PG Bug reporting form <noreply@postgresql.org> writes:
> The extended query protocol is most often used with the 4 messages in the
> sequence: Parse, Bind, Execute, Sync. Parse, Bind, and Execute all call
> start_xact_command, which will change blockState to TBLOCK_STARTED. However
> it is within the protocol spec to instead do: Parse, Bind, Execute, Parse,
> Bind, Execute, Sync. That is: issue two query executions and then a Sync.
> The Npgsql driver does exactly this at its startup.
> The doc comment for TBLOCK_STARTED says "running single-query transaction",
> but this is a case where a driver can escape that restriction which is
> assumed by the rest of the code. For example, there are various things
> differentiate between STARTED and INPROGRESS or IMPLICIT_INPROGRESS:
> PreventInTransactionBlock, IsInTransactionBlock. Some statements (VACUUM,
> DISCARD ALL) use those functions to prevent their execution in a multi
> statement context, but those can be escaped using the extended protocol.
Hmmm ... I think this is a duplicate of a bug that we just fixed last
week. Please see
https://www.postgresql.org/message-id/flat/17434-d9f7a064ce2a88a3%40postgresql.org
https://git.postgresql.org/gitweb/?p=postgresql.git&a=commitdiff&h=f92944137
and let us know (preferably on that thread) if you think there's
still more to do.
regards, tom lane