fix: add missing indexes

Signed-off-by: Uroš Marolt <uros@marolt.me>

Author: themarolt

backend/src/database/migrations/U1774430554__covering-indexes-for-member-identity-lookups.sql

@@ -0,0 +1,36 @@
+-- Query: findMembersByVerifiedUsernames
+--
+-- Joins memberIdentities on (platform, lower(value)) with WHERE:
+--   verified = true AND type = 'username' AND deletedAt IS NULL
+--
+-- The existing idx_memberIdentities_platform_type_lower_value_memberId is
+-- missing verified = true in its partial condition, so PostgreSQL must
+-- heap-fetch every row to recheck verified, which is expensive when there
+-- are many unverified identities.
+--
+-- This index adds verified = true to the partial condition and includes memberId
+-- so the join to members can read memberId from the index without a heap fetch.
+CREATE INDEX CONCURRENTLY IF NOT EXISTS "idx_memberIdentities_verified_username_platform_lower_value"
+    ON "memberIdentities" (platform, lower(value), "memberId")
+    WHERE verified = true
+      AND type = 'username'
+      AND "deletedAt" IS NULL;
+
+-- Query: findMembersByVerifiedEmails
+--
+-- Joins memberIdentities on lower(value) with WHERE:
+--   verified = true AND type = 'email' AND deletedAt IS NULL
+--
+-- The existing idx_memberIdentities_verified_email_lower_value has the right
+-- partial condition but only stores lower(value) — no memberId. Every matched
+-- index entry requires a heap fetch to get memberId for the join to members.
+-- Under concurrent insert/update load, those heap fetches queue behind buffer
+-- pin locks, causing multi-second delays even for small inputs.
+--
+-- This index adds memberId so the join to members can proceed without
+-- touching the memberIdentities heap pages.
+CREATE INDEX CONCURRENTLY IF NOT EXISTS "idx_memberIdentities_verified_email_lower_value_memberid"
+    ON "memberIdentities" (lower(value), "memberId")
+    WHERE verified = true
+      AND type = 'email'
+      AND "deletedAt" IS NULL;