feat(ab-testing): add indexes to experiment-variant entity (#1223)

src/ab-testing/entities/experiment-variant.entity.ts

@@ -8,14 +8,46 @@ import {
   ManyToOne,
   OneToMany,
   VersionColumn,
+  Index,
 } from 'typeorm';
 import { Experiment } from './experiment.entity';
 import { VariantMetric } from './variant-metric.entity';
 
 /**
  * Represents the experiment Variant entity.
+ *
+ * ## Indexes (#1223)
+ *
+ * Every real query path against this entity loads variants through the
+ * `experiment` relation (`experimentRepository.findOne({ relations: [...] })`
+ * across `ab-testing.service.ts`, `experiments/experiment.service.ts`,
+ * `analysis/statistical-analysis.service.ts`,
+ * `automation/automated-decision.service.ts`, and
+ * `reporting/ab-testing-reports.service.ts`), then filters the loaded array
+ * in-memory for the control variant (`v.isControl`) or the winning variant
+ * (`v.isWinner`) — every one of those service methods does this. There is
+ * no direct `variantRepository.find({ where: ... })` call anywhere in this
+ * codebase filtering on anything else.
+ *
+ * The two composite indexes below match that access shape directly —
+ * `(experiment, isControl)` and `(experiment, isWinner)` — rather than a
+ * plain single-column index on `experiment` alone: leftmost-prefix lookup
+ * means either composite already serves a plain "all variants for this
+ * experiment" query just as well as a dedicated `experiment`-only index
+ * would, so adding one of those *in addition* would only be a redundant,
+ * un-selective duplicate (`isControl`/`isWinner` are booleans — indexing
+ * either alone, without the `experiment` prefix, has essentially no
+ * selectivity and no query in this codebase would use it that way).
+ *
+ * See `src/migrations/1802000000000-add-experiment-variant-indexes.ts` for
+ * the migration that creates the same two indexes on an existing database
+ * (`synchronize` is `false` in `src/config/datasource.ts`, so the
+ * `@Index` decorators below are the schema's documentation of intent, not
+ * what actually creates the indexes).
  */
 @Entity({ name: 'experiment_variants' })
+@Index(['experiment', 'isControl'])
+@Index(['experiment', 'isWinner'])
 export class IExperimentVariant {
   @PrimaryGeneratedColumn('uuid')
   id: string;

src/migrations/1802000000000-add-experiment-variant-indexes.ts

@@ -0,0 +1,35 @@
+import { MigrationInterface, QueryRunner } from 'typeorm';
+
+/**
+ * #1223 — src/ab-testing/entities/experiment-variant.entity.ts declared no
+ * indexes. Every real query path against `experiment_variants` loads
+ * variants through the `experiment` foreign key (via the `experiment`
+ * relation on `IExperimentVariant`, e.g.
+ * `experimentRepository.findOne({ relations: [...] })` across the
+ * ab-testing services), then filters in-memory for the control variant
+ * (`isControl`) or the winning variant (`isWinner`). These two composite
+ * indexes match that shape directly. See the `@Index` decorators and their
+ * accompanying comment on `IExperimentVariant` for the full rationale,
+ * including why this is two composites rather than three separate indexes
+ * (a plain `experimentId`-only index would be redundant given either
+ * composite already serves that lookup via its leftmost column).
+ */
+export class AddExperimentVariantIndexes1802000000000 implements MigrationInterface {
+  public async up(queryRunner: QueryRunner): Promise<void> {
+    await queryRunner.query(
+      'CREATE INDEX IF NOT EXISTS "IDX_experiment_variants_experiment_isControl" ON "experiment_variants" ("experimentId", "isControl")',
+    );
+    await queryRunner.query(
+      'CREATE INDEX IF NOT EXISTS "IDX_experiment_variants_experiment_isWinner" ON "experiment_variants" ("experimentId", "isWinner")',
+    );
+  }
+
+  public async down(queryRunner: QueryRunner): Promise<void> {
+    await queryRunner.query(
+      'DROP INDEX IF EXISTS "IDX_experiment_variants_experiment_isWinner"',
+    );
+    await queryRunner.query(
+      'DROP INDEX IF EXISTS "IDX_experiment_variants_experiment_isControl"',
+    );
+  }
+}