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pgstat_report_wait_start() and pgstat_report_wait_end() required two conditional branches so far. One to check if MyProc is NULL, the other to check if pgstat_track_activities is set. As wait events are used around comparatively lightweight operations, and are inlined (reducing branch predictor effectiveness), that's not great. The dependency on MyProc has a second disadvantage: Low-level subsystems, like storage/file/fd.c, report wait events, but architecturally it is preferable for them to not depend on inter-process subsystems like proc.h (defining PGPROC). After this change including pgstat.h (nor obviously its sub-components like backend_status.h, wait_event.h, ...) does not pull in IPC related headers anymore. These goals, efficiency and abstraction, are achieved by having pgstat_report_wait_start/end() not interact with MyProc, but instead a new my_wait_event_info variable. At backend startup it points to a local variable, removing the need to check for MyProc being NULL. During process initialization my_wait_event_info is redirected to MyProc->wait_event_info. At shutdown this is reversed. Because wait event reporting now does not need to know about where the wait event is stored, it does not need to know about PGPROC anymore. The removal of the branch for checking pgstat_track_activities is simpler: Don't check anymore. The cost due to the branch are often higher than the store - and even if not, pgstat_track_activities is rarely disabled. The main motivator to commit this work now is that removing the (indirect) pgproc.h include from pgstat.h simplifies a patch to move statistics reporting to shared memory (which still has a chance to get into 14). Author: Andres Freund <andres@anarazel.de> Discussion: https://postgr.es/m/20210402194458.2vu324hkk2djq6ce@alap3.anarazel.de |
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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/.