Re: Direct I/O

On Tue, Nov 01, 2022 at 08:36:18PM +1300, Thomas Munro wrote:
> Hi,
>
> Here is a patch to allow PostgreSQL to use $SUBJECT. It is from the
> AIO patch-set[1]. It adds three new settings, defaulting to off:
>
> io_data_direct = whether to use O_DIRECT for main data files
> io_wal_direct = ... for WAL
> io_wal_init_direct = ... for WAL-file initialisation

You added 3 booleans, but I wonder if it's better to add a string GUC
which is parsed for comma separated strings. (By "better", I mean
reducing the number of new GUCs - which is less important for developer
GUCs anyway.)

DIO is slower, but not so much that it can't run under CI. I suggest to
add an 099 commit to enable the feature during development.

Note that this fails under linux with fsanitize=align:
../src/backend/storage/file/buffile.c:117:17: runtime error: member access within misaligned address 0x561a4a8e40f8 for type 'struct BufFile', which requires 4096 byte alignment

--
Justin