| From: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)2ndquadrant(dot)com> |
| Cc: | Jim Nasby <jim(at)nasby(dot)net>, Robert Haas <robertmhaas(at)gmail(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, Fabrízio Mello <fabriziomello(at)gmail(dot)com>, Pgsql Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: GSoC proposal - "make an unlogged table logged" |
| Date: | 2014-04-03 10:38:29 |
| Message-ID: | 533D3A25.8020901@vmware.com |
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| Thread: | |
| Lists: | pgsql-hackers |
On 04/01/2014 08:58 PM, Andres Freund wrote:
> On 2014-04-01 12:56:04 -0500, Jim Nasby wrote:
>> On 3/4/14, 8:50 AM, Andres Freund wrote:
>>> Can't that be solved by just creating the permanent relation in a new
>>> relfilenode? That's equivalent to a rewrite, yes, but we need to do that
>>> for anything but wal_level=minimal anyway.
>>
>> Maybe I'm missing something, but doesn't this actually involve writing the data twice? Once into WAL and again into the relation itself?
>
> Yes. But as I said, that's unavoidable for anything but
> wal_level=minimal.
Ideally, you would *only* write the data to WAL, when you do ALTER TABLE
... SET LOGGED. There's no fundamental reason you need to rewrite the
heap, too. I understand that it might be difficult to do, because of the
way the system catalogs work, but it's worthy goal.
- Heikki
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