| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Fabrízio de Royes Mello <fabriziomello(at)gmail(dot)com>, Andres Freund <andres(at)2ndquadrant(dot)com>, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Thom Brown <thom(at)linux(dot)com>, Christoph Berg <cb(at)df7cb(dot)de>, Pgsql Hackers <pgsql-hackers(at)postgresql(dot)org>, Stephen Frost <sfrost(at)snowman(dot)net> |
| Subject: | Re: [GSoC2014] Patch ALTER TABLE ... SET LOGGED |
| Date: | 2014-08-22 20:54:38 |
| Message-ID: | 7883.1408740878@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> 2. The patch seems to think that it can sometimes be safe to change
> the relpersistence of an existing relation. Unless you can be sure
> that no buffers can possibly be present in shared_buffers and nobody
> will use an existing relcache entry to read a new one in, it's not,
> because the buffers won't have the right BM_PERSISTENT marking. I'm
> very nervous about the fact that this patch seems not to have touched
> bufmgr.c, but maybe I'm missing something.
Maybe I misunderstood something, but I had the impression that this was
handled by assigning a new relfilenode (and hence copying all the data).
So the buffers with one marking would be disjoint from the ones with the
other marking.
regards, tom lane
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