| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: unlogged tables vs. GIST |
| Date: | 2010-12-17 20:03:34 |
| Message-ID: | 4788.1292616214@sss.pgh.pa.us |
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Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
> On 17.12.2010 21:32, Robert Haas wrote:
>> I guess the question is whether it's right to conflate "table is
>> unlogged" with "LSN is fake". It's not immediately obvious to me that
>> those concepts are isomorphic, although though the reverse isn't
>> obvious to me either.
> The buffer manager only needs to know if it has to flush the WAL before
> writing the page to disk. The flag just means that the buffer manager
> never needs to do that for this buffer. You're still free to store a
> real LSN there if you want to, it just won't cause any WAL flushes.
Yeah. I think that BM_UNLOGGED might be a poor choice for the flag name,
just because it overstates what the bufmgr needs to assume. It might be
better to reverse the flag sense, and have a new flag that *is* set if
the page contains an LSN that we have to check against WAL.
regards, tom lane
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