After RAM upgrade on 32-bit Oracle server, ORA-04031: unable to allocate x bytes of shared memory We are in the process of upgrading our Oracle database server at work, from SUSE Linux Enterprise Server 10.4 / Oracle 10g / 4GB RAM (Intel 32-bit) to Scientific Linux 6.4 / Oracle 12c / 8GB RAM (Intel 64-bit).

As the first step, the additional RAM has been installed, but due to some application-related issue we had to pend the rest of the planned upgrade. To clarify, the server is still running Oracle 10g and SLES 10.4. No change has been made on the software side

Since the installation of the additional RAM, however, the only database instance on that machine has been running out of shared memory (with the error in the title) two afternoons in a row. The depletion was severe enough that the only way to recover was using SHUTDOWN ABORT.

No configuration change has been made, e.g. to the memory settings of the database:

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
lock_sga                             boolean     FALSE
pre_page_sga                         boolean     FALSE
sga_max_size                         big integer 1632M
sga_target                           big integer 1632M
pga_aggregate_target                 big integer 384M
db_16k_cache_size                    big integer 0
db_2k_cache_size                     big integer 0
db_32k_cache_size                    big integer 0
db_4k_cache_size                     big integer 0
db_8k_cache_size                     big integer 0
db_cache_advice                      string      ON
db_cache_size                        big integer 960M


It seems that the extra RAM actually cause the Oracle database software to have less RAM available to itself than before, but how exactly is this happening?
The error just means that the shared_pool ran out of free space. This can be caused by many things, mostly application related. Make sure your shared_pool has a minimum size needed to run your application.
Sometimes it helps to increase the shared_pool_reserved_size so larger objects can be loaded in there.