Add index on aggregate_user (user_id, follower_count)

[stereosteve]

Most user list modals are sorted by follower_count desc. This index can save db from having to build full result set before doing pagination.

To take our "followers" query:

explain SELECT follower_user_id
from
follows
join users on users.user_id = follows.follower_user_id
join aggregate_user on follower_user_id = aggregate_user.user_id
where
follows.is_current = true
and follows.is_delete = false
and users.is_deactivated = false
and followee_user_id = 1
order by
follower_count desc,
aggregate_user.user_id asc
offset 0
limit 100;

Before:

 QUERY PLAN -------------------------------------------------------------------------------------------------------------------
Limit (cost=11168.09..11168.34 rows=100 width=16)
-> Sort (cost=11168.09..11170.18 rows=838 width=16)
Sort Key: aggregate_user.follower_count DESC, follows.follower_user_id
-> Nested Loop (cost=1.55..11136.06 rows=838 width=16)
-> Nested Loop (cost=1.12..10647.18 rows=838 width=8)
-> Index Scan using follows_inbound_idx on follows (cost=0.56..3418.39 rows=846 width=4)
Index Cond: ((followee_user_id = 1) AND (is_delete = false))
Filter: is_current
-> Index Scan using users_pkey on users (cost=0.56..8.53 rows=1 width=4)
Index Cond: (user_id = follows.follower_user_id)
Filter: (NOT is_deactivated)
-> Index Scan using aggregate_user_table_pkey on aggregate_user (cost=0.43..0.58 rows=1 width=12)
Index Cond: (user_id = users.user_id)
(13 rows)

After:

 QUERY PLAN --------------------------------------------------------------------------------------------------------------------------------------
Limit (cost=7837.26..7837.51 rows=100 width=16)
-> Sort (cost=7837.26..7839.36 rows=838 width=16)
Sort Key: aggregate_user.follower_count DESC, follows.follower_user_id
-> Nested Loop (cost=27.13..7805.24 rows=838 width=16)
Join Filter: (follows.follower_user_id = users.user_id)
-> Nested Loop (cost=26.57..6971.44 rows=846 width=16)
-> Bitmap Heap Scan on follows (cost=26.14..3328.85 rows=846 width=4)
Recheck Cond: (followee_user_id = 1)
Filter: (is_current AND (NOT is_delete))
-> Bitmap Index Scan on follows_inbound_idx (cost=0.00..25.93 rows=846 width=0)
Index Cond: ((followee_user_id = 1) AND (is_delete = false))
-> Index Only Scan using idx_aggregate_user_follower_count on aggregate_user (cost=0.43..4.31 rows=1 width=12)
Index Cond: (user_id = follows.follower_user_id)
-> Index Scan using users_pkey on users (cost=0.56..0.97 rows=1 width=4)
Index Cond: (user_id = aggregate_user.user_id)
Filter: (NOT is_deactivated)
(16 rows)

30% reduction in cost esitmate.

[changeset-bot]

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