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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" " 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 |
