Hi,
On 2026-01-13 00:58:49 +0100, Tomas Vondra wrote:
> On 1/10/26 02:42, Andres Freund wrote:
> > psql -Xq -c 'SELECT pg_buffercache_evict_all();' -c 'SELECT numa_node, sum(size) FROM pg_shmem_allocations_numa
GROUPBY 1;' && perf stat --per-socket -M memory_bandwidth_read,memory_bandwidth_write -a psql -c 'SELECT sum(abalance)
FROMpgbench_accounts;'
> And then I initialized pgbench with scale that is much larger than
> shared buffers, but fits into RAM. So cached, but definitely > NB/4. And
> then I ran
>
> select * from pgbench_accounts offset 1000000000;
>
> which does a sequential scan with the circular buffer you mention abobe
Did you try it with the query I suggested? One plausible reason why you did
not see an effect with your query is that with a huge offset you actually
never deform the tuple, which is an important and rather latency sensitive
path.
Greetings,
Andres Freund
