| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Heikki Linnakangas <hlinnaka(at)iki(dot)fi> |
| Cc: | Alvaro Herrera <alvherre(at)dcc(dot)uchile(dot)cl>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>, Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Shared row locking |
| Date: | 2004-12-19 21:22:46 |
| Message-ID: | 16664.1103491366@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Heikki Linnakangas <hlinnaka(at)iki(dot)fi> writes:
> On Sun, 19 Dec 2004, Alvaro Herrera wrote:
>> This is not useful at all, because the objective of this exercise is to
>> downgrade locks, from exclusive row locking (SELECT ... FOR UPDATE) to
>> shared row locking.
> Actually it might help in some scenarios. Remember, we're not talking
> about upgrading shared locks to exclusive locks. We're only talking about
> locking more rows than necessary (all rows).
Nonetheless, it would mean that locks would be taken depending on
implementation-dependent, not-visible-to-the-user considerations.
Shared locks can still cause deadlocks, and so you would have an
unreliable application, which would only be unreliable under load.
As I said in connection with the other proposal, weird user-visible
semantics should be the last resort not the first.
regards, tom lane
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