Re: New option for pg_basebackup, to specify a different directory for pg_xlog - Mailing list pgsql-hackers

On 18 November 2013 18:45 Fujii Masao wrote:
> On Mon, Nov 18, 2013 at 6:31 PM, Haribabu kommi
> <haribabu.kommi@huawei.com> wrote:
> >
> > On 18 November 2013 11:19 Haribabu kommi wrote:
> >> On 17 November 2013 00:55 Fujii Masao wrote:
> >> > On Sat, Nov 16, 2013 at 2:27 PM, Haribabu kommi
> >> > <haribabu.kommi@huawei.com> wrote:
> >> > > on 15 November 2013 17:26 Magnus Hagander wrote:
> >> > >
> >> > >>On Fri, Nov 15, 2013 at 12:10 PM, Haribabu kommi
> >> > >><haribabu.kommi@huawei.com> wrote:
> >> > >
> >> > >>On 14 November 2013 23:59 Fujii Masao wrote:
> >> > >>> On Thu, Nov 14, 2013 at 9:08 PM, Haribabu kommi
> >> > >>> <haribabu.kommi@huawei.com> wrote:
> >> > >>> > Please find attached the patch, for adding a new option for
> >> > >>> > pg_basebackup, to specify a different directory for pg_xlog.
> >> > >>>>
> >> > >>> Sounds good! Here are the review comments:
> >> > >>>> Don't we need to prevent users from specifying the same
> >> directory
> >> > >>>> in both --pgdata and --xlogdir?
> >> > >
> >> > >>>I feel no need to prevent, even if user specifies both --pgdata
> >> and
> >> > >>>--xlogdir as same directory all the transaction log files will
> >> > >>>be created in the base directory  instead of pg_xlog directory.
> >> > >
> >> > >
> >> > >
> >> > >>Given how easy it would be to prevent that, I think we should.
> It
> >> > >>would be  an easy misunderstanding to specify that when you
> >> actually
> >> > >>want it in  <wherever>/pg_xlog. Specifying that would be
> >> > >>redundant in the first place,  but people ca do that, but it
> >> > >
> >> > >>would also be very easy to do it by mistake, and you'd end up
> >> > >>with something that's really bad, including a recursive symlink.
> >> > >
> >> > >
> >> > >
> >> > > Presently with initdb also user can specify both data and xlog
> >> > > directories as same.
> >> > >
> >> > > To prevent the data directory and xlog directory as same, there
> >> > > is
> >> a
> >> > > way in windows (_fullpath api) to get absolute path from a
> >> > > relative path, but I didn't get any such possibilities in linux.
> >> > >
> >> > > I didn't find any other way to check it, if anyone have any idea
> >> > > regarding this please let me know.
> >> >
> >> > What about make_absolute_path() in miscinit.c?
> >>
> >> The make_absoulte_patch() function gets the current working
> directory
> >> and adds The relative path to CWD, this is not giving proper
> absolute
> >> path.
> >>
> >> I have added a new function verify_data_and_xlog_dir_same() which
> >> will change the Current working directory to data directory and gets
> >> the CWD and the same way for transaction log directory. Compare the
> >> both data and xlog directories and throw an error. Please check it
> once.
> >>
> >> Is there any other way to identify that both data and xlog
> >> directories are pointing to the same Instead of comparing both
> absolute paths?
> >>
> >> Updated patch attached in the mail.
> >
> > Failure when the xlogdir doesn't exist is fixed in the updated patch
> attached in the mail.
>
> Thanks for updating the patch!
>
> With the patch, when I specify the same directory in both -D and --
> xlogdir, I got the following error.
>
> $ cd /tmp
> $ pg_basebackup -D hoge --xlogdir=/tmp/hoge -X fetch
> pg_basebackup: could not change directory to "hoge": No such file or
> directory

Thanks. After finding the xlog directory absolute path returning back to current working
Directory is missed, because of this reason it is failing while finding the absolute
Path for data directory. Apart from this change the code is reorganized a bit.

Updated patch is attached in the mail. Please review it once.

Regards,
Hari babu.