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After restart, we don't perform streaming of an in-progress transaction if it was previously decoded and confirmed by the client. To achieve that we were comparing the END location of the WAL record being decoded with the WAL location we have already decoded and confirmed by the client. While decoding the commit record, to decide whether to process and send the complete transaction, we compare its START location with the WAL location we have already decoded and confirmed by the client. Now, if we need to queue some change in the transaction while decoding the commit record (e.g. snapshot), it is possible that we decide to stream the transaction but later commit processing decides to skip it. In such a case, we would needlessly send the changes and later when we decide to skip it, we will send stream abort. We also sometimes decide to stream the changes when we actually just need to process them locally like a change for invalidations. This will lead us to send empty streams. To avoid this, while queuing each change for decoding, we remember whether the transaction has any change that actually needs to be sent downstream and use that information later to decide whether to stream the transaction or not. Note, we can't avoid all cases where we have to send empty streams like the case where the plugin later decides that the change is not publishable. However, we will no longer need to send stream_abort when we skip sending a particular transaction. Author: Dilip Kumar Reviewed-by: Hou Zhijie, Ashutosh Bapat, Shi yu, Amit Kapila Discussion: https://postgr.es/m/CAFiTN-tHK=7LzfrPs8fbT2ksrOJGQbzywcgXst2bM9-rJJAAUg@mail.gmail.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/.