Yes, we've discussed adding some kind of optional identity information
to the object, it remains a potential course of action.
On Tue, Apr 1, 2008 at 2:37 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> "Paul Ramsey" <pramsey(at)cleverelephant(dot)ca> writes:
> > The "optimized" form gets cached and retrieved from a memory context.
> > Each time the function is run within a statement it checks the cache,
> > and sees if one of its arguments are the same as the last time around.
> > If so, it uses the prepared version of that argument. If not, it
> > builds a new prepared version and caches that.
> > The key here is being able to check the identify of the arguments...
> > is this argument A the same as the one we processed last time? One way
> > is to do a memcmp. But it seems likely that PgSQL knows exactly
> > whether it is running a nested loop, or a literal, and could tell
> > somehow that argument A is the same with each call.
> Not really. Certainly there's no way that that information would
> propagate into function calls.
> In the special case where your argument is a literal constant, I think
> there is enough information available to detect that that's the case
> (look at get_fn_expr_argtype). But if it's not, there's no very good
> way to know whether it's the same as last time.
> Perhaps it would be worth changing your on-disk storage format to allow
> cheaper checking? For instance include a hash value.
> regards, tom lane
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