Re: [GSoC2014] Patch ALTER TABLE ... SET LOGGED

<div dir="ltr"><div class="gmail_extra"><br />On Fri, Aug 22, 2014 at 4:45 PM, Alvaro Herrera <<a
href="mailto:alvherre@2ndquadrant.com">alvherre@2ndquadrant.com</a>>wrote:<br />><br />> > 2. The patch
seemsto think that it can sometimes be safe to change<br /> > > the relpersistence of an existing relation.
 Unlessyou can be sure<br />> > that no buffers can possibly be present in shared_buffers and nobody<br />>
>will use an existing relcache entry to read a new one in, it's not,<br /> > > because the buffers won't have
theright BM_PERSISTENT marking.  I'm<br />> > very nervous about the fact that this patch seems not to have
touched<br/>> > bufmgr.c, but maybe I'm missing something.<br /> ><br />> Right.  Andres pointed this out
previously,and the patch was updated<br />> consequently.  The only remaining case in which we do that, again
AFAIR,<br/>> is for indexes, just after the table has been rewritten and just before<br /> > the indexes are
reindexed. There should be no buffer access of the old<br />> indexes at that point, so there would be no buffer
markedwith the wrong<br />> flag.  Also, the table is locked access-exclusively (is that a word?),<br /> > so no
othertransaction could possibly be reading buffers for its<br />> indexes.<br />><br />> I pointed out, in the
emailjust before pushing the patch, that perhaps<br />> we should pass down the new relpersistence flag into
finish_heap_swap,<br/> > and from there we could pass it down to reindex_index() which is where<br />> it would
beneeded.  I'm not sure it's worth the trouble, but I think we<br />> can still ask Fabrizio to rework that part.<br
/>><br/> > Maybe it is me missing something.<br />><br />> BTW why is it that index_build() checks the
heap'srelpersistence flag<br />> rather than the index'?<br />><br /><br /></div><div class="gmail_extra">I can
reworkthis part if it's a real concern.<br /></div><div class="gmail_extra"><br /></div><div
class="gmail_extra">Regards,<br/></div><div class="gmail_extra"><br />--<br />Fabrízio de Royes Mello<br
/>Consultoria/CoachingPostgreSQL<br />>> Timbira: <a
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