| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Simon Riggs <simon(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Reduce lock levels for ADD and DROP COLUMN |
| Date: | 2010-12-27 15:41:55 |
| Message-ID: | 14952.1293464515@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Mon, Dec 27, 2010 at 6:42 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>> Idea is to reduce lock level of ADD/DROP COLUMN from AccessExclusiveLock
>> down to ShareRowExclusiveLock.
>>
>> To make it work, we need to recognise that we are adding a column
>> without rewriting the table.
> Can you elaborate on why you think that's the right test? It seems to
> me there could be code out there that assumes that the tuple
> descriptor won't change under it while it holds an AccessShareLock.
s/could/definitely is/
I think this is guaranteed to break stuff; to the point that I'm
not even going to review the proposal in any detail.
regards, tom lane
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