8

我有一个使用 R管道工构建的 API，它使用RPostgreSQL和池连接到 PostgreSQL 数据库（尽管如果我使用的是 Shiny 应用程序，这也适用）：

# create the connection pool
pool <- dbPool(
  drv = PostgreSQL(),
  host = Sys.getenv("DB_HOST"),
  port = 5432,
  dbname = "db",
  user = Sys.getenv("DB_USER"),
  password = Sys.getenv("DB_PASSWORD")
)

# start the API
pr <- plumb("plumber.R")

# on stop, close the pool
pr$registerHooks(
  list("exit" = function() { poolClose(pool) })
)

我想每天导入新数据。最简单的方法是创建一个新数据库并将其推广到生产环境：

CREATE DATABASE db_new;
-- create the tables
-- bulk-insert the data
SELECT pg_terminate_backend (pid) FROM pg_stat_activity WHERE datname = 'db';
DROP DATABASE db;
ALTER DATABASE db_new RENAME TO db;

这是快速的，并且可以最大限度地减少停机时间。问题是pool然后失去与数据库的连接并且不会自动尝试重新连接：

> tbl(pool, "users")
Error in postgresqlExecStatement(conn, statement, ...) : 
  RS-DBI driver: (could not Retrieve the result : FATAL:  terminating connection due to administrator command
server closed the connection unexpectedly
    This probably means the server terminated abnormally
    before or while processing the request.
)

即使我不是每天都更换数据库，数据库服务器偶尔也会重新启动，这也会导致我的应用程序崩溃。重新连接似乎不是池、RPostgreSQL 或 DBI 的功能。有谁知道解决这个问题的方法？

4

2 回答 2

8

wait_timeout我最近遇到了类似的问题，因为当实例超出时 MySQL 连接被关闭。我在 RStudio Community 上看到了您的帖子，并受到您的解决方案的启发。如果您仍在使用它，并且正在寻找一种在包装您使用的实际函数时避免额外查询的解决方案，这里是一个演示我想出的东西的代表，以及一个证明它有效的示例：

library(dplyr, warn.conflicts = FALSE)
library(pool)
library(RMariaDB)

generate_safe_query <- function(pool) {
  function(db_function, ...) {
    tryCatch({
      db_function(pool, ...)
    }, error = function(e) {
      if (grepl("Lost connection to MySQL server during query", e$message)) {
        # Preserve `validationInterval` so that it can be restored
        validation_interval <- pool$validationInterval
        # Trigger destruction of dead connection
        pool$validationInterval <- 0
        refreshed_connection <- poolCheckout(pool)
        poolReturn(refreshed_connection)
        # Restore original `validationInterval`
        pool$validationInterval <- validation_interval
        # Execute the query with the new connection
        db_function(pool, ...)
      } else {
        # Unexpected error
        stop(e)
      }
    })
  }
}

mysql_pool <- dbPool(MariaDB(),
                     host = "127.0.0.1",
                     username = "root",
                     password = "",
                     dbname = "test")

safe_query <- generate_safe_query(mysql_pool)

# Works
safe_query(tbl, "notes")
#> # Source:   table<notes> [?? x 2]
#> # Database: mysql 8.0.15 [root@127.0.0.1:/test]
#>      id note 
#>   <int> <chr>
#> 1     1 NOTE1

# Set the `wait_timeout` to 5 seconds for this session
invisible(safe_query(dbExecute, "SET SESSION wait_timeout = 5"))

# Wait longer than `wait_timeout` to trigger a disconnect
Sys.sleep(6)

# Still works; warning will appear notifying that connection was
# destroyed and replaced with a new one
safe_query(tbl, "notes")
#> Warning: It wasn't possible to activate and/or validate the object. Trying
#> again with a new object.
#> # Source:   table<notes> [?? x 2]
#> # Database: mysql 8.0.15 [root@127.0.0.1:/test]
#>      id note 
#>   <int> <chr>
#> 1     1 NOTE1

safe_query(poolClose)
# Or, equivalently: 
# poolClose(mysql_pool)

由reprex 包（v0.3.0）于 2019 年 5 月 30 日创建

返回的函数generate_safe_query将适用于任何数据库查询函数（例如dbExecute、dbGetQuery等）。显然，您需要更新它匹配的错误消息以满足您的需要。

我还打开了我自己的社区主题，我认为应该包含一个选项dbPool，以减轻对此类变通办法的需求。

于 2019-05-30T21:59:13.320 回答
0

我正在使用具有以下功能的普通 DBI（无池）来始终为 DBI 调用提供活动连接（例如 DBI::dbExistsTable(rdsConnect(), "mytable")）。

#' Connect returns a database connection.
#' Retrieves the connection parameters from configuration.
#' 
#' FIXME: dbIsValid is not implemented
#' https://github.com/tomoakin/RPostgreSQL/issues/76
#' workaround implemented with isPostgresqlIdCurrent()
#' @return rds allocated connection
rdsConnect <- function() {
  if (!((exists("rds") && (isPostgresqlIdCurrent(rds))))) {
    source('./config.R', local = TRUE)
    print("New PostgreSQL connection")
    rds <<- DBI::dbConnect(RPostgreSQL::PostgreSQL(),
      dbname = rds_params("rds_database"),
      host = rds_params("rds_host"),
      user = rds_params("rds_user"),
      password = rds_params("rds_password")
    )
  } else print("Valid PostgreSQL connection")
  return(rds)
}
于 2020-02-01T07:00:04.580 回答