缓存：Redis

在 MySQL 中的大查询或 MongoDB 中的大聚合可能需要几秒甚至几分钟才能完成。你绝对不希望频繁地触发这些操作。

将查询或聚合结果缓存到内存中是缓解这个问题的绝佳方法。如果你的 API 服务器在单个机器或节点上运行，只需将这些结果放入内存中的 HashMaps 或 Dictionaries 中即可解决问题。 但是，如果你有多台机器或节点运行 API 服务器并共享其公共内存的话，则 Redis 才是你的最佳选择。

尝试 Redis

1. 在你的机器上安装 Redis 并启动它。

2. 添加 redis 依赖。

pip3 install redis

更新 requirements.txt:

pip3 freeze > requirements.txt

3. 更新代码。

添加 infrastructure/cache/helper.py:

from abc import ABC, abstractmethod


class CacheHelper(ABC):
    @abstractmethod
    def save(self, key: str, value: str) -> None:
        pass

    @abstractmethod
    def load(self, key: str) -> str:
        pass

使用 redis，infrastructure/cache/redis.py:

from typing import Any, Optional

from redis import Redis

from .helper import CacheHelper
from ..config import CacheConfig

DEFAULT_TTL = 3600


class RedisCache(CacheHelper):
    def __init__(self, c: CacheConfig):
        self.client = Redis(
            host=c.host,
            port=c.port,
            password=c.password,
            db=c.db,
        )

    def save(self, key: str, value: str) -> None:
        self.client.set(key, value, ex=DEFAULT_TTL)

    def load(self, key: str) -> Optional[str]:
        value: Any = self.client.get(key)
        if value is None:
            return None
        return value.decode("utf-8")

添加相关配置项，infrastructure/config/config.py:

@@ -14,6 +14,14 @@ class DBConfig:
     mongo_db_name: str
 
 
+@dataclass
+class CacheConfig:
+    host: str
+    port: int
+    password: str
+    db: int
+
+
 @dataclass
 class ApplicationConfig:
     port: int
@@ -22,6 +30,7 @@ class ApplicationConfig:
 @dataclass
 class Config:
     app: ApplicationConfig
+    cache: CacheConfig
     db: DBConfig
 
 
@@ -30,5 +39,6 @@ def parseConfig(filename: str) -> Config:
         data = yaml.safe_load(f)
         return Config(
             ApplicationConfig(**data['app']),
+            CacheConfig(**data['cache']),
             DBConfig(**data['db'])
         )

置入配置值，config.yml:

@@ -9,3 +9,8 @@ db:
   database: "lr_book"
   mongo_uri: "mongodb://localhost:27017"
   mongo_db_name: "lr_book"
+cache:
+  host: "localhost"
+  port: 6379
+  password: "test_pass"
+  db: 0

引入 redis 连接，application/wire_helper.py:

@@ -1,21 +1,27 @@
 from books.domain.gateway import BookManager, ReviewManager
+from books.infrastructure.cache import RedisCache, CacheHelper
 from ..infrastructure.config import Config
 from ..infrastructure.database import MySQLPersistence, MongoPersistence
 
 
 class WireHelper:
-    def __init__(self, sqlPersistence: MySQLPersistence, noSQLPersistence: MongoPersistence):
+    def __init__(self, sqlPersistence: MySQLPersistence, noSQLPersistence: MongoPersistence, kvStore: RedisCache):
         self.sqlPersistence = sqlPersistence
         self.noSQLPersistence = noSQLPersistence
+        self.kvStore = kvStore
 
     @classmethod
     def new(cls, c: Config):
         db = MySQLPersistence(c.db)
         mdb = MongoPersistence(c.db.mongo_uri, c.db.mongo_db_name)
-        return cls(db, mdb)
+        kv = RedisCache(c.cache)
+        return cls(db, mdb, kv)
 
     def book_manager(self) -> BookManager:
         return self.sqlPersistence
 
     def review_manager(self) -> ReviewManager:
         return self.noSQLPersistence
+
+    def cache_helper(self) -> CacheHelper:
+        return self.kvStore

假设列出所有图书操作需要在数据库中执行一个大查询，你需要将查询结果存入 Redis 以便下次可快速访问。

更改 application/executor/book_operator.py:

@@ -1,12 +1,19 @@
-from typing import List, Optional
+from dataclasses import asdict
+import json
+from typing import Any, Dict, List, Optional
+
+from books.infrastructure.cache.helper import CacheHelper
 from ...domain.model import Book
 from ...domain.gateway import BookManager
 
+BOOKS_KEY = "lr-books"
+
 
 class BookOperator():
 
-    def __init__(self, book_manager: BookManager):
+    def __init__(self, book_manager: BookManager, cache_helper: CacheHelper):
         self.book_manager = book_manager
+        self.cache_helper = cache_helper
 
     def create_book(self, b: Book) -> Book:
         id = self.book_manager.create_book(b)
@@ -17,7 +24,13 @@ class BookOperator():
         return self.book_manager.get_book(id)
 
     def get_books(self) -> List[Book]:
-        return self.book_manager.get_books()
+        v = self.cache_helper.load(BOOKS_KEY)
+        if v:
+            return json.loads(v)
+        books = self.book_manager.get_books()
+        self.cache_helper.save(
+            BOOKS_KEY, json.dumps([_convert(b) for b in books]))
+        return books
 
     def update_book(self, id: int, b: Book) -> Book:
         self.book_manager.update_book(id, b)
@@ -25,3 +38,10 @@ class BookOperator():
 
     def delete_book(self, id: int) -> None:
         return self.book_manager.delete_book(id)
+
+
+def _convert(b: Book) -> Dict[str, Any]:
+    new_b = asdict(b)
+    new_b['created_at'] = b.created_at.isoformat()
+    new_b['updated_at'] = b.updated_at.isoformat()
+    return new_b

微调 adapter/router.py:

@@ -108,7 +108,11 @@ def health():
 
 def make_router(app: Flask, wire_helper: WireHelper):
     rest_handler = RestHandler(
-        app.logger, BookOperator(wire_helper.book_manager()), ReviewOperator(wire_helper.review_manager()))
+        app.logger,
+        BookOperator(
+            wire_helper.book_manager(),
+            wire_helper.cache_helper()),
+        ReviewOperator(wire_helper.review_manager()))
     app.add_url_rule('/', view_func=health)
     app.add_url_rule('/books', view_func=rest_handler.get_books)
     app.add_url_rule('/books/<int:id>', view_func=rest_handler.get_book)

这些就是引入 redis 所需的调整。现在让我们试下缓存驱动的新端点。

用 curl 进行测试

列出所有图书：

curl -X GET -w "Total time: %{time_total}s\n" http://localhost:5000/books

结果与之前相似，但是性能显著提升。你可以通过 curl 的日志看出迹象。

Total time: 0.012821s
Total time: 0.008976s
Total time: 0.008859s
Total time: 0.008658s

使用 redis-cli 查看 Redis 中的值：

redis-cli

在 redis 客户端 shell 中调试这些键值：

127.0.0.1:6379> keys *
1) "lr-books"
127.0.0.1:6379> get lr-books
"[{\"id\":1,\"title\":\"Great Book II\",\"author\":\"Carl Smith\",\"published_at\":\"2022-01-01T08:00:00+08:00\",\"description\":\"Another sample book description\",\"isbn\":\"8334567890\",\"total_pages\":3880,\"created_at\":\"2024-02-25T16:29:31.353+08:00\",\"updated_at\":\"2024-02-25T16:29:31.353+08:00\"}]"
127.0.0.1:6379> del lr-books
(integer) 1

赞！Redis 已可以供君驱使了！💐