Hi
I had to solve a slow due very slow JIT preparing. I found very unpleased situation where some subplan was strangely slow
-> Hash Anti Join (cost=11.35..19.41 rows=143 width=3011) (actual time=5039.022..5039.105 rows=203 loops=1)
Hash Cond: (term_p.id_i = term_d_1.id_i)
-> Seq Scan on public.term_p (cost=0.00..6.03 rows=203 width=24) (actual time=5038.980..5039.014 rows=203 loops=1)
Filter: (term_p.to_h IS NULL)
-> Hash (cost=10.60..10.60 rows=60 width=16) (actual time=0.008..0.009 rows=0 loops=1)
Buckets: 1024 Batches: 1 Memory Usage: 8kB
-> Seq Scan on public.term_d term_d_1 (cost=0.00..10.60 rows=60 width=16) (actual time=0.008..0.008 rows=0 loops=1)
It looks very strange - why does a scan of 203 rows need 5 sec?
There is a overhead of JIT but on different place of EXPLAIN
JIT:
Functions: 416
Options: Inlining true, Optimization true, Expressions true, Deforming true
Timing: Generation 61.002 ms, Inlining 67.897 ms, Optimization 2853.125 ms, Emission 2116.233 ms, Total 5098.258 ms
With some deduction we can detect so slow seq scan is probably JIT ??
But some tools like
https://explain.depesz.com displays very strange statistics then - so JIT overhead should be displayed in related plans too.
Regards
Pavel
