Re: NOT EXIST for PREPARE

On Wed, Mar 23, 2016 at 12:46 PM, Vladimir Sitnikov
<sitnikov(dot)vladimir(at)gmail(dot)com> wrote:
> 2016-03-23 16:21 GMT+03:00 Merlin Moncure <mmoncure(at)gmail(dot)com>:
> Merlin> A typical pattern is for the application to
> Merlin> prepare them all upon startup, but currently each PREPARE needs to be
> Merlin> wrapped with an exception handler in case someone else prepared it
> Merlin> first.
>
> If you plan to have "prepare if not exists" at startup only, why don't
> you just wrap it with
> exception handler then?

That's impolite to our users. Virtually all other commands have been
decorated with IF [NOT] exists to avoid having to guard with exception
handler -- why not this one? Also, if the handler is on the client
side, it tends to be racey.

> If you plan to always issue "prepare if not exists", then you will
> have to send full query text
> for each prepare => overhead. Those repeated query texts are
> "endless copies of the same PREPARE statements" Craig is talking about.

No one is arguing that that you should send it any every time (at
least -- I hope not).

> Merlin>The client prepares the statement exactly
> Merlin>once. The problem is there's no easy way to determine if someone else
> Merlin>prepared it first
>
> Merlin, if by "client" you somehow mean JDBC (e.g. pgjdbc), then it
> does track which connections
> have which queries prepared.

Again, not in pooling scenarios. The problems integrating server side
prepared statements with pgbouncer are well known.

merlin