diff --git a/backend/models/subscription_models.py b/backend/models/subscription_models.py
index 996bc870..72dd66a2 100644
--- a/backend/models/subscription_models.py
+++ b/backend/models/subscription_models.py
@@ -6,7 +6,7 @@ Comprehensive models for usage-based subscription system with API cost tracking.
 # Ensure Optional is available in global scope for dynamic imports
 from typing import Optional
 
-from sqlalchemy import Column, Integer, String, DateTime, Float, Boolean, JSON, Text, ForeignKey, Enum
+from sqlalchemy import Column, Integer, String, DateTime, Float, Boolean, JSON, Text, ForeignKey, Enum, Index, UniqueConstraint
 from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy.orm import relationship
 from datetime import datetime, timedelta
@@ -174,6 +174,9 @@ class APIUsageLog(Base):
     
     # Indexes for performance
     __table_args__ = (
+        Index('ix_api_usage_logs_user_period_ts', 'user_id', 'billing_period', 'timestamp'),
+        Index('ix_api_usage_logs_user_provider_ts', 'user_id', 'provider', 'timestamp'),
+        Index('ix_api_usage_logs_user_status_ts', 'user_id', 'status_code', 'timestamp'),
         {'mysql_engine': 'InnoDB'},
     )
 
@@ -241,6 +244,8 @@ class UsageSummary(Base):
     
     # Unique constraint on user_id and billing_period
     __table_args__ = (
+        UniqueConstraint('user_id', 'billing_period', name='uq_usage_summaries_user_period'),
+        Index('ix_usage_summaries_user_period', 'user_id', 'billing_period'),
         {'mysql_engine': 'InnoDB'},
     )
 
@@ -276,6 +281,7 @@ class APIProviderPricing(Base):
     
     # Unique constraint on provider and model
     __table_args__ = (
+        UniqueConstraint('provider', 'model_name', name='uq_api_provider_pricing_provider_model'),
         {'mysql_engine': 'InnoDB'},
     )