| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Mithun Cy <mithun(dot)cy(at)enterprisedb(dot)com>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: [HACKERS] Moving relation extension locks out of heavyweight lock manager |
| Date: | 2018-03-01 20:40:59 |
| Message-ID: | 20180301204059.wfmmzxl52v6rrpb3@alap3.anarazel.de |
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| Lists: | pgsql-hackers |
On 2018-03-01 15:37:17 -0500, Robert Haas wrote:
> On Thu, Mar 1, 2018 at 2:17 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> >> However, if we take the position that no hash collision probability is
> >> low enough and that we must eliminate all chance of false collisions,
> >> except perhaps when the table is full, then we have to make this
> >> locking mechanism a whole lot more complicated. We can no longer
> >> compute the location of the lock we need without first taking some
> >> other kind of lock that protects the mapping from {db_oid, rel_oid} ->
> >> {memory address of the relevant lock}.
> >
> > Hm, that's not necessarily true, is it? Wile not trivial, it also
> > doesn't seem impossible?
>
> You can't both store every lock at a fixed address and at the same
> time put locks at a different address if the one they would have used
> is already occupied.
Right, but why does that require a lock?
Greetings,
Andres Freund
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