连接池¶

Connection Pooling

中文

连接池是一种标准技术，用于在内存中维护长时间运行的连接以实现高效重用，并管理应用程序可能同时使用的总连接数。

特别是对于服务器端Web应用程序，连接池是维护内存中活动数据库连接“池(pool)”的标准方法，这些连接在请求之间重用。

SQLAlchemy包括几种连接池实现，它们与 Engine 集成。它们也可以直接用于希望为普通DBAPI方法添加池化的应用程序。

英文

A connection pool is a standard technique used to maintain long running connections in memory for efficient re-use, as well as to provide management for the total number of connections an application might use simultaneously.

Particularly for server-side web applications, a connection pool is the standard way to maintain a “pool” of active database connections in memory which are reused across requests.

SQLAlchemy includes several connection pool implementations which integrate with the Engine. They can also be used directly for applications that want to add pooling to an otherwise plain DBAPI approach.

连接池配置¶

Connection Pool Configuration

中文

create_engine() 函数返回的 Engine 在大多数情况下默认集成了 QueuePool，并且已经预先配置了合理的连接池默认值。如果你阅读本节只是为了了解如何启用连接池——恭喜你！你已经完成了。

最常用的 QueuePool 调优参数可以作为关键字参数直接传递给 create_engine()：包括 pool_size、 max_overflow、 pool_recycle 和 pool_timeout。例如:

engine = create_engine(
    "postgresql+psycopg2://me@localhost/mydb", pool_size=20, max_overflow=0
)

所有 SQLAlchemy 的连接池实现有一个共同点： 不会“预创建”连接 —— 所有实现都会在首次使用时才创建连接。在那一时刻，如果没有更多的并发连接请求，那么也不会创建更多的连接。因此，create_engine() 默认使用一个大小为 5 的 QueuePool 是完全可以接受的，而不需要考虑应用是否真的需要五个连接排队 —— 连接池只会在应用实际并发使用了五个连接时才增长到该大小，在这种情况下使用一个小型连接池是完全合理的默认行为。

备注

QueuePool 不兼容 asyncio。当使用 create_async_engine 创建 AsyncEngine 实例时，会使用 AsyncAdaptedQueuePool 类，该类基于 asyncio 兼容的队列实现。

英文

The Engine returned by the create_engine() function in most cases has a QueuePool integrated, pre-configured with reasonable pooling defaults. If you’re reading this section only to learn how to enable pooling - congratulations! You’re already done.

The most common QueuePool tuning parameters can be passed directly to create_engine() as keyword arguments: pool_size, max_overflow, pool_recycle and pool_timeout. For example:

engine = create_engine(
    "postgresql+psycopg2://me@localhost/mydb", pool_size=20, max_overflow=0
)

All SQLAlchemy pool implementations have in common that none of them “pre create” connections - all implementations wait until first use before creating a connection. At that point, if no additional concurrent checkout requests for more connections are made, no additional connections are created. This is why it’s perfectly fine for create_engine() to default to using a QueuePool of size five without regard to whether or not the application really needs five connections queued up - the pool would only grow to that size if the application actually used five connections concurrently, in which case the usage of a small pool is an entirely appropriate default behavior.

备注

The QueuePool class is not compatible with asyncio. When using create_async_engine to create an instance of AsyncEngine, the AsyncAdaptedQueuePool class, which makes use of an asyncio-compatible queue implementation, is used instead.

切换池实现¶

Switching Pool Implementations

中文

使用 create_engine() 使用其他类型的连接池的常规方法是使用 poolclass 参数。该参数接受从 sqlalchemy.pool 模块导入的类，并自动处理构建连接池的细节。一个常见的用例是禁用连接池，可以通过使用 NullPool 实现来实现该目标:

from sqlalchemy.pool import NullPool

engine = create_engine(
    "postgresql+psycopg2://scott:tiger@localhost/test", poolclass=NullPool
)

英文

The usual way to use a different kind of pool with create_engine() is to use the poolclass argument. This argument accepts a class imported from the sqlalchemy.pool module, and handles the details of building the pool for you. A common use case here is when connection pooling is to be disabled, which can be achieved by using the NullPool implementation:

from sqlalchemy.pool import NullPool

engine = create_engine(
    "postgresql+psycopg2://scott:tiger@localhost/test", poolclass=NullPool
)

使用自定义连接函数¶

Using a Custom Connection Function

中文

请参阅自定义 DBAPI connect() 参数/连接例程部分，了解各种连接定制例程的概述。

英文

See the section 自定义 DBAPI connect() 参数/连接例程 for a rundown of the various connection customization routines.

构建连接池¶

Constructing a Pool

中文

要单独使用 Pool，唯一必需的参数是 creator 函数，它作为第一个参数传入，其后可以附加其他选项:

import sqlalchemy.pool as pool
import psycopg2


def getconn():
    c = psycopg2.connect(user="ed", host="127.0.0.1", dbname="test")
    return c


mypool = pool.QueuePool(getconn, max_overflow=10, pool_size=5)

然后可以使用 Pool.connect() 方法从连接池中获取 DBAPI 连接。该方法返回一个 DBAPI 连接对象，但该对象被封装在一个透明代理中:

# 获取连接
conn = mypool.connect()

# 使用连接
cursor_obj = conn.cursor()
cursor_obj.execute("select foo")

该透明代理的目的是拦截 close() 调用，使其不会真正关闭 DBAPI 连接，而是将其归还给连接池:

# “关闭”连接 —— 实际上是将其归还给连接池
conn.close()

当代理对象被垃圾回收时，它也会将其内部的 DBAPI 连接归还给连接池，但由于 Python 中垃圾回收的非确定性（尽管在 cPython 中通常是及时的），因此不推荐依赖此行为；特别是在 asyncio DBAPI 驱动下，这种用法是不受支持的。

英文

To use a Pool by itself, the creator function is the only argument that’s required and is passed first, followed by any additional options:

import sqlalchemy.pool as pool
import psycopg2


def getconn():
    c = psycopg2.connect(user="ed", host="127.0.0.1", dbname="test")
    return c


mypool = pool.QueuePool(getconn, max_overflow=10, pool_size=5)

DBAPI connections can then be procured from the pool using the Pool.connect() function. The return value of this method is a DBAPI connection that’s contained within a transparent proxy:

# get a connection
conn = mypool.connect()

# use it
cursor_obj = conn.cursor()
cursor_obj.execute("select foo")

The purpose of the transparent proxy is to intercept the close() call, such that instead of the DBAPI connection being closed, it is returned to the pool:

# "close" the connection.  Returns
# it to the pool.
conn.close()

The proxy also returns its contained DBAPI connection to the pool when it is garbage collected, though it’s not deterministic in Python that this occurs immediately (though it is typical with cPython). This usage is not recommended however and in particular is not supported with asyncio DBAPI drivers.

返回时重置¶

Reset On Return

中文

该连接池实现包含了“返回时重置”行为 —— 在连接归还到连接池时会调用 DBAPI 连接的 rollback() 方法。这是为了清除连接上的任何事务状态，不仅包括未提交的数据，还包括表和行级别的锁。对大多数 DBAPI 而言，调用 rollback() 的开销很小；如果当前并没有活动事务，该方法通常是空操作（no-op）。

英文

The pool includes “reset on return” behavior which will call the rollback() method of the DBAPI connection when the connection is returned to the pool. This is so that any existing transactional state is removed from the connection, which includes not just uncommitted data but table and row locks as well. For most DBAPIs, the call to rollback() is inexpensive, and if the DBAPI has already completed a transaction, the method should be a no-op.

禁用非事务性连接的返回时重置¶

Disabling Reset on Return for non-transactional connections

中文

在某些特定场景下，这种 rollback() 行为可能是不必要的，例如当连接被配置为 autocommit 模式，或所使用的数据库引擎（如 MySQL 的 MyISAM 引擎）本身不具备 ACID 能力时。这种情况下通常出于性能考虑，会禁用返回时的重置行为。可以通过设置 Pool 的 Pool.reset_on_return 参数来实现禁用，也可以通过 create_engine() 的 create_engine.pool_reset_on_return 参数传入 None 值来设置。例如，结合 create_engine.isolation_level 参数设为 AUTOCOMMIT:

non_acid_engine = create_engine(
    "mysql://scott:tiger@host/db",
    pool_reset_on_return=None,
    isolation_level="AUTOCOMMIT",
)

上述 engine 在连接归还连接池时将不会执行 ROLLBACK；因为启用了 AUTOCOMMIT，驱动也不会执行 BEGIN 操作。

英文

For very specific cases where this rollback() is not useful, such as when using a connection that is configured for autocommit or when using a database that has no ACID capabilities such as the MyISAM engine of MySQL, the reset-on-return behavior can be disabled, which is typically done for performance reasons. This can be affected by using the Pool.reset_on_return parameter of Pool, which is also available from create_engine() as create_engine.pool_reset_on_return, passing a value of None. This is illustrated in the example below, in conjunction with the create_engine.isolation_level parameter setting of AUTOCOMMIT:

non_acid_engine = create_engine(
    "mysql://scott:tiger@host/db",
    pool_reset_on_return=None,
    isolation_level="AUTOCOMMIT",
)

The above engine won’t actually perform ROLLBACK when connections are returned to the pool; since AUTOCOMMIT is enabled, the driver will also not perform any BEGIN operation.

自定义返回时重置方案¶

Custom Reset-on-Return Schemes

中文

仅仅使用 rollback() 进行“重置”对于某些用例来说可能还不够充分；特别是对于使用临时表的应用，可能希望连接归还时自动清除这些临时表。部分（但并非所有）后端数据库提供了“重置”这些连接作用域资源的机制，这可能是连接池重置行为中所期望的功能。其他资源如 prepared statement 句柄、服务器端语句缓存等也可能在连接归还后继续存在，这取决于具体情况是否合适。某些后端（同样，并非全部）也可能提供相关的状态重置机制。SQLAlchemy 提供的 dialect 中，有两个已知支持此类重置机制的包括：

Microsoft SQL Server：有一个非官方但广为人知的存储过程 sp_reset_connection；
PostgreSQL：提供一组文档化良好的命令，如 DISCARD、RESET、DEALLOCATE 和 UNLISTEN。

备注

下一段及其示例应与 mssql/base.py 示例保持一致

下面的示例展示了如何使用 Microsoft SQL Server 的 sp_reset_connection 存储过程替换默认的“返回时重置”行为，通过 PoolEvents.reset() 事件钩子实现。我们将 create_engine.pool_reset_on_return 设置为 None，从而完全禁用默认行为，并由自定义方案取代。在实现中仍然调用了 .rollback()，以确保 DBAPI 内部的提交/回滚状态与事务状态保持一致:

from sqlalchemy import create_engine
from sqlalchemy import event

mssql_engine = create_engine(
    "mssql+pyodbc://