Oracle SGA like feature???

At the company I work at we have undergone a fairly large consolidation
plan.  Due to Oracle's new licensing schemes, we have opted for a model
with many Oracle instances on shared hardware (IBM RS6000 AIX) where we
pay a per CPU license.

In this model, it sounds like we are allocating memory to each Oracle
instance by setting the System Global Area (SGA) for each instance to a
fixed value.  I'm no Oracle DBA, so I don't know all the details, but
this essentially limits the amount of memory that each instance can
consume.

My question then is, does postgreSQL have any similar features that
would allow hosting multiple instances running on the same hardware
within fixed memory allocations???

I am just curious if PostgreSQL may be able to replace some of our
smaller Oracle instances in this environment with an eye to expansion
to the larger instances in the future.

Thanks,

Keehan

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