Re: extended query protcol violation?

> Tatsuo Ishii <ishii@sraoss.co.jp> writes:
>> While looking into an issue of Pgpool-II, I found an interesting
>> behavior of a PostgreSQL client.
>> Below is a trace from pgproto to reproduce the client's behavior.
> 
>> It starts a transacton.
> 
>> FE=> Parse(stmt="S1", query="BEGIN")
>> FE=> Bind(stmt="S1", portal="")
>> FE=> Execute(portal="")
>> :
>> Commit the transaction
> 
>> FE=> Parse(stmt="S1", query="COMMIT")
>> FE=> Bind(stmt="S1", portal="")
>> FE=> Execute(portal="")
> 
> Hm, I'd expect the second Parse to generate a "prepared statement already
> exists" error due to reuse of the "S1" statement name.  Is there more
> in this trace than you're showing us?

Oh, yes. Actually the S1 statement was closed before the parse
message. I should have mentioned it in the previous email.

>> Send sync message.
> 
>> FE=> Sync
> 
>> Now the interesting part. After sync it a close message is sent.
> 
>> FE=> Close(stmt="S1")
> 
> That part seems fine to me.
> 
>> I thought all extended query protocol messages are finished by a sync
>> message. But in the example above, a close message is issued, followed
>> by a simple query without a sync message. Should PostgreSQL regard
>> this as a protocol violation?
> 
> No, although it looks like buggy behavior on the client's part, because
> it's unlikely to work well if there's any error in the Close operation.
> The protocol definition is that an error causes the backend to discard
> messages until Sync, so that if that Close fails, the following simple
> Query will just be ignored.  Most likely, that's not the behavior the
> client wanted ... but it's not a protocol violation, IMO.

Yes, you are right. I actually tried with errornouse close message
(instead of giving 'S' to indicate that I want to close a statement, I
gave 'T'). Ssubsequent simple query "BEGIN" was ignored.

BTW, I also noticed that after the last "BEGIN" simple query, backend
responded with CloseComplete message before a CommandComplete message.
Accoring to our docs:

https://www.postgresql.org/docs/11/protocol-flow.html#id-1.10.5.7.4

responses of a simple query do not include CloseComplete (or any other
extended protocol message responses). So it seems current behavior of
the backend does not follow the protocol defined in the doc.  Probably
we should either fix the doc (stats that resoponses from a simple
query are not limited to those messages) or fix the behavior of the
backend.

Here is the whole message exchanging log:

FE=> Parse(stmt="S1", query="BEGIN")
FE=> Bind(stmt="S1", portal="")
FE=> Execute(portal="")
FE=> Close(stmt="S1")
FE=> Parse(stmt="S2", query="SELECT 1")
FE=> Bind(stmt="S2", portal="")
FE=> Execute(portal="")
FE=> Parse(stmt="S1", query="COMMIT")
FE=> Bind(stmt="S1", portal="")
FE=> Execute(portal="")
FE=> Sync
<= BE ParseComplete
<= BE BindComplete
<= BE CommandComplete(BEGIN)
<= BE CloseComplete
<= BE ParseComplete
<= BE BindComplete
<= BE DataRow
<= BE CommandComplete(SELECT 1)
<= BE ParseComplete
<= BE BindComplete
<= BE CommandComplete(COMMIT)
<= BE ReadyForQuery(I)
FE=> Close(stmt="S2")
FE=> Close(stmt="S1")
FE=> Query (query="BEGIN")
<= BE CloseComplete
<= BE CloseComplete
<= BE CommandComplete(BEGIN)
<= BE ReadyForQuery(T)
FE=> Terminate

Best regards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
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