**Transactions**

The application uses database transactions in several key operations:

- Invoice creation: When creating a new invoice, a transaction ensures that both the invoice and its items are created atomically
- Status updates: Invoice status changes are handled within transactions to maintain data consistency
- Client updates: When updating client information, related operations are wrapped in transactions

Transactions are implemented in the following files:

- `src/app/api/invoices/[id]/route.ts`: For updating and deleting invoices
- `src/app/api/invoices/route.ts`: For creating new invoices

**Triggers**

The system implements a sophisticated trigger system for invoice management:

- `invoice_status_update_trigger`: Automatically fires when an invoice status changes
  - Logs status changes in `InvoiceStatusHistory`
  - Creates notifications in `InvoiceNotifications`
  - Updates client status based on payment history
  - Automatically extends due dates when needed
  - Calculates and updates financial metrics

The trigger is implemented in `sql/01_invoice_status_trigger.sql`.

**Indexes**

Several optimized indexes are implemented for better query performance:

- Client email lookups:
  - `idx_client_email`: Basic email search optimization
  - `idx_client_email_tenant`: Composite index for tenant-specific email searches
  - `idx_client_email_lower`: Case-insensitive email searches
- Invoice management:
  - `idx_invoice_status_history_invoice_id`: Optimizes status history lookups
  - `idx_invoice_status_history_changed_at`: Improves date-based queries
  - `idx_invoice_notifications_invoice_id`: Speeds up notification retrieval
  - `idx_invoice_notifications_processed`: Partial index for unprocessed notifications


Using `EXPLAIN` on the `Client` table

  - Before creating the index:

{{{
EXPLAIN ANALYZE SELECT * FROM "Client" WHERE email = 'client12@example.com';
}}}

  - After adding index and creating 1000 rows:
{{{
EXPLAIN ANALYZE SELECT * FROM "Client" WHERE email = 'client12@example.com';
}}}

{{{
Index Scan using idx_client_email on "Client"  (cost=0.28..8.29 rows=1 width=303)
  Index Cond: (email = 'client12@example.com'::text)
}}}