5c1ed0a516
Commit a4ccc1cef introduced the Generation Context and modified the logical decoding process to use a Generation Context with a fixed block size of 8MB for storing tuple data decoded during logical decoding (i.e., rb->tup_context). Several reports have indicated that the logical decoding process can be terminated due to out-of-memory (OOM) situations caused by excessive memory usage in rb->tup_context. This issue can occur when decoding a workload involving several concurrent transactions, including a long-running transaction that modifies tuples. By design, the Generation Context does not free a memory block until all chunks within that block are released. Consequently, if tuples modified by the long-running transaction are stored across multiple memory blocks, these blocks remain allocated until the long-running transaction completes, leading to substantial memory fragmentation. The memory usage during logical decoding, tracked by rb->size, does not account for memory fragmentation, resulting in potentially much higher memory consumption than the value of the logical_decoding_work_mem parameter. Various improvement strategies were discussed in the relevant thread. This change reduces the block size of the Generation Context used in rb->tup_context from 8MB to 8kB. This modification significantly decreases the likelihood of substantial memory fragmentation occurring and is relatively straightforward to backport. Performance testing across multiple platforms has confirmed that this change will not introduce any performance degradation that would impact actual operation. Backport to all supported branches. Reported-by: Alex Richman, Michael Guissine, Avi Weinberg Reviewed-by: Amit Kapila, Fujii Masao, David Rowley Tested-by: Hayato Kuroda, Shlok Kyal Discussion: https://postgr.es/m/CAD21AoBTY1LATZUmvSXEssvq07qDZufV4AF-OHh9VD2pC0VY2A%40mail.gmail.com Backpatch-through: 12
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/.