Comment 1 for bug 1286114
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| Raghavendra D Prabhu (raghavendra-prabhu) wrote Re: Slow file extend when innodb_use_fallocate=1 and SSD file storage. | #1 |
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67d34a1
(Get the code!)
@Jan,
Yes, it does look like offset is always taken to be 0 unconditionally
(in os_file_set_size). However, regarding the I/O, fallocate (which
posix_fallocate does unless fallocate is unavailable) is a no-op for the
already written/allocated parts of the file (ie, it won't zero out any
written data), thus the offset shouldn't harm here (unless the filesytem
did something awry here). Also, since fallocate doesn't involve
any I/O (due to lazy extent allocation), it shouldn't add to
added I/O pressure.
However, there is other side to posix_fallocate, where it falls
back to pwrite on filesystems/kernels where it is not supported
(say, tmpfs, for which it was added in 2011 or so), here, it may
end up doing I/O; but here again, it shouldn't do anything to
already written data (as per specs of posix_fallocate), so the
I/O should be same as extending from that offset.
In SSD case, which filesystem/kernel combinations were in use?