Elixir、Phoenix 和 Ecto：当数据库关闭时，提供缓存数据的请求变得非常缓慢从 100 毫秒到 3 秒

问题描述

我用--no-html和--database MysqL创建了一个凤凰项目

我们在工作中使用的版本是：

Erlang/OTP 21 [erts-10.2] [source] [64-bit] [smp:12:12] [ds:12:12:10] [async-threads:1] [hipe]

Elixir 1.8.0 (compiled with Erlang/OTP 20)

我正在做一个项目，作为状态页面工具 (hund.io) 和我们自己的 API 和报告工具之间的代理，所以我需要一个数据库来存储服务名称 + 请求的 url，并且，正如我需要一点点与数据库 Cachex (https://github.com/whitfin/cachex) 分离以将我的数据放入缓存

缓存数据时，使用邮递员请求我的包装器的 api 需要大约 100 毫秒才能获得响应，而 phoenix 的日志会显示类似 [info] Sent 200 in 1ms 但是，我曾经关闭过数据库，邮递员得到响应长达 3 秒，凤凰日志仍然说那种事情[info] Sent 200 in 1ms

我确信包装器在两种情况下都使用缓存数据：

我的代码：

def show(conn,%{"service_name" => service_name}) do
    Logger.debug("Top of show func")

    case Cachex.get(:proxies,service_name) do
      {:ok,nil} ->
        Logger.debug("Service #{service_name} not found in cache")
        proxy = Health.get_proxy_by_name!(service_name)
        Logger.debug("Service #{service_name} found in db")
        Cachex.put(:proxies,service_name,proxy)
        proxy_with_health = Checker.call_api(proxy)

        render(conn,"show.json",proxy_health: proxy_with_health)

      {:ok,proxy} ->
        Logger.debug("Found service #{service_name} in cache")
        proxy_with_health = Checker.call_api(proxy)
        render(conn,proxy_health: proxy_with_health)
    end
  end

日志：

[info] GET /api/proxies_health/docto
[debug] Processing with StatusWeb.ProxyHealthController.show/2
  Parameters: %{"service_name" => "docto"}
  Pipelines: [:api]
[debug] Top of show func
[debug] Found service docto in cache

对于路由器部分：

 pipeline :api do
    plug :accepts,["json"]
  end

  scope "/api",StatusWeb do
    pipe_through :api

    resources "/proxies",ProxyController,except: [:new,:edit]
    get "/proxies_health",ProxyHealthController,:index
    get "/proxies_health/:service_name",:show
  end

我还在日志中收到两个错误：

[error] MyXQL.Connection (#PID<0.373.0>) Failed to connect: ** (DBConnection.ConnectionError) connection refused

这看起来“正常”，因为应用程序想要重新连接到数据库而不断而这个，就在处理请求之前（至少根据日志）

[error] Could not create schema migrations table. This error usually happens due to the following:

  * The database does not exist
  * The "schema_migrations" table,which Ecto uses for managing
    migrations,was defined by another library
  * There is a deadlock while migrating (such as using concurrent
    indexes with a migration_lock)

To fix the first issue,run "mix ecto.create".

To address the second,you can run "mix ecto.drop" followed by
"mix ecto.create". Alternatively you may configure Ecto to use
another table and/or repository for managing migrations:

    config :status,Status.Repo,migration_source: "some_other_table_for_schema_migrations",migration_repo: AnotherRepoForSchemaMigrations

The full error report is shown below.

[error] GenServer #PID<0.620.0> terminating
** (DBConnection.ConnectionError) connection refused
    (db_connection) lib/db_connection/connection.ex:100: DBConnection.Connection.connect/2
    (connection) lib/connection.ex:622: Connection.enter_connect/5
    (stdlib) proc_lib.erl:249: :proc_lib.init_p_do_apply/3
Last message: nil
State: MyXQL.Connection

我试图在查看 How do I detect database connection issues from Elixir Ecto? 时放入我的 Status.Repo 文件 (repo.ex)

backoff_type: :stop

但它对我的问题没有任何改变

解决方法

作为我的代码，在缓存中找到对象的路径中（根本）不涉及数据库，我们最终发现问题来自端点中的插件，该插件应该只存在于开发环境 (MyAppWeb/endpoint.ex)

   if code_reloading? do
      plug Phoenix.CodeReloader
      plug Phoenix.Ecto.CheckRepoStatus,otp_app: :status
  end

这是一个插件，它会在每次请求时检查数据库是否已启动，是否已运行迁移等等待 Ecto 的答复，在 genserver 中超时意识到呼叫导致经历的延迟！

解决方法是简单地注释该行

          plug Phoenix.Ecto.CheckRepoStatus,otp_app: :status

ecto elixir elixir phoenix phoenix