Black 23 enforces some slightly more specific rules about empty line
counts and redundant parenthesis removal, but the result is still
compatible with Black 22.
(This does not actually upgrade our Python environment to Black 23
yet.)
Signed-off-by: Anders Kaseorg <anders@zulip.com>
The `user_activity_interval` worker calls:
```python3
last = UserActivityInterval.objects.filter(user_profile=user_profile).order_by("-end")[0]
`````
Which results in a query like:
```sql
SELECT "zerver_useractivityinterval"."id", "zerver_useractivityinterval"."user_profile_id", "zerver_useractivityinterval"."start", "zerver_useractivityinterval"."end" FROM "zerver_useractivityinterval" WHERE "zerver_useractivityinterval"."user_profile_id" = 12345 ORDER BY "zerver_useractivityinterval"."end" DESC LIMIT 1
```
For users which have at least one matching row, this results in a
query plan like:
```
Limit (cost=0.56..711.38 rows=1 width=24) (actual time=0.078..0.078 rows=1 loops=1)
-> Index Scan Backward using zerver_useractivityinterval_7f021a14 on zerver_useractivityinterval (cost=0.56..1031399.46 rows=1451 width=24) (actual time=0.077..0.078 rows=1 loops=1)
Filter: (user_profile_id = 12345)
Rows Removed by Filter: 98
Planning Time: 0.059 ms
Execution Time: 0.088 ms
```
But for users that have just been created, with no matching rows, this
is considerably more expensive:
```
Limit (cost=0.56..711.38 rows=1 width=24) (actual time=10798.146..10798.146 rows=0 loops=1)
-> Index Scan Backward using zerver_useractivityinterval_7f021a14 on zerver_useractivityinterval (cost=0.56..1031399.46 rows=1451 width=24) (actual time=10798.145..10798.145 rows=0 loops=1)
Filter: (user_profile_id = 12345)
Rows Removed by Filter: (count of every single row in the table, redacted)
Planning Time: 0.053 ms
Execution Time: 10798.158 ms
```
Regular vacuuming can force the use of the index on `user_profile_id`
as long as there are few enough users, which is fast -- however, at
some point, the query planner decides that is insufficiently specific,
always chooses the effective-whole-table-scan.
Add an index on `(user_profile_id, end)`, which is expected to be
sufficiently specific that it is used even with large numbers of user
profiles.
Ref #19250.
Anders Kaseorg
Alex Vandiver