| From: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
|---|---|
| To: | Noah Misch <noah(at)leadboat(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: ALTER TABLE lock strength reduction patch is unsafe |
| Date: | 2012-01-02 18:41:31 |
| Message-ID: | CA+U5nMJmHizgiH2TZQWvxftMYjT1Td-WLHB5-PsaoSVQeh9cBA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Mon, Jan 2, 2012 at 6:06 PM, Noah Misch <noah(at)leadboat(dot)com> wrote:
> On Mon, Jan 02, 2012 at 05:09:16PM +0000, Simon Riggs wrote:
>> Attached patch makes SnapshotNow into an MVCC snapshot, initialised at
>> the start of each scan iff SnapshotNow is passed as the scan's
>> snapshot. It's fairly brief but seems to do the trick.
>
> That's a neat trick. However, if you start a new SnapshotNow scan while one is
> ongoing, the primordial scan's snapshot will change mid-stream.
Do we ever do that? (and if so, Why?!? or perhaps just Where?)
We can use more complex code if required, but we'll be adding
complexity and code into the main path that I'd like to avoid.
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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