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Tom Lane a0c632c1de Force immediate commit after CREATE DATABASE etc in extended protocol.
We have a few commands that "can't run in a transaction block",
meaning that if they complete their processing but then we fail
to COMMIT, we'll be left with inconsistent on-disk state.
However, the existing defenses for this are only watertight for
simple query protocol.  In extended protocol, we didn't commit
until receiving a Sync message.  Since the client is allowed to
issue another command instead of Sync, we're in trouble if that
command fails or is an explicit ROLLBACK.  In any case, sitting
in an inconsistent state while waiting for a client message
that might not come seems pretty risky.

This case wasn't reachable via libpq before we introduced pipeline
mode, but it's always been an intended aspect of extended query
protocol, and likely there are other clients that could reach it
before.

To fix, set a flag in PreventInTransactionBlock that tells
exec_execute_message to force an immediate commit.  This seems
to be the approach that does least damage to existing working
cases while still preventing the undesirable outcomes.

While here, add some documentation to protocol.sgml that explicitly
says how to use pipelining.  That's latent in the existing docs if
you know what to look for, but it's better to spell it out; and it
provides a place to document this new behavior.

Per bug #17434 from Yugo Nagata.  It's been wrong for ages,
so back-patch to all supported branches.

Discussion: https://postgr.es/m/17434-d9f7a064ce2a88a3@postgresql.org
2022-07-26 13:07:03 -04:00
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doc Force immediate commit after CREATE DATABASE etc in extended protocol. 2022-07-26 13:07:03 -04:00
src Force immediate commit after CREATE DATABASE etc in extended protocol. 2022-07-26 13:07:03 -04:00
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PostgreSQL Database Management System
=====================================

This directory contains the source code distribution of the PostgreSQL
database management system.

PostgreSQL is an advanced object-relational database management system
that supports an extended subset of the SQL standard, including
transactions, foreign keys, subqueries, triggers, user-defined types
and functions.  This distribution also contains C language bindings.

PostgreSQL has many language interfaces, many of which are listed here:

	https://www.postgresql.org/download/

See the file INSTALL for instructions on how to build and install
PostgreSQL.  That file also lists supported operating systems and
hardware platforms and contains information regarding any other
software packages that are required to build or run the PostgreSQL
system.  Copyright and license information can be found in the
file COPYRIGHT.  A comprehensive documentation set is included in this
distribution; it can be read as described in the installation
instructions.

The latest version of this software may be obtained at
https://www.postgresql.org/download/.  For more information look at our
web site located at https://www.postgresql.org/.