Re: forced sequential scan when condition has current_user

On Jan 4, 2010, at 1:59 PM, Robert Haas wrote:

> The thing is, PostgreSQL doesn't know at planning time what the value of
> current_user() will be, so the plan can't depend on that; the planner
> just takes its best shot.

current_user() is a stable function and the manual is explicit that the result of stable function can be used in an
indexscan: 

"A STABLE function cannot modify the database and is guaranteed to return the same results given the same arguments for
allrows within a single statement. This category allows the optimizer to optimize multiple calls of the function to a
singlecall. In particular, it is safe to use an expression containing such a function in an index scan condition.
(Sincean index scan will evaluate the comparison value only once, not once at each row, it is not valid to use a
VOLATILEfunction in an index scan condition.)" 

postgres=# select provolatile from pg_proc where proname = 'current_user';
 provolatile
-------------
 s

So, I think the OP's question is still valid.

Erik Jones, Database Administrator
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