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A parallel worker process should not be making any decisions of its own about whether to auto-explain. If the parent session process passed down flags asking for instrumentation data, do that, otherwise not. Trying to enable instrumentation anyway leads to bugs like the "could not find key N in shm TOC" failure reported in bug #15821 from Christian Hofstaedtler. We can implement this cheaply by piggybacking on the existing logic for not doing anything when we've chosen not to sample a statement. While at it, clean up some tin-eared coding related to the sampling feature, including an off-by-one error that meant that asking for 1.0 sampling rate didn't actually result in sampling every statement. Although the specific case reported here only manifested in >= v11, I believe that related misbehaviors can be demonstrated in any version that has parallel query; and the off-by-one error is certainly there back to 9.6 where that feature was added. So back-patch to 9.6. Discussion: https://postgr.es/m/15821-5eb422e980594075@postgresql.org |
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README
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/.