Re: pg_basebackup fails if a data file is removed

On Fri, Dec 21, 2012 at 2:28 PM, Heikki Linnakangas
<hlinnakangas@vmware.com> wrote:
> When pg_basebackup copies data files, it does basically this:
>
>> if (lstat(pathbuf, &statbuf) != 0)
>> {
>>         if (errno != ENOENT)
>>                 ereport(ERROR,
>>                                 (errcode_for_file_access(),
>>                                  errmsg("could not stat file or directory
>> \"%s\": %m",
>>                                         pathbuf)));
>>
>>         /* If the file went away while scanning, it's no error. */
>>         continue;
>> }
>
>> ...
>> sendFile(pathbuf, pathbuf + basepathlen + 1, &statbuf);
>
> There's a race condition there. If the file is removed after the lstat call,
> and before sendFile opens the file, the backup fails with an error. It's a
> fairly tight window, so it's difficult to run into by accident, but by
> putting a breakpoint with a debugger there it's quite easy to reproduce, by
> e.g doing a VACUUM FULL on the table about to be copied.
>
> A straightforward fix is to allow sendFile() to ignore ENOENT. Patch
> attached.

Looks good to me. Nice spot - don't tell me you actually ran into it
during testing? :)

--
 Magnus Hagander
 Me: http://www.hagander.net/
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