Daniel Ng <[email protected]> writes:
> I am trying to enable the direct IO for the disk-resident
> hash partitions of hashjoin in postgresql.
Why would you think that's a good idea?
> Can anyone advise what's the reason and how to fix this?
Per the open(2) man page:
The O_DIRECT flag may impose alignment restrictions on the length and
address of userspace buffers and the file offset of I/Os. In Linux
alignment restrictions vary by file system and kernel version and might
be absent entirely. However there is currently no file system-indepen-
dent interface for an application to discover these restrictions for a
given file or file system.
It's unlikely that the code you're hacking makes any attempt to align
the buffers it's using to read/write files.
regards, tom lane
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