Andres Freund da7226993f aio: Add core asynchronous I/O infrastructure The main motivations to use AIO in PostgreSQL are: a) Reduce the time spent waiting for IO by issuing IO sufficiently early. In a few places we have approximated this using posix_fadvise() based prefetching, but that is fairly limited (no completion feedback, double the syscalls, only works with buffered IO, only works on some OSs). b) Allow to use Direct-I/O (DIO). DIO can offload most of the work for IO to hardware and thus increase throughput / decrease CPU utilization, as well as reduce latency. While we have gained the ability to configure DIO in `d4e71df6`, it is not yet usable for real world workloads, as every IO is executed synchronously. For portability, the new AIO infrastructure allows to implement AIO using different methods. The choice of the AIO method is controlled by the new io_method GUC. As of this commit, the only implemented method is "sync", i.e. AIO is not actually executed asynchronously. The "sync" method exists to allow to bypass most of the new code initially. Subsequent commits will introduce additional IO methods, including a cross-platform method implemented using worker processes and a linux specific method using io_uring. To allow different parts of postgres to use AIO, the core AIO infrastructure does not need to know what kind of files it is operating on. The necessary behavioral differences for different files are abstracted as "AIO Targets". One example target would be smgr. For boring portability reasons, all targets currently need to be added to an array in aio_target.c. This commit does not implement any AIO targets, just the infrastructure for them. The smgr target will be added in a later commit. Completion (and other events) of IOs for one type of file (i.e. one AIO target) need to be reacted to differently, based on the IO operation and the callsite. This is made possible by callbacks that can be registered on IOs. E.g. an smgr read into a local buffer does not need to update the corresponding BufferDesc (as there is none), but a read into shared buffers does. This commit does not contain any callbacks, they will be added in subsequent commits. For now the AIO infrastructure only understands READV and WRITEV operations, but it is expected that more operations will be added. E.g. fsync/fdatasync, flush_range and network operations like send/recv. As of this commit, nothing uses the AIO infrastructure. Later commits will add an smgr target, md.c and bufmgr.c callbacks and then finally use AIO for read_stream.c IO, which, in one fell swoop, will convert all read stream users to AIO. The goal is to use AIO in many more places. There are patches to use AIO for checkpointer and bgwriter that are reasonably close to being ready. There also are prototypes to use it for WAL, relation extension, backend writes and many more. Those prototypes were important to ensure the design of the AIO subsystem is not too limiting (e.g. WAL writes need to happen in critical sections, which influenced a lot of the design). A future commit will add an AIO README explaining the AIO architecture and how to use the AIO subsystem. The README is added later, as it references details only added in later commits. Many many more people than the folks named below have contributed with feedback, work on semi-independent patches etc. E.g. various folks have contributed patches to use the read stream infrastructure (added by Thomas in `b5a9b18cd0`) in more places. Similarly, a lot of folks have contributed to the CI infrastructure, which I had started to work on to make adding AIO feasible. Some of the work by contributors has gone into the "v1" prototype of AIO, which heavily influenced the current design of the AIO subsystem. None of the code from that directly survives, but without the prototype, the current version of the AIO infrastructure would not exist. Similarly, the reviewers below have not necessarily looked at the current design or the whole infrastructure, but have provided very valuable input. I am to blame for problems, not they. Author: Andres Freund <andres@anarazel.de> Co-authored-by: Thomas Munro <thomas.munro@gmail.com> Co-authored-by: Nazir Bilal Yavuz <byavuz81@gmail.com> Co-authored-by: Melanie Plageman <melanieplageman@gmail.com> Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi> Reviewed-by: Noah Misch <noah@leadboat.com> Reviewed-by: Jakub Wartak <jakub.wartak@enterprisedb.com> Reviewed-by: Melanie Plageman <melanieplageman@gmail.com> Reviewed-by: Robert Haas <robertmhaas@gmail.com> Reviewed-by: Dmitry Dolgov <9erthalion6@gmail.com> Reviewed-by: Antonin Houska <ah@cybertec.at> Discussion: https://postgr.es/m/uvrtrknj4kdytuboidbhwclo4gxhswwcpgadptsjvjqcluzmah%40brqs62irg4dt Discussion: https://postgr.es/m/20210223100344.llw5an2aklengrmn@alap3.anarazel.de Discussion: https://postgr.es/m/stj36ea6yyhoxtqkhpieia2z4krnam7qyetc57rfezgk4zgapf@gcnactj4z56m		9 months ago
.github	Add CODE_OF_CONDUCT.md, CONTRIBUTING.md, and SECURITY.md.	2 years ago
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README.md

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.

General documentation about this version of PostgreSQL can be found at https://www.postgresql.org/docs/devel/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/devel/installation.html.

The latest version of this software, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.