Re: proposal: psql: show current user in prompt - Mailing list pgsql-hackers
| From | Pavel Stehule |
|---|---|
| Subject | Re: proposal: psql: show current user in prompt |
| Date | |
| Msg-id | CAFj8pRD5wWbEpyO9toNrGebWe1bKgRWHcdCMqY7UvaR=ibKdZQ@mail.gmail.com Whole thread Raw |
| In response to | Re: proposal: psql: show current user in prompt (Jelte Fennema <postgres@jeltef.nl>) |
| Responses |
Re: proposal: psql: show current user in prompt
|
| List | pgsql-hackers |
čt 10. 8. 2023 v 14:05 odesílatel Jelte Fennema <postgres@jeltef.nl> napsal:
On Tue, 8 Aug 2023 at 07:20, Pavel Stehule <pavel.stehule@gmail.com> wrote:
> The reason why I implemented separate flow is usage from psql and independence of transaction state. It is used for the \set command, that is non-transactional, not SQL. If I inject this message to some other flow, I lose this independence.
I still don't understand the issue that you're trying to solve by
introducing a new flow for handling the response. What do you mean
with independence of the transaction state? That it is not rolled-back
in a case like this?
BEGIN;
\set PROMPT '%N'
ROLLBACK;
surely not.
\set is client side setting, and it is not transactional. Attention - "\set" and "set" commands are absolutely different creatures.
That seems more like a Postgres server concern, i.e. don't revert the
change back on ROLLBACK. (I think your current server-side
implementation already does that)
Postgres does it, but not on the client side. What I know, almost all environments don't support transactions on the client side. Postgres is not special in this direction.
I guess one reason that I don't understand what you mean is that libpq
doesn't really care about "transaction state" at all. It's really a
wrapper around a socket with easy functions to send messages in the
postgres protocol over it. So it cares about the "connection state",
but not really about a "transaction state". (it does track the current
connection state, but it doesn't actually use the value except when
reporting the value when PQtransactionStatus is called by the user of
libpq)
> Without independence on transaction state and SQL, I can just implement some SQL function that sets reporting for any GUC, and it is more simple than extending protocol.
I don't understand why this is not possible. As far as I can tell this
should work fine for the usecase of psql. I still prefer the protocol
message approach though, because that makes it possible for connection
poolers to intercept the message and handle it accordingly. And I see
some use cases for this reporting feature for PgBouncer as well.
Maybe we are talking about different features. Now, I have no idea how the proposed feature can be useful for pgbouncer?
Sure If I implement a new flow, then pgbouncer cannot forward. But it is not too hard to implement redirection of new flow to pgbouncer.
However, I think this is probably the key thing that I don't
understand about the problem you're describing: So, could you explain
in some more detail why implementing a SQL function would not work for
psql?
I try to get some consistency. psql setting and some features like formatting doesn't depend on transactional state. It depends just on connection. This is the reason why I don't want to inject dependency on transaction state. Without this dependency, I don't need to check transaction state, and I can execute prompt settings immediately. If I implement this feature as transactional, then I need to wait to idle or to make a new transaction (and this I have not under my control). I try to be consistent with current psql behaviour. It Would be strange (can be very messy) if I had a message like "cannot set a prompt, because you should do ROLLBACK first"
When this feature should be implemented as an injected message, then I have another problem. Which SQL command I have to send to the server, when the user wants to set a prompt? And then I don't need to implement a new message, and I can just implement the SQL function pg_catalog.report_config(...).
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