| From: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, pgsql-hackers(at)postgresql(dot)org, Daniel Farina <daniel(at)heroku(dot)com> |
| Subject: | Re: Sync Rep v17 |
| Date: | 2011-03-01 18:18:27 |
| Message-ID: | 1299003507.1974.0.camel@ebony |
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| Lists: | pgsql-hackers |
On Tue, 2011-03-01 at 10:02 -0500, Tom Lane wrote:
> Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:
> > On Tue, 2011-03-01 at 15:51 +0900, Fujii Masao wrote:
> >> A spinlock can be used only for very short-term operation like
> >> read/write of some shared-variables. The operation on the queue
> >> is not short, so should be protected by LWLock, I think.
>
> > There's no need to sleep while holding locks and the operations are very
> > short in most cases. The code around it isn't trivial, but that's no
> > reason to use LWlocks.
>
> What does "in most cases" mean?
>
> > LWlocks are just spinlocks plus sem sleeps, so I don't see the need for
> > that in the current code. Other views welcome.
>
> Simon, that is absolutely NOT acceptable. Spinlocks are to be used only
> for short straight-line code segments. If the lock has any potential to
> be held for more than nanoseconds, use an LWLock. The contention costs
> of the shortcut you propose are too high.
No problem to change.
--
Simon Riggs http://www.2ndQuadrant.com/books/
PostgreSQL Development, 24x7 Support, Training and Services
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