Thomas Munro faeedbcefd Introduce PG_IO_ALIGN_SIZE and align all I/O buffers. ... In order to have the option to use O_DIRECT/FILE_FLAG_NO_BUFFERING in a later commit, we need the addresses of user space buffers to be well aligned. The exact requirements vary by OS and file system (typically sectors and/or memory pages). The address alignment size is set to 4096, which is enough for currently known systems: it matches modern sectors and common memory page size. There is no standard governing O_DIRECT's requirements so we might eventually have to reconsider this with more information from the field or future systems. Aligning I/O buffers on memory pages is also known to improve regular buffered I/O performance. Three classes of I/O buffers for regular data pages are adjusted: (1) Heap buffers are now allocated with the new palloc_aligned() or MemoryContextAllocAligned() functions introduced by commit 439f6175. (2) Stack buffers now use a new struct PGIOAlignedBlock to respect PG_IO_ALIGN_SIZE, if possible with this compiler. (3) The buffer pool is also aligned in shared memory. WAL buffers were already aligned on XLOG_BLCKSZ. It's possible for XLOG_BLCKSZ to be configured smaller than PG_IO_ALIGNED_SIZE and thus for O_DIRECT WAL writes to fail to be well aligned, but that's a pre-existing condition and will be addressed by a later commit. BufFiles are not yet addressed (there's no current plan to use O_DIRECT for those, but they could potentially get some incidental speedup even in plain buffered I/O operations through better alignment). If we can't align stack objects suitably using the compiler extensions we know about, we disable the use of O_DIRECT by setting PG_O_DIRECT to 0. This avoids the need to consider systems that have O_DIRECT but can't align stack objects the way we want; such systems could in theory be supported with more work but we don't currently know of any such machines, so it's easier to pretend there is no O_DIRECT support instead. That's an existing and tested class of system. Add assertions that all buffers passed into smgrread(), smgrwrite() and smgrextend() are correctly aligned, unless PG_O_DIRECT is 0 (= stack alignment tricks may be unavailable) or the block size has been set too small to allow arrays of buffers to be all aligned. Author: Thomas Munro <thomas.munro@gmail.com> Author: Andres Freund <andres@anarazel.de> Reviewed-by: Justin Pryzby <pryzby@telsasoft.com> Discussion: https://postgr.es/m/CA+hUKGK1X532hYqJ_MzFWt0n1zt8trz980D79WbjwnT-yYLZpg@mail.gmail.com		2023-04-08 16:34:50 +12:00
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expected
sql
t	Update copyright for 2023	2023-01-02 15:00:37 -05:00
.gitignore
blcost.c	Update copyright for 2023	2023-01-02 15:00:37 -05:00
blinsert.c	Introduce PG_IO_ALIGN_SIZE and align all I/O buffers.	2023-04-08 16:34:50 +12:00
bloom--1.0.sql
bloom.control
bloom.h	Update copyright for 2023	2023-01-02 15:00:37 -05:00
blscan.c	Update copyright for 2023	2023-01-02 15:00:37 -05:00
blutils.c	Convert many uses of ReadBuffer[Extended](P_NEW) to ExtendBufferedRel()	2023-04-05 18:57:29 -07:00
blvacuum.c	Update copyright for 2023	2023-01-02 15:00:37 -05:00
blvalidate.c	Update copyright for 2023	2023-01-02 15:00:37 -05:00
Makefile
meson.build	Update copyright for 2023	2023-01-02 15:00:37 -05:00