On Wed, Jul 16, 2025 at 4:46 PM Andres Freund <and...@anarazel.de> wrote: > Currently the API wouldn't easily allow the table AM to do batched TID lookups > - if you have a query that looks at a lot of table tuples in the same buffer > consecutively, we spend a lot of time locking/unlocking said buffer. We also > spend a lot of time dispatching from nodeIndexscan.c to tableam in such > queries. > > I'm not suggesting to increase the scope to handle that, but it might be worth > keeping in mind. > > I think the potential gains here are really substantial.
I agree. I've actually discussed this possibility with Tomas a few times, though not recently. It's really common for TIDs that appear on a leaf page to be slightly out of order due to minor heap fragmentation. Even minor fragmentation can significantly increase pin/buffer lock traffic right now. I think that it makes a lot of sense for the general design to open up possibilities such as this. > I see some slowdown for well-cached queries with the patch, I've not dug into > why. I saw less than a 5% regression in pgbench SELECT with the "complex" patch with 32 clients. My guess is that it's due to the less efficient memory allocation with batching. Obviously this isn't acceptable, but I'm not particularly concerned about it right now. I was actually pleased to see that there wasn't a much larger regression there. -- Peter Geoghegan
