2016-10-10 17:31 GMT+02:00 Andrzej Zawadzki <zawadaa@xxxxx>:
Hi,
Today, I noticed strange situation:
The same query run on different servers has very different plan:
Q: SELECT b.* FROM kredytob b WHERE pesel = '22222222222' ORDER BY b.id DESC LIMIT 1
Slow plan:
"Limit (cost=0.43..28712.33 rows=1 width=4) (actual time=2574.041..2574.044 rows=1 loops=1)"
" Output: id"
" Buffers: shared hit=316132 read=110001"
" -> Index Scan Backward using kredytob_pkey on public.kredytob b (cost=0.43..3244444.80 rows=113 width=4) (actual time=2574.034..2574.034 rows=1 loops=1)"
" Output: id"
" Filter: (b.pesel = '22222222222'::bpchar)"
" Rows Removed by Filter: 433609"
here is backward index scan with - lot of rows is thrown
Rows Removed by Filter: 433609"
Rows Removed by Filter: 433609"
probably index definition on these servers are different
regards
Pavel
" Buffers: shared hit=316132 read=110001"
"Planning time: 0.414 ms"
"Execution time: 2574.139 ms"
Fast plan:
"Limit (cost=115240.66..115240.66 rows=1 width=4) (actual time=463.275..463.276 rows=1 loops=1)"
" Output: id"
" Buffers: shared hit=14661 read=4576"
" -> Sort (cost=115240.66..115240.94 rows=112 width=4) (actual time=463.271..463.271 rows=1 loops=1)"
" Output: id"
" Sort Key: b.id DESC"
" Sort Method: top-N heapsort Memory: 25kB"
" Buffers: shared hit=14661 read=4576"
" -> Index Scan using kredytob_pesel_typkred_opclass_idx on public.kredytob b (cost=0.43..115240.10 rows=112 width=4) (actual time=311.347..463.183 rows=5 loops=1)"
" Output: id"
" Index Cond: (b.pesel = '22222222222'::bpchar)"
" Buffers: shared hit=14661 read=4576"
"Planning time: 0.383 ms"
"Execution time: 463.324 ms"
Data is almost equal - "slow" has a few more rows in table. ("Fast" is a copy from 1 am today).
Why runtime is slower?
--
Andrzej Zawadzki
