Re: Freeze avoidance of very large table.

On Thu, Nov 19, 2015 at 5:54 AM, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:
> On Wed, Nov 18, 2015 at 11:18 AM, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:
>>
>> I get an error when running pg_upgrade from 9.4 to 9.6-this
>>
>> error while copying relation "mediawiki.archive"
>> ("/tmp/data/base/16414/21043_vm" to
>> "/tmp/data_fm/base/16400/21043_vm"): No such file or directory
>
> OK, so the problem seems to be that rewriteVisibilitymap can get
> called with errno already set to a nonzero value.
>
> It never clears it, and then fails at the end despite that no error
> has actually occurred.
>
> Just setting it to 0 at the top of the function seems to be correct
> thing to do. Or does it need to save the old value and restore it?

Thank you for testing!
I think that the former is better, so attached latest patch.

> But now when I want to do the upgrade faster, I run into this:
>
> "This utility cannot upgrade from PostgreSQL version from 9.5 or
> before to 9.6 or later with link mode."
>
> Is this really an acceptable a tradeoff? Surely we can arrange to
> link everything else and rewrite just the _vm, which is a tiny portion
> of the data directory. I don't think that -k promises to link
> everything it possibly can.

I agree.
I've changed the patch so that.
pg_upgarde creates new _vm file and rewrites it even if upgrading to
9.6 with link mode.

Regards,

--
Masahiko Sawada