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Schema changes for application-level aggregation metrics. #3315

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Jul 22, 2024
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Schema changes for application-level aggregation metrics. #3315

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Schema changes for application-level aggregation metrics.
branlwyd Jul 22, 2024
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branlwyd Jul 22, 2024
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2 changes: 1 addition & 1 deletion aggregator_core/src/datastore.rs
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Expand Up @@ -102,7 +102,7 @@ macro_rules! supported_schema_versions {
// version is seen, [`Datastore::new`] fails.
//
// Note that the latest supported version must be first in the list.
supported_schema_versions!(6, 5);
supported_schema_versions!(7, 6);

/// Datastore represents a datastore for Janus, with support for transactional reads and writes.
/// In practice, Datastore instances are currently backed by a PostgreSQL database.
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1 change: 1 addition & 0 deletions db/00000000000007_task_aggregation_counters.down.sql
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@@ -0,0 +1 @@
DROP TABLE task_aggregation_counters;
14 changes: 14 additions & 0 deletions db/00000000000007_task_aggregation_counters.up.sql
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-- Per-task report aggregation counters, used for metrics.
--
-- Fillfactor is lowered to improve the likelihood of heap-only tuple optimizations. See the
-- discussion around this setting for the task_upload_counters table.
CREATE TABLE task_aggregation_counters(
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id BIGINT GENERATED ALWAYS AS IDENTITY PRIMARY KEY, -- artificial ID, internal only
task_id BIGINT NOT NULL, -- task ID the counter is associated with
ord BIGINT NOT NULL, -- the ordinal index of the task aggregation counter

success BIGINT NOT NULL DEFAULT 0, -- reports successfully aggregated

CONSTRAINT task_aggregation_counters_unique_id UNIQUE(task_id, ord),
CONSTRAINT fk_task_id FOREIGN KEY(task_id) REFERENCES tasks(id) ON DELETE CASCADE
) WITH (fillfactor = 50);
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Given that uploading these counter tables can be performance sensitive, I'm surprised we don't create an index on task ID. Maybe it's irrelevant because this table will be smallish anyway?

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CONSTRAINT task_aggregation_counters_unique_id UNIQUE(task_id, ord) implicitly creates an index on (task_id, ord). We only ever INSERT on (task_id, ord) or SELECT task_id and aggregate over ord.

I have some query plans from task upload counters #2508 (comment).

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UNIQUE constraints generate a (unique) index on the relevant fields, so we have an index on (task_id, ord).

See https://www.postgresql.org/docs/current/ddl-constraints.html#DDL-CONSTRAINTS-UNIQUE-CONSTRAINTS:

Adding a unique constraint will automatically create a unique B-tree index on the column or group of columns listed in the constraint.

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