[postgis-devel] Re: [HACKERS] Access to Row ID information in Functions

[Paul Ramsey]

Thanks Tom,

Yes, we've discussed adding some kind of optional identity information
to the object, it remains a potential course of action.

Paul

On Tue, Apr 1, 2008 at 2:37 PM, Tom Lane <tgl at sss.pgh.pa.us> wrote:
> "Paul Ramsey" <pramsey at cleverelephant.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
>