作者
digoal
日期
2021-07-19
标签
PostgreSQL , direct I/O , wal
背景
仅仅当wal=minimal , max_wal_senders=0时支持dio, 为什么呢?
因为如果写入的wal要被立即读出, 还是开cache快点, 例如有standby时, 需要在wal写入后立即读出, 开cache更快.
```
man fcntl
F_NOCACHE Turns data caching off/on. A non-zero value in arg turns data caching off. A value of zero in arg turns data caching on.
```
https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=2dbe8905711ba09a2214b6e835f8f0c2c4981cb3
```
Support direct I/O on macOS. master github/master
author Thomas Munro tmunro@postgresql.org
Sun, 18 Jul 2021 20:52:00 +0000 (08:52 +1200)
committer Thomas Munro tmunro@postgresql.org
Sun, 18 Jul 2021 23:01:01 +0000 (11:01 +1200)
commit 2dbe8905711ba09a2214b6e835f8f0c2c4981cb3
tree 775e44cb05c4dfa8f12e68eb388f04e9aa252c96 tree
parent f157db862225a7bfe041ca3f7b73e913e2a8d8d6 commit | diff
Support direct I/O on macOS.
Macs don't understand O_DIRECT, but they can disable caching with a
separate fcntl() call. Extend the file opening functions in fd.c to
handle this for us if the caller passes in PG_O_DIRECT.
For now, this affects only WAL data and even then only if you set:
max_wal_senders=0
wal_level=minimal
This is not expected to be very useful on its own, but later proposed
patches will make greater use of direct I/O, and it'll be useful for
testing if developers on Macs can see the effects.
Reviewed-by: Andres Freund andres@anarazel.de
Discussion: https://postgr.es/m/CA%2BhUKG%2BADiyyHe0cun2wfT%2BSVnFVqNYPxoO6J9zcZkVO7%2BNGig%40mail.gmail.com
```
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