Am 29.08.2018 um 05:31 schrieb David:
For now, I can bypass the GIST index by avoiding range operators in my
queries. But why is the GIST index so slow?
your GiST-Index contains (member_id,group_id,valid_period), but your
query is only on the latter 2 fields.
test=*# create index test_index on member_span using gist
(group_id,valid_period);
CREATE INDEX
test=*# commit;
COMMIT
test=# explain analyse SELECT *
FROM app
JOIN group_span ON
app.group_id = group_span.group_id AND
app.app_time <@ group_span.valid_period
JOIN member_span ON
group_span.group_id = member_span.group_id AND
group_span.valid_period && member_span.valid_period;
QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------
Nested Loop (cost=319.27..776.18 rows=1 width=196) (actual
time=3.156..334.963 rows=10000 loops=1)
Join Filter: (app.group_id = member_span.group_id)
-> Hash Join (cost=319.00..771.00 rows=12 width=104) (actual
time=3.100..14.040 rows=10000 loops=1)
Hash Cond: (group_span.group_id = app.group_id)
Join Filter: (app.app_time <@ group_span.valid_period)
Rows Removed by Join Filter: 2000
-> Seq Scan on group_span (cost=0.00..257.00 rows=12000
width=59) (actual time=0.013..1.865 rows=12000 loops=1)
-> Hash (cost=194.00..194.00 rows=10000 width=45) (actual
time=3.037..3.037 rows=10000 loops=1)
Buckets: 16384 Batches: 1 Memory Usage: 910kB
-> Seq Scan on app (cost=0.00..194.00 rows=10000
width=45) (actual time=0.010..1.201 rows=10000 loops=1)
-> Index Scan using test_index on member_span (cost=0.28..0.42
rows=1 width=92) (actual time=0.027..0.031 rows=1 loops=10000)
Index Cond: ((group_id = group_span.group_id) AND
(group_span.valid_period && valid_period))
Planning time: 2.160 ms
Execution time: 335.820 ms
(14 rows)
test=*#
better?
Okay, other solution. The problem is the nested loop, we can disable that:
test=*# set enable_nestloop to false;
SET
test=*# explain analyse SELECT *
FROM app
JOIN group_span ON
app.group_id = group_span.group_id AND
app.app_time <@ group_span.valid_period
JOIN member_span ON
group_span.group_id = member_span.group_id AND
group_span.valid_period && member_span.valid_period;
QUERY PLAN
---------------------------------------------------------------------------------------------------------------------------------
Hash Join (cost=771.15..1121.33 rows=1 width=196) (actual
time=23.291..32.028 rows=10000 loops=1)
Hash Cond: (member_span.group_id = app.group_id)
Join Filter: (group_span.valid_period && member_span.valid_period)
Rows Removed by Join Filter: 2000
-> Seq Scan on member_span (cost=0.00..305.00 rows=12000 width=92)
(actual time=0.019..1.577 rows=12000 loops=1)
-> Hash (cost=771.00..771.00 rows=12 width=104) (actual
time=23.254..23.254 rows=10000 loops=1)
Buckets: 16384 (originally 1024) Batches: 1 (originally 1)
Memory Usage: 1486kB
-> Hash Join (cost=319.00..771.00 rows=12 width=104) (actual
time=7.968..18.951 rows=10000 loops=1)
Hash Cond: (group_span.group_id = app.group_id)
Join Filter: (app.app_time <@ group_span.valid_period)
Rows Removed by Join Filter: 2000
-> Seq Scan on group_span (cost=0.00..257.00
rows=12000 width=59) (actual time=0.010..2.068 rows=12000 loops=1)
-> Hash (cost=194.00..194.00 rows=10000 width=45)
(actual time=7.900..7.900 rows=10000 loops=1)
Buckets: 16384 Batches: 1 Memory Usage: 910kB
-> Seq Scan on app (cost=0.00..194.00 rows=10000
width=45) (actual time=0.011..3.165 rows=10000 loops=1)
Planning time: 1.241 ms
Execution time: 32.676 ms
(17 rows)
test=*#
Regards, Andreas
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