Drop three route indexes no statement reads (#236)

* perf(db): drop three route indexes no statement reads

* docs(db): reword the retention residual comment

.github/workflows/ci.yml

@@ -58,7 +58,7 @@ jobs:
       - name: Verify stats and endpoint queries against PostgreSQL 16
         env:
           BEACON_TEST_POSTGRES_DSN: postgres://postgres:backup-ci-only@127.0.0.1:5432/postgres?sslmode=disable
-        run: go test ./db -run '^Test(Signal|Paths|PacketSummaries|PacketEndpointsResolveLive|ObserverMetrics|RouteEvidence|RouteEvidenceIndex|AnalyticsRetention|AnalyticsRetentionConcurrent|DeleteOldPacketsBatches|MeshMapperCatalogue|ChannelMessageScopes|NodeLocationReset|RunMigrations[A-Za-z]*|Reconfirm[A-Za-z]*|BigintCursors|RouteSearchHopOrder|StatsNodeTypesSplit|ListKnownRoutes|ListKnownRoutesMatchesLegacy|KnownRoutesCursorTies|KnownRoutesUnanalyzedRegion|KnownRoutesHopStatementsStayCustom|KnownRoutePaginationTies|RouteRetentionCutoffsExact|DeleteExpiredRoutes|DeleteGraceRoutesSlice|GraceWatermarkHeldByLockedRow)Postgres$' -count=1 -v
+        run: go test ./db -run '^Test(Signal|Paths|PacketSummaries|PacketEndpointsResolveLive|ObserverMetrics|RouteEvidence|RouteEvidenceIndex|AnalyticsRetention|AnalyticsRetentionConcurrent|DeleteOldPacketsBatches|MeshMapperCatalogue|ChannelMessageScopes|NodeLocationReset|RunMigrations[A-Za-z]*|KnownRoutesIndexSet|Reconfirm[A-Za-z]*|BigintCursors|RouteSearchHopOrder|StatsNodeTypesSplit|ListKnownRoutes|ListKnownRoutesMatchesLegacy|KnownRoutesCursorTies|KnownRoutesUnanalyzedRegion|KnownRoutesHopStatementsStayCustom|KnownRoutePaginationTies|RouteRetentionCutoffsExact|DeleteExpiredRoutes|DeleteGraceRoutesSlice|GraceWatermarkHeldByLockedRow)Postgres$' -count=1 -v
 
       - name: Verify route retention task against PostgreSQL 16
         env:

db/migrate_integration_test.go

@@ -180,3 +180,21 @@ func TestRunMigrationsHopIndexPrebuiltPostgres(t *testing.T) {
 		t.Fatalf("006 not recorded: %v", err)
 	}
 }
+
+// The migrations leave known_routes with exactly the indexes some statement reads, all usable.
+func TestKnownRoutesIndexSetPostgres(t *testing.T) {
+	ctx, pool := schemaPool(t)
+	if err := RunMigrations(ctx, pool); err != nil {
+		t.Fatal(err)
+	}
+	var got, bad []string
+	if err := pool.QueryRow(ctx, `SELECT coalesce(array_agg(indexrelid::regclass::text ORDER BY indexrelid::regclass::text), '{}'),
+       coalesce(array_agg(indexrelid::regclass::text) FILTER (WHERE NOT (indisvalid AND indisready)), '{}')
+FROM pg_index WHERE indrelid = 'known_routes'::regclass`).Scan(&got, &bad); err != nil {
+		t.Fatal(err)
+	}
+	want := []string{"idx_known_routes_hop_iata", "idx_known_routes_iata_keyset", "idx_known_routes_keyset", "idx_known_routes_node_ids", "known_routes_pkey"}
+	if strings.Join(got, ",") != strings.Join(want, ",") || len(bad) != 0 {
+		t.Fatalf("known_routes indexes = %v, want %v; not valid and ready: %v", got, want, bad)
+	}
+}

db/migrations/007_drop_known_routes_last_seen.sql

@@ -0,0 +1,5 @@
+-- Copyright 2026 Beacon Contributors
+-- SPDX-License-Identifier: AGPL-3.0-or-later
+
+-- No statement reads (last_seen DESC); retention walks idx_known_routes_keyset.
+DROP INDEX CONCURRENTLY IF EXISTS idx_known_routes_last_seen;

