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b011869777
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.
18 lines
398 B
Python
18 lines
398 B
Python
# Generated by Django 3.2.6 on 2021-08-31 19:17
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from django.db import migrations
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class Migration(migrations.Migration):
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dependencies = [
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("zerver", "0342_realm_demo_organization_scheduled_deletion_date"),
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]
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operations = [
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migrations.AlterIndexTogether(
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name="useractivityinterval",
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index_together={("user_profile", "end")},
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),
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]
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