Re: using an index worst performances

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Tom Lane wrote:
| Gaetano Mendola <mendola(at)bigfoot(dot)com> writes:
|
|>Using a prepared query:
|
|
|>Without index and default stat 10 : 1.12 ms

ariadne=# explain analyze execute test_ariadne;
~ QUERY PLAN
- ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
~ Limit (cost=46.15..46.17 rows=1 width=760) (actual time=0.926..1.035 rows=3 loops=1)
~ -> Unique (cost=46.15..46.17 rows=1 width=760) (actual time=0.904..0.969 rows=3 loops=1)
~ -> Sort (cost=46.15..46.15 rows=1 width=760) (actual time=0.891..0.909 rows=3 loops=1)
~ Sort Key: store_nodes.parent, store_nodes.priority, store_nodes."path", store_objects.id, store_objects."type", store_objects.object, date_part('epoch'::text, store_objects.lastchanged), store_objects.vtype
~ -> Hash Join (cost=1.74..46.14 rows=1 width=760) (actual time=0.342..0.825 rows=3 loops=1)
~ Hash Cond: (("outer".vtype)::text = ("inner"."type")::text)
~ -> Nested Loop (cost=0.00..44.38 rows=1 width=760) (actual time=0.198..0.618 rows=3 loops=1)
~ -> Nested Loop (cost=0.00..38.93 rows=1 width=104) (actual time=0.157..0.447 rows=3 loops=1)
~ -> Seq Scan on store_prop_article (cost=0.00..1.75 rows=7 width=8) (actual time=0.030..0.119 rows=7 loops=1)
~ Filter: ((ar_start <= 1092924200) AND (ar_end >= 1092924200) AND ((ar_display)::text = 'default'::text))
~ -> Index Scan using store_nodes_object on store_nodes (cost=0.00..5.30 rows=1 width=96) (actual time=0.019..0.023 rows=0 loops=7)
~ Index Cond: ("outer".object = store_nodes.object)
~ Filter: (("path")::text ~~ '/sites/broadsat/news/%'::text)
~ -> Index Scan using store_objects_pkey on store_objects (cost=0.00..5.43 rows=1 width=672) (actual time=0.013..0.020 rows=1 loops=3)
~ Index Cond: ("outer".object = store_objects.id)
~ -> Hash (cost=1.74..1.74 rows=2 width=11) (actual time=0.085..0.085 rows=0 loops=1)
~ -> Seq Scan on store_types (cost=0.00..1.74 rows=2 width=11) (actual time=0.038..0.064 rows=1 loops=1)
~ Filter: ((implements)::text = 'particle'::text)
~ Total runtime: 1.199 ms
(19 rows)

|>Without index and default stat 1000 : 1.25 ms

ariadne=# explain analyze execute test_ariadne;
~ QUERY PLAN
- ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
~ Limit (cost=46.14..46.16 rows=1 width=760) (actual time=1.027..1.126 rows=3 loops=1)
~ -> Unique (cost=46.14..46.16 rows=1 width=760) (actual time=1.014..1.077 rows=3 loops=1)
~ -> Sort (cost=46.14..46.14 rows=1 width=760) (actual time=1.001..1.019 rows=3 loops=1)
~ Sort Key: store_nodes.parent, store_nodes.priority, store_nodes."path", store_objects.id, store_objects."type", store_objects.object, date_part('epoch'::text, store_objects.lastchanged), store_objects.vtype
~ -> Nested Loop (cost=0.00..46.13 rows=1 width=760) (actual time=0.278..0.933 rows=3 loops=1)
~ Join Filter: (("outer".vtype)::text = ("inner"."type")::text)
~ -> Nested Loop (cost=0.00..44.38 rows=1 width=760) (actual time=0.208..0.591 rows=3 loops=1)
~ -> Nested Loop (cost=0.00..38.93 rows=1 width=104) (actual time=0.168..0.417 rows=3 loops=1)
~ -> Seq Scan on store_prop_article (cost=0.00..1.75 rows=7 width=8) (actual time=0.038..0.118 rows=7 loops=1)
~ Filter: ((ar_start <= 1092924200) AND (ar_end >= 1092924200) AND ((ar_display)::text = 'default'::text))
~ -> Index Scan using store_nodes_object on store_nodes (cost=0.00..5.30 rows=1 width=96) (actual time=0.016..0.020 rows=0 loops=7)
~ Index Cond: ("outer".object = store_nodes.object)
~ Filter: (("path")::text ~~ '/sites/broadsat/news/%'::text)
~ -> Index Scan using store_objects_pkey on store_objects (cost=0.00..5.43 rows=1 width=672) (actual time=0.012..0.022 rows=1 loops=3)
~ Index Cond: ("outer".object = store_objects.id)
~ -> Seq Scan on store_types (cost=0.00..1.74 rows=1 width=11) (actual time=0.029..0.060 rows=1 loops=3)
~ Filter: ((implements)::text = 'particle'::text)
~ Total runtime: 1.288 ms
(18 rows)

|>With index and default stat 10: 1.35 ms

ariadne=# explain analyze execute test_ariadne;
~ QUERY PLAN
- ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
~ Limit (cost=14.95..14.97 rows=1 width=760) (actual time=1.066..1.165 rows=3 loops=1)
~ -> Unique (cost=14.95..14.97 rows=1 width=760) (actual time=1.052..1.116 rows=3 loops=1)
~ -> Sort (cost=14.95..14.95 rows=1 width=760) (actual time=1.036..1.054 rows=3 loops=1)
~ Sort Key: store_nodes.parent, store_nodes.priority, store_nodes."path", store_objects.id, store_objects."type", store_objects.object, date_part('epoch'::text, store_objects.lastchanged), store_objects.vtype
~ -> Hash Join (cost=3.51..14.94 rows=1 width=760) (actual time=0.614..0.968 rows=3 loops=1)
~ Hash Cond: ("outer".id = "inner".object)
~ -> Hash Join (cost=1.74..13.15 rows=1 width=768) (actual time=0.281..0.651 rows=5 loops=1)
~ Hash Cond: (("outer".vtype)::text = ("inner"."type")::text)
~ -> Nested Loop (cost=0.00..11.39 rows=1 width=768) (actual time=0.070..0.406 rows=6 loops=1)
~ -> Index Scan using test_index on store_nodes (cost=0.00..5.95 rows=1 width=96) (actual time=0.027..0.084 rows=6 loops=1)
~ Index Cond: ((("path")::text ~>=~ '/sites/broadsat/news/'::character varying) AND (("path")::text ~<~ '/sites/broadsat/news0'::character varying))
~ Filter: (("path")::text ~~ '/sites/broadsat/news/%'::text)
~ -> Index Scan using store_objects_pkey on store_objects (cost=0.00..5.43 rows=1 width=672) (actual time=0.012..0.020 rows=1 loops=6)
~ Index Cond: (store_objects.id = "outer".object)
~ -> Hash (cost=1.74..1.74 rows=2 width=11) (actual time=0.093..0.093 rows=0 loops=1)
~ -> Seq Scan on store_types (cost=0.00..1.74 rows=2 width=11) (actual time=0.029..0.054 rows=1 loops=1)
~ Filter: ((implements)::text = 'particle'::text)
~ -> Hash (cost=1.75..1.75 rows=7 width=8) (actual time=0.182..0.182 rows=0 loops=1)
~ -> Seq Scan on store_prop_article (cost=0.00..1.75 rows=7 width=8) (actual time=0.041..0.121 rows=7 loops=1)
~ Filter: ((ar_start <= 1092924200) AND (ar_end >= 1092924200) AND ((ar_display)::text = 'default'::text))
~ Total runtime: 1.358 ms
(21 rows)

|>With index and default stat 1000: 1.6 ms

ariadne=# explain analyze execute test_ariadne;
~ QUERY PLAN
- ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
~ Limit (cost=14.94..14.96 rows=1 width=760) (actual time=1.346..1.445 rows=3 loops=1)
~ -> Unique (cost=14.94..14.96 rows=1 width=760) (actual time=1.329..1.393 rows=3 loops=1)
~ -> Sort (cost=14.94..14.94 rows=1 width=760) (actual time=1.317..1.335 rows=3 loops=1)
~ Sort Key: store_nodes.parent, store_nodes.priority, store_nodes."path", store_objects.id, store_objects."type", store_objects.object, date_part('epoch'::text, store_objects.lastchanged), store_objects.vtype
~ -> Hash Join (cost=1.77..14.93 rows=1 width=760) (actual time=0.663..1.249 rows=3 loops=1)
~ Hash Cond: ("outer".id = "inner".object)
~ -> Nested Loop (cost=0.00..13.14 rows=1 width=768) (actual time=0.268..0.936 rows=5 loops=1)
~ Join Filter: (("outer".vtype)::text = ("inner"."type")::text)
~ -> Nested Loop (cost=0.00..11.39 rows=1 width=768) (actual time=0.070..0.412 rows=6 loops=1)
~ -> Index Scan using test_index on store_nodes (cost=0.00..5.95 rows=1 width=96) (actual time=0.027..0.093 rows=6 loops=1)
~ Index Cond: ((("path")::text ~>=~ '/sites/broadsat/news/'::character varying) AND (("path")::text ~<~ '/sites/broadsat/news0'::character varying))
~ Filter: (("path")::text ~~ '/sites/broadsat/news/%'::text)
~ -> Index Scan using store_objects_pkey on store_objects (cost=0.00..5.43 rows=1 width=672) (actual time=0.013..0.020 rows=1 loops=6)
~ Index Cond: (store_objects.id = "outer".object)
~ -> Seq Scan on store_types (cost=0.00..1.74 rows=1 width=11) (actual time=0.025..0.051 rows=1 loops=6)
~ Filter: ((implements)::text = 'particle'::text)
~ -> Hash (cost=1.75..1.75 rows=7 width=8) (actual time=0.181..0.181 rows=0 loops=1)
~ -> Seq Scan on store_prop_article (cost=0.00..1.75 rows=7 width=8) (actual time=0.040..0.122 rows=7 loops=1)
~ Filter: ((ar_start <= 1092924200) AND (ar_end >= 1092924200) AND ((ar_display)::text = 'default'::text))
~ Total runtime: 1.616 ms
(20 rows)

| Could we see EXPLAIN ANALYZE EXECUTE output for each case?
|

See above.

BTW I dont know if this is a known issue:

After the prepare statement:

ariadne=# drop index test_index;
DROP INDEX
ariadne=# explain analyze execute test_ariadne;
ERROR: could not open relation with OID 53695

Regards
Gaetano Mendola

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