Explain Code Execution and Bottlenecks

Motorola Solutions builds dispatch software for public safety radio networks. Here is a service class that pulls together data for a precinct's dispatch summary screen.

import sqlite3

class DispatchRecordService:
    def __init__(self, db_path):
        self.db_path = db_path

    def get_active_units(self, precinct_id):
        conn = sqlite3.connect(self.db_path)
        cursor = conn.cursor()
        cursor.execute("SELECT * FROM units WHERE precinct_id = ?", (precinct_id,))
        units = cursor.fetchall()
        conn.close()
        return units

    def get_recent_incidents(self, precinct_id):
        conn = sqlite3.connect(self.db_path)
        cursor = conn.cursor()
        cursor.execute("SELECT * FROM incidents WHERE precinct_id = ?", (precinct_id,))
        incidents = cursor.fetchall()
        conn.close()
        return incidents

    def build_dispatch_summary(self, precinct_id):
        units = self.get_active_units(precinct_id)
        summary = []
        for unit in units:
            unit_id = unit[0]
            conn = sqlite3.connect(self.db_path)
            cursor = conn.cursor()
            cursor.execute("SELECT * FROM assignments WHERE unit_id = ?", (unit_id,))
            assignments = cursor.fetchall()
            conn.close()
            summary.append({"unit": unit, "assignments": assignments})
        return summary

Explain what happens, step by step, when build_dispatch_summary is called for a busy precinct, and walk through the possible bottlenecks in this code. Then explain what you would change and why.