fix(db): add partial index to optimize object lookup queries

pkg/db/migration/000058_add_object_uid_partial_index.down.sql

@@ -0,0 +1 @@
+DROP INDEX IF EXISTS idx_object_uid_not_deleted;

pkg/db/migration/000058_add_object_uid_partial_index.up.sql

@@ -0,0 +1,17 @@
+-- ============================================================================
+-- Migration: Add partial index on object(uid) for soft-delete queries
+-- ============================================================================
+-- This migration adds a partial index to optimize queries like:
+--   SELECT ... FROM object WHERE uid = '...' AND delete_time IS NULL
+--
+-- The primary key on uid doesn't include delete_time, so the query planner
+-- must perform a filter step after the index scan. Under high concurrency
+-- (e.g., many simultaneous file uploads), this causes slow queries (200-400ms).
+--
+-- A partial index allows direct lookups without filtering.
+-- ============================================================================
+-- Note: Not using CONCURRENTLY as it cannot run in a transaction,
+-- and most migration frameworks require transaction support.
+CREATE INDEX IF NOT EXISTS idx_object_uid_not_deleted ON object(uid)
+WHERE delete_time IS NULL;
+COMMENT ON INDEX idx_object_uid_not_deleted IS 'Partial index for efficient lookup of non-deleted objects by uid';

pkg/db/migration/migration.go

@@ -9,7 +9,7 @@ import (
 )
 
 // TargetSchemaVersion determines the database schema version.
-const TargetSchemaVersion uint = 57
+const TargetSchemaVersion uint = 58
 
 type migration interface {
 	Migrate() error