denoland
`Deno.open()` does not support O_DIRECT for performing Direct I/O
Direct I/O is important for disabling the kernel block-cache, in the event your application manages such caching itself. Without O_DIRECT, you wind up with double-buffering.
O_DIRECT (since Linux 2.4.10)
Try to minimize cache effects of the I/O to and from this
file. In general this will degrade performance, but it is
useful in special situations, such as when applications do
their own caching. File I/O is done directly to/from
user-space buffers. The O_DIRECT flag on its own makes an
effort to transfer data synchronously, but does not give
the guarantees of the O_SYNC flag that data and necessary
metadata are transferred. To guarantee synchronous I/O,
O_SYNC must be used in addition to O_DIRECT. See NOTES
below for further discussion.
A semantically similar (but deprecated) interface for
block devices is described in raw(8).
I propose adding a new flag to Deno.OpenOptions, named direct.
On Linux, this should apply the O_DIRECT flag.
On Windows, this should apply FILE_FLAG_WRITE_THROUGH + FILE_FLAG_NO_BUFFERING:
- https://learn.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilea#caching_behavior
The flags FILE_FLAG_WRITE_THROUGH and FILE_FLAG_NO_BUFFERING are independent and may be combined.
If FILE_FLAG_WRITE_THROUGH is used but FILE_FLAG_NO_BUFFERING is not also specified, so that system caching is in effect, then the data is written to the system cache but is flushed to disk without delay.
If FILE_FLAG_WRITE_THROUGH and FILE_FLAG_NO_BUFFERING are both specified, so that system caching is not in effect, then the data is immediately flushed to disk without going through the Windows system cache. The operating system also requests a write-through of the hard disk's local hardware cache to persistent media.
