On Tue, Nov 7, 2017 at 12:11 PM, Raphael Hertzog <raphael@xxxxxxxxx> wrote:
> Hello Amir,
>
> Le samedi 04 novembre 2017, Amir Goldstein a écrit :
>> I tries mounting squashfs+overlayfs to /var/lib/postgresql and create
>> db on Ubuntu and it seemed ok.
>
> FWIW, in my failing case, it uses PostgreSQL 10.0 as in Debian
> Testing/Unstable. In Ubuntu, it's only available in Bionic Beaver (development
> release).
And is this the same PostgreSQL version that worked with kernel v4.12.6?
[...]
> As for strace output, postgresql is split over multiple processes. The one that
> generates the error in the log is 31599 (checkpointer process). I also attach
> some file listing of the directories that it fails to fsync. strace looks like
> this (in loop):
>
> # strace -f -p 31599
> select(0, NULL, NULL, NULL, {tv_sec=1, tv_usec=0}) = 0 (Timeout)
> rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
> open("pg_xact", O_RDONLY) = 3
> fsync(3) = 0
> close(3) = 0
> open("pg_commit_ts", O_RDONLY) = 3
> fsync(3) = -1 EINVAL (Invalid argument)
The reason for the error is quite straight forward.
open O_RDONLY gets an open file on lower read-only squashfs
that doesn't have an fsync operation, so fsync returns EINVAL as per
the man page documentation:
EROFS, EINVAL
fd is bound to a special file which does not support
synchronization.
The question is why do you see this error only now.
There is nothing I know of that changed in overlayfs which could explain
why this behavior has not been the same forever.
CC'ing Jeff, because his fsync error reporting infrastructure was merged to
kernel v4.13 where you report the alleged regression, but I didn't find how
his changes could have changed this behavior, as EINVAL is returned right
in the entry of the fsync system call.
int vfs_fsync_range(struct file *file, loff_t start, loff_t end, int datasync)
{
struct inode *inode = file->f_mapping->host;
if (!file->f_op->fsync)
return -EINVAL;
Perhaps this a PostgreSQL regression (when storing db on overlayfs/squashfs)
that should be reported to PostgreSQL developers?
Working around this in kernel is possible, but requires overriding
file_operations
for all overlay regular files. Not a small change, but we might want
to do it for
other reasons anyway.
Thanks,
Amir.
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