Re: heavily contended lwlocks with long wait queues scale badly

On 1/10/24 10:45 PM, Michael Paquier wrote:
> On Wed, Jan 10, 2024 at 09:17:47PM -0600, Nathan Bossart wrote:
>> 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.
>
> +1, I've seen this becoming a PITA for a few things. Knowing that the
> size of PGPROC does not change at all, I would be in favor for a
> backpatch, especially since it's been in the tree for more than 1
> year, and even more knowing that we have 16 released with this stuff
> in.

I have similar data sources to Nathan/Michael and I'm trying to avoid
piling on, but one case that's interesting occurred after a major
version upgrade from PG10 to PG14 on a database supporting a very
active/highly concurrent workload. On inspection, it seems like
backpatching would help this particularly case.

With 10/11 EOL, I do wonder if we'll see more of these reports on
upgrade to < PG16.

(I was in favor of backpatching prior; opinion is unchanged).

Thanks,

Jonathan