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Previously we required every exported transaction to have an xid assigned. That was used to check that the exporting transaction is still running, which in turn is needed to guarantee that that necessary rows haven't been removed in between exporting and importing the snapshot. The exported xid caused unnecessary problems with logical decoding, because slot creation has to wait for all concurrent xid to finish, which in turn serializes concurrent slot creation. It also prohibited snapshots to be exported on hot-standby replicas. Instead export the virtual transactionid, which avoids the unnecessary serialization and the inability to export snapshots on standbys. This changes the file name of the exported snapshot, but since we never documented what that one means, that seems ok. Author: Petr Jelinek, slightly editorialized by me Reviewed-By: Andres Freund Discussion: https://postgr.es/m/f598b4b8-8cd7-0d54-0939-adda763d8c34@2ndquadrant.com
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/.