Re: binary logs: a location other than pg_xlog??

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От Tom Lane
Тема Re: binary logs: a location other than pg_xlog??
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Msg-id 14940.1290453941@sss.pgh.pa.us
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Ответ на Re: binary logs: a location other than pg_xlog??  ("Kevin Grittner" <Kevin.Grittner@wicourts.gov>)
Ответы Re: binary logs: a location other than pg_xlog??  ("Kevin Grittner" <Kevin.Grittner@wicourts.gov>)
Re: binary logs: a location other than pg_xlog??  (James Cloos <cloos@jhcloos.com>)
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"Kevin Grittner" <Kevin.Grittner@wicourts.gov> writes:
> James Cloos <cloos@jhcloos.com> wrote:
>> I notice that everyone suggests using a symlink, but I never see
>> anyone suggest just mounting a filesystem there.

> I think initdb wants an empty directory.  Once it creates the
> directory structure with pg_xlog, if that's a mount point, it's a
> bit awkward to mount there and then copy from behind the mount point
> onto it.  A symbolic link seems both safer and easier.

Well, either way you're going to have to modify things after initdb.

The notion of mounting a filesystem directly there scares me, on the
whole.  Here is the problem: what if someday that filesystem happens not
to be mounted?  Then you have a bare mountpoint directory, with no real
way for the postmaster to notice that that wasn't what you intended.
Hilarity ensues.  (You might want to go back a few years in the archives
and read Joe Conway's report of what happened to his DB when a soft NFS
mount was a bit slow to mount one day.  The symptoms for a missing
pg_xlog directory would be different but not better.)  A symlink seems
to have a bit more error detection capability built in, especially if
you don't symlink to exactly the filesystem mount point but rather a
directory level or two down, so that the target dir is not there if the
mount fails.

            regards, tom lane

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