| From: | Claudio Freire <klaussfreire(at)gmail(dot)com> |
|---|---|
| To: | Peter Geoghegan <pg(at)heroku(dot)com> |
| Cc: | Stephen Frost <sfrost(at)snowman(dot)net>, "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>, Dimitri Fontaine <dimitri(at)2ndquadrant(dot)fr>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: DDL Damage Assessment |
| Date: | 2014-10-02 21:04:18 |
| Message-ID: | CAGTBQpbXcM41+ou5qJuQkmr--mjKBpaJ4zB8-T-_LDk72NyYmg@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Thu, Oct 2, 2014 at 6:00 PM, Peter Geoghegan <pg(at)heroku(dot)com> wrote:
>> Granted, it's something that's not easily automatable, whereas a nowait is.
>>
>> However, rather than nowait, I'd prefer "cancellable" semantics, that
>> would cancel voluntarily if any other transaction requests a
>> conflicting lock, like autovacuum does.
>
> I think the problem you'll have with NOWAIT is: you have an error from
> having to wait...what now? Do you restart? I imagine this would
> frequently result in what is effectively lock starvation. Any old
> AccessShareLock-er is going to make our migration tool restart. We'll
> never finish.
I've done that manually (throw the DDL, and cancel if it takes more
than a couple of seconds) on modest but relatively busy servers with
quite some success.
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