On the other hand, usage of some well-defined statement name to trigger the special case would be fine: all pgbouncer versions would pass those parse/bind/exec message as if it were regular messages.
Can you elaborate on what that means exactly? Are you proposing to somehow piggyback on an existing message (e.g. Parse) but use some special statement name that would make PostgreSQL interpret it as a different message type?
Exactly.
For instance: if client sends Parse(statementName=I_swear_the_statement_will_be_used_only_once), then the subsequent message must be BindMessage, and the subsequent must be ExecMessage for exactly the same statement id.
Ah, I understand the proposal better now - you're not proposing encoding a new message type in an old one, but rather a magic statement name in Parse which triggers an optimized processing path in PostgreSQL, that wouldn't go through the query cache etc.
If so, isn't that what the empty statement is already supposed to do? I know there's already some optimizations in place around the scenario of empty statement name (and empty portal).
Also, part of the point here is to reduce the number of protocol messages needed in order to send a parameterized query - not to have to do Parse/Describe/Bind/Execute/Sync - since part of the slowdown comes from that (although I'm not sure how much). Your proposal keeps the 5 messages.
Again, if it's possible to make "Parse/Describe/Bind/Execute/Sync" perform close to Query, e.g. when specifying empty statement/portal, that's obviously the best thing here. But people seem to be suggesting that a significant part of the overhead comes from the fact that there are 5 messages, meaning there's no way to optimize this without a new message type.
Note: it is quite easy to invent a name that is not yet used in the wild, so it is safe.
That's problematic, how do you know what's being used in the wild and what isn't? The protocol has a specification, it's very problematic to get up one day and to change it retroactively. But again, the empty statement seems to already be there for that.