db/migrations/008_drop_known_routes_hop_count.sql

@@ -0,0 +1,5 @@
+-- Copyright 2026 Beacon Contributors
+-- SPDX-License-Identifier: AGPL-3.0-or-later
+
+-- No statement reads (iata, hop_count); hop filters use idx_known_routes_hop_iata.
+DROP INDEX CONCURRENTLY IF EXISTS idx_known_routes_hop_count;

db/migrations/009_drop_known_routes_reconfirm.sql

@@ -0,0 +1,5 @@
+-- Copyright 2026 Beacon Contributors
+-- SPDX-License-Identifier: AGPL-3.0-or-later
+
+-- No statement reads (last_reconfirmed_at); reconfirm no longer scans by it.
+DROP INDEX CONCURRENTLY IF EXISTS idx_known_routes_reconfirm;

db/queries/queries.sql

@@ -775,7 +775,8 @@ WHERE last_seen < $1
 -- name: DeleteExpiredRoutes :one
 -- One batch past retention, keyset after the per-run cursor (the first call passes -infinity, 0).
 -- The truncated bound (ms ceiling of the cutoff) drives idx_known_routes_keyset; the exact
--- residual decides membership. + interval 0 keeps it off idx_known_routes_last_seen.
+-- residual decides membership. + interval 0 keeps the exact cutoff a Filter, so the planner
+-- cannot switch to a last_seen index on deployments that still have one.
 WITH expired AS (
   SELECT r.iata, r.path_key, date_trunc('milliseconds', r.last_seen, 'UTC') AS ts, r.id
   FROM known_routes r

db/routes_statements_integration_test.go

@@ -82,7 +82,7 @@ func TestKnownRoutesCursorTiesPostgres(t *testing.T) {
 }
 
 // An unanalyzed region pages from iata_keyset, never a Sort over the region. Built on the
-// end-state index set (a later change drops the rest), where the (hop_count, iata) index must not win.
+// end-state index set (the baseline less what migrations 004-009 drop), where the (hop_count, iata) index must not win.
 func TestKnownRoutesUnanalyzedRegionPostgres(t *testing.T) {
 	ctx, tx := retentionTx(t)
 	applyBaseline(t, ctx, tx)

db/sqlc/querier.go

@@ -29,7 +29,8 @@ type Querier interface {
 	DeleteChannelMembersNotIn(ctx context.Context, arg DeleteChannelMembersNotInParams) error
 	// One batch past retention, keyset after the per-run cursor (the first call passes -infinity, 0).
 	// The truncated bound (ms ceiling of the cutoff) drives idx_known_routes_keyset; the exact
-	// residual decides membership. + interval 0 keeps it off idx_known_routes_last_seen.
+	// residual decides membership. + interval 0 keeps the exact cutoff a Filter, so the planner
+	// cannot switch to a last_seen index on deployments that still have one.
 	DeleteExpiredRoutes(ctx context.Context, arg DeleteExpiredRoutesParams) (DeleteExpiredRoutesRow, error)
 	// One batch of rarely-seen routes after the cursor, inside a window of at most 6 h below the grace
 	// cutoff: candidates without locks, then lock SKIP LOCKED through the pkey (re-checked on the newest

db/sqlc/queries.sql.go

@@ -195,7 +195,8 @@ type DeleteExpiredRoutesRow struct {
 
 // One batch past retention, keyset after the per-run cursor (the first call passes -infinity, 0).
 // The truncated bound (ms ceiling of the cutoff) drives idx_known_routes_keyset; the exact
-// residual decides membership. + interval 0 keeps it off idx_known_routes_last_seen.
+// residual decides membership. + interval 0 keeps the exact cutoff a Filter, so the planner
+// cannot switch to a last_seen index on deployments that still have one.
 func (q *Queries) DeleteExpiredRoutes(ctx context.Context, arg DeleteExpiredRoutesParams) (DeleteExpiredRoutesRow, error) {
 	row := q.db.QueryRow(ctx, deleteExpiredRoutes,
 		arg.AfterTs,