISPLAY_VALUE
sga_max_size    6         4194304000     4000M
sga_target      6         1996488704     1904M
It is perfectly valid to increase the SGA_MAX_SIZE without changing the SGA_TARGET though it probably isn't going to change your performance.  Setting the SGA_MAX_SIZE to a larger value allows you to adjust the SGA_TARGET upward without restarting the database.  It won't affect the actual amount of RAM allocated to the SGA, that's controlled by the SGA_TARGET.  If your intention was to increase the size of the SGA from 2 GB to 4 GB, you need to adjust the SGA_TARGET.