| From: | Jeff Davis <pgsql(at)j-davis(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Joachim Wieland <joe(at)mcknight(dot)de>, Greg Smith <greg(at)2ndquadrant(dot)com>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, "Florian G(dot) Pflug" <fgp(at)phlo(dot)org>, Josh Berkus <josh(at)agliodbs(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Listen / Notify - what to do when the queue is full |
| Date: | 2010-01-20 00:19:21 |
| Message-ID: | 1263946761.13109.32.camel@monkey-cat.sm.truviso.com |
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| Lists: | pgsql-hackers |
On Tue, 2010-01-19 at 19:05 -0500, Tom Lane wrote:
> I guess Joachim is trying to provide a similar guarantee for the new
> implementation, but I'm not clear on why it would require locking.
> The new implementation is broadcast and ISTM it shouldn't require the
> modifying transaction to know which processes are listening.
I think there is a better way. I'll dig into it a little more.
> I haven't read the patch but I agree that the description you give is
> pretty scary from a performance standpoint. More locks around
> transaction commit doesn't seem like a good idea.
I was also worried about holding multiple LWLocks at once -- is such
practice generally avoided in the rest of the code?
> If they're only taken
> when an actual LISTEN or NOTIFY has happened in the current transaction,
> that'd be okay (certainly no worse than what happens now) but the naming
> suggested that this'd happen unconditionally.
It appears that the locks are only taken when LISTEN or NOTIFY is
involved.
Regards,
Jeff Davis
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