| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | pgsql-hackers(at)postgresql(dot)org, John Naylor <john(dot)naylor(at)2ndquadrant(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
| Subject: | Re: Unhappy about API changes in the no-fsm-for-small-rels patch |
| Date: | 2019-04-16 19:24:30 |
| Message-ID: | 5654.1555442670@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Andres Freund <andres(at)anarazel(dot)de> writes:
> On 2019-04-16 14:31:25 -0400, Tom Lane wrote:
>> This can only work at all if an inaccurate map is very fail-soft,
>> which I'm not convinced it is
> I think it better needs to be fail-soft independent of this the no-fsm
> patch. Because the fsm is not WAL logged etc, it's pretty easy to get a
> pretty corrupted version. And we better deal with that.
Yes, FSM has to be fail-soft from a *correctness* viewpoint; but it's
not fail-soft from a *performance* viewpoint. It can take awhile for
us to self-heal a busted map. And this fake map spends almost all its
time busted and in need of (expensive) corrections. I think this may
actually be the same performance complaint you're making, in different
words.
regards, tom lane
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