Re: BUG #16109: Postgres planning time is high across version - 10.6 vs 10.10

(moved to -hackers)

On Tue, Nov 12, 2019 at 9:55 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> This last point is more oriented towards other PG developers: I wonder
> if we ought to display buffer statistics for plan time, for EXPLAIN
> (BUFFERS). That'd surely make it easier to discern cases where we
> e.g. access the index and scan a lot of the index from cases where we
> hit some CPU time issue. We should easily be able to get that data, I
> think, we already maintain it, we'd just need to compute the diff
> between pgBufferUsage before / after planning.

That would be quite interesting to have. I attach as a reference a
quick POC patch to implement it:

# explain (analyze, buffers) select * from pg_stat_activity;
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------
Hash Left Join (cost=2.25..3.80 rows=100 width=440) (actual
time=0.259..0.276 rows=6 loops=1)
Hash Cond: (s.usesysid = u.oid)
Buffers: shared hit=5
-> Hash Left Join (cost=1.05..2.32 rows=100 width=376) (actual
time=0.226..0.236 rows=6 loops=1)
Hash Cond: (s.datid = d.oid)
Buffers: shared hit=4
-> Function Scan on pg_stat_get_activity s (cost=0.00..1.00
rows=100 width=312) (actual time=0.148..0.151 rows=6 loop
-> Hash (cost=1.02..1.02 rows=2 width=68) (actual
time=0.034..0.034 rows=5 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 9kB
Buffers: shared hit=1
-> Seq Scan on pg_database d (cost=0.00..1.02 rows=2
width=68) (actual time=0.016..0.018 rows=5 loops=1)
Buffers: shared hit=1
-> Hash (cost=1.09..1.09 rows=9 width=68) (actual
time=0.015..0.015 rows=9 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 9kB
Buffers: shared hit=1
-> Seq Scan on pg_authid u (cost=0.00..1.09 rows=9
width=68) (actual time=0.004..0.008 rows=9 loops=1)
Buffers: shared hit=1
Planning Time: 1.902 ms
Buffers: shared hit=37 read=29
I/O Timings: read=0.506
Execution Time: 0.547 ms
(21 rows)

Note that there's a related discussion in the "Planning counters in
pg_stat_statements" thread, on whether to also compute buffers from
planning or not.