Re: heavily contended lwlocks with long wait queues scale badly

On Mon, Nov 21, 2022 at 10:31:14AM -0500, Jonathan S. Katz wrote:
> On 11/20/22 2:56 PM, Andres Freund wrote:
>> I still think it might be worth to backpatch in a bit, but so far the votes on
>> that weren't clear enough on that to feel comfortable.
> 
> My general feeling is "yes" on backpatching, particularly if this is a bug
> and it's fixable without ABI breaks.

Now that commit a4adc31 has had some time to bake and concerns about
unintended consequences may have abated, I wanted to revive this
back-patching discussion.  I see a few possibly-related reports [0] [1]
[2], and I'm now seeing this in the field, too.  While it is debatable
whether this is a bug, it's a quite nasty issue for users, and it's both
difficult to detect and difficult to work around.

Thoughts?

[0] https://postgr.es/m/CAM527d-uDn5osa6QPKxHAC6srOfBH3M8iXUM%3DewqHV6n%3Dw1u8Q%40mail.gmail.com
[1] https://postgr.es/m/VI1PR05MB620666631A41186ACC3FC91ACFC70%40VI1PR05MB6206.eurprd05.prod.outlook.com
[2] https://postgr.es/m/dd0e070809430a31f7ddd8483fbcce59%40mail.gmail.com

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Nathan Bossart
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