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Re: svn commit: r1073366 - in /subversion/trunk: notes/wc-ng/pristine-store subversion/libsvn_wc/wc-queries.sql subversion/libsvn_wc/wc_db_pristine.c

From: Julian Foad <julianfoad_at_btopenworld.com>
Date: Tue, 15 Mar 2011 13:49:57 +0000

Ivan Zhakov wrote:
> On Tue, Mar 1, 2011 at 21:13, Julian Foad <julian.foad_at_wandisco.com> wrote:
> > Bert Huijben wrote:
> >> > -----Original Message-----
> >> > From: Julian Foad [mailto:julian.foad_at_wandisco.com]
> >> >
> >> > I'm not clear exactly what problem we would avoid by eliminating the
> >> > "select a unique name" step of this process. Is it what I describe
> >> > below at the end of note [1] - that a scanner might be more likely to
> >> > re-scan the content, and therefore more likely to cause a delay?
> >>
> >> No, the problem I try to avoid is
> >> * you create a file
> >> <virus scanner opens the file to verify that it is not a virus>
> >> * you delete the file (after the virusscanner releases the file)
> >> * you rename a file to be at the old location
> >>
> >> While we really need something like
> >> * rename to a unique name.
> >> <virusscanner ignores the file, because it was already scanned at the original location>
> >
> > >From discussing on IRC we agree that the main concern is that this
> > involves too many separate filesystem operations, rather than any
> > specific problem with a particular step.
> >
> > I have committed it as is in r1075942, and would like to improve it as a
> > follow-up.
> >
> > Options for improvement:
> >
> > (a) Don't open a pristine file with FILE_SHARE_DELETE. Instead,
> > accept that an attempt to delete it may fail, and if that happens, leave
> > the there as an orphan. When adding a pristine file, if it already
> > exists on disk then just keep the copy that already exists. When
> > cleaning up orphan files, if a delete fails, just leave the file there.
> > Consider implementing automatic clean-up to prevent orphan files from
> > accumulating indefinitely.
> >
> > (b) Find or write a "rename to a unique name" function that operates
> > in a single step instead of a creating a new file and then overwriting
> > it.
> >
> > (c) Don't rename the file before deleting it; instead, just delete it.
> > On Windows, when adding a new file, if a file with that name already
> > exists, *then* rename the existing file before moving the new file into
> > place. (We can't just keep the existing file because it is pending
> > deletion and will disappear when the reader finishes reading it.)
> >
> > Pros and cons:
> >
> > (a) This would reduce the number of file system operations to a
> > minimum. It would involve bypassing APR to avoid the FILE_SHARE_DELETE
> > flag, which is not ideal but possible.
> >
> > (b) This would remove one of the file system operations. It would
> > involve writing a function similar to APR's fall-back implementation of
> > apr_file_mktemp() that exists for systems that do not provide a
> > "mkstemp" system API. I'm not sure if there are any concrete problems
> > with doing this sort of thing in "user space".
> >
> > (c) This would remove two of the file system operations. It sounds
> > straightforward.
> >
> > Comments?
> >
>
> (b) Is best option for.

For ... what?

> It should be big problem to generate random
> name using current time and then try rename file to this name. Repeat
> on error.

I assume you mean "it should not be a big problem...".

- Julian
Received on 2011-03-15 14:50:33 CET

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