CAP定理的权衡实践：支付系统中的一致性优化与调优策略

用户下单 → 冻结余额 → 调用支付网关 → 修改订单状态 → 通知业务系统

# event_log.py
import uuid
from datetime import datetime
import sqlite3

def save_payment_event(user_id, order_id, amount):
    conn = sqlite3.connect('payment.db')
    cursor = conn.cursor()
    event_id = str(uuid.uuid4())
    cursor.execute("""
        INSERT INTO payment_events (event_id, user_id, order_id, amount, status, created_at)
        VALUES (?, ?, ?, ?, 'PENDING', ?)
    """, (event_id, user_id, order_id, amount, datetime.now()))
    conn.commit()
    conn.close()
    return event_id

# compensator.py
import time

def retry_failed_events():
    conn = sqlite3.connect('payment.db')
    cursor = conn.cursor()
    cursor.execute("""
        SELECT event_id, user_id, order_id, amount FROM payment_events
        WHERE status = 'PENDING'
    """)
    for event in cursor.fetchall():
        try:
            print(f"Retrying event {event[0]}")
            # 调用下游接口，例如支付网关
            result = process_payment(event[1], event[2], event[3])
            if result:
                cursor.execute("UPDATE payment_events SET status='SUCCESS' WHERE event_id=?", (event[0],))
        except:
            print(f"Event {event[0]} failed again.")
    conn.commit()
    conn.close()

def process_payment(user_id, order_id, amount):
    # 模拟调用支付网关
    print(f"Processing payment for user {user_id} - order {order_id}")
    return True

# 定时任务运行
if __name__ == "__main__":
    while True:
        retry_failed_events()
        time.sleep(30)  # 每 30 秒轮询一次

from jaeger_client import Config

def init_tracer(service):
    config = Config(
        config={
            'sampler': {'type': 'const', 'param': 1},
            'logging': True,
        },
        service_name=service,
    )
    return config.initialize_tracer()

# 使用 tracing
tracer = init_tracer("payment-service")

with tracer.start_span("freeze-balance") as span:
    span.set_tag("user_id", "u123")
    span.set_tag("amount", 100)
    # 调用账户服务

支付流程链路 Trace:
payment-service → account-service → gateway-service → order-service