Optimize tag summary

[vithushau]

Addresses issue #686

Query

EXPLAIN (ANALYZE, BUFFERS) SELECT tagsyncstatus, COUNT(tagsyncstatus) as statuscount
FROM {tool_objectfs_objects}
GROUP BY tagsyncstatus

Before Index

QUERY PLAN
Limit (cost=9458.77..9509.44 rows=200 width=10) (actual time=25.231..27.320 rows=1 loops=1)
Buffers: shared hit=1166 read=4592
-> Finalize GroupAggregate (cost=9458.77..9509.44 rows=200 width=10) (actual time=25.230..27.319 rows=1 loops=1)
Group Key: tagsyncstatus
Buffers: shared hit=1166 read=4592
-> Gather Merge (cost=9458.77..9505.44 rows=400 width=10) (actual time=25.224..27.313 rows=3 loops=1)
Workers Planned: 2
Workers Launched: 2
Buffers: shared hit=1166 read=4592
-> Sort (cost=8458.74..8459.24 rows=200 width=10) (actual time=22.668..22.669 rows=1 loops=3)
Sort Key: tagsyncstatus
Sort Method: quicksort Memory: 25kB
Buffers: shared hit=1166 read=4592
Worker 0: Sort Method: quicksort Memory: 25kB
Worker 1: Sort Method: quicksort Memory: 25kB
-> Partial HashAggregate (cost=8449.10..8451.10 rows=200 width=10) (actual time=22.654..22.655 rows=1 loops=3)
Group Key: tagsyncstatus
Batches: 1 Memory Usage: 40kB
Buffers: shared hit=1152 read=4592
Worker 0: Batches: 1 Memory Usage: 40kB
Worker 1: Batches: 1 Memory Usage: 40kB
-> Parallel Seq Scan on mdl_tool_objectfs_objects (cost=0.00..7547.40 rows=180340 width=2) (actual time=0.018..11.493 rows=144272 loops=3)
Buffers: shared hit=1152 read=4592
Planning:
Buffers: shared hit=57
Planning Time: 0.120 ms
Execution Time: 27.342 ms

After Index

Limit (cost=1000.45..7469.80 rows=200 width=10) (actual time=15.054..16.905 rows=1 loops=1)
Buffers: shared hit=370
-> Finalize GroupAggregate (cost=1000.45..7469.80 rows=200 width=10) (actual time=15.053..16.904 rows=1 loops=1)
Group Key: tagsyncstatus
Buffers: shared hit=370
-> Gather Merge (cost=1000.45..7465.80 rows=400 width=10) (actual time=15.050..16.900 rows=3 loops=1)
Workers Planned: 2
Workers Launched: 2
Buffers: shared hit=370
-> Partial GroupAggregate (cost=0.42..6419.60 rows=200 width=10) (actual time=12.577..12.577 rows=1 loops=3)
Group Key: tagsyncstatus
Buffers: shared hit=370
-> Parallel Index Only Scan using mdl_toolobjeobje_tag_ix on mdl_tool_objectfs_objects (cost=0.42..5515.90 rows=180340 width=2) (actual time=0.023..6.061 rows=144272 loops=3)
Heap Fetches: 0
Buffers: shared hit=370
Planning:
Buffers: shared hit=71
Planning Time: 0.146 ms
Execution Time: 16.923 ms