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In batching mode, COPY was using the same (per-tuple) memory context for allocations with longer lifetime. This was confusing but harmless, until commit 31f3817402 added COPY FROM ... WHERE feature, introducing a risk of memory leak. The "per-tuple" memory context was reset only when starting new batch, but as the rows may be filtered out by the WHERE clauses, that may not happen at all. The WHERE clause however has to be evaluated for all rows, before filtering them out. This commit separates the per-tuple and per-batch contexts, removing the ambiguity. Expressions (both defaults and WHERE clause) are evaluated in the per-tuple context, while tuples are formed in the batch context. This allows resetting the contexts at appropriate times. The main complexity is related to partitioning, in which case we need to reset the batch context after forming the tuple (which happens before routing to leaf partition). Instead of switching between two contexts as before, we simply copy the last tuple aside, reset the context and then copy the tuple back. The performance impact is negligible, and juggling with two contexts is not free either. Discussion: https://www.postgresql.org/message-id/flat/CALAY4q_DdpWDuB5-Zyi-oTtO2uSk8pmy+dupiRe3AvAc++1imA@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/.