Re: WAL Insertion Lock Improvements

Hi,

On 2023-07-25 16:43:16 +0900, Michael Paquier wrote:
> On Sat, Jul 22, 2023 at 01:08:49PM +0530, Bharath Rupireddy wrote:
> > Yes, it looks safe to me too.
> 
> 0001 has been now applied.  I have done more tests while looking at
> this patch since yesterday and was surprised to see higher TPS numbers
> on HEAD with the same tests as previously, and the patch was still
> shining with more than 256 clients.

Just a small heads up:

I just rebased my aio tree over the commit and promptly, on the first run, saw
a hang. I did some debugging on that. Unfortunately repeated runs haven't
repeated that hang, despite quite a bit of trying.

The symptom I was seeing is that all running backends were stuck in
LWLockWaitForVar(), even though the value they're waiting for had
changed. Which obviously "shouldn't be possible".

It's of course possible that this is AIO specific, but I didn't see anything
in stacks to suggest that.


I do wonder if this possibly exposed an undocumented prior dependency on the
value update always happening under the list lock.

Greetings,

Andres Freund