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Failing to do so results in an error when a pgbench script tries to start a serializable transaction inside a pipeline, because by the time BEGIN ISOLATION LEVEL SERIALIZABLE is executed, we're already in a transaction that has acquired a snapshot, so the server rightfully complains. We can work around that by preparing all commands in the pipeline before actually starting the pipeline. This changes the existing code in two aspects: first, we now prepare each command individually at the point where that command is about to be executed; previously, we would prepare all commands in a script as soon as the first command of that script would be executed. It's hard to see that this would make much of a difference (particularly since it only affects the first time to execute each script in a client), but I didn't actually try to measure it. Secondly, we no longer use PQsendPrepare() in pipeline mode, but only PQprepare. There's no specific reason for this change other than no longer needing to do differently in pipeline mode. (Previously we had no choice, because in pipeline mode PQprepare could not be used.) Backpatch to 14, where pgbench got support for pipeline mode. Reported-by: Yugo NAGATA <nagata@sraoss.co.jp> Discussion: https://postgr.es/m/20210716153013.fc53b1c780b06fccc07a7f0d@sraoss.co.jp
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/.