NSS Ltd writes:
I've also been looking at other uses of 'any' since I think they may
require changed too for performance (and to be consistent) but Arnt may
be better to say if this is the case. I'm making a patch set with those
changed too.
Postgres has two parsers, one for SQL and one for values. (The second is
mostly used with prepared statements.) When you say
select * from mailbox_messages mm where mm.uid=104
then all of that is handled by the SQL parser. When you say
select * from mailbox_messages mm where mm.uid=any{[104,107]}
then all of that is handled by the SQL parser. When you say
select * from mailbox_messages mm where mm.uid=any{$1}
and
$1=[104,107]
then the SQL parser has to handle 54 bytes and the value parser has to
handle about ten bytes (eight or twelve I think, but I don't remember).
Thus, your patch moves load from the value parser to the SQL parser. The
total load on postgres is the same, but a great big weight is moved from
one subsystem to another.
I am deeply uncomfortable with that move, unless Abhijit says it's OK.
(I am also, separately, uncomfortable with the existence of the load.
That's why I added the two if() clauses, both of which eliminate the load
in fairly common cases.)
Arnt
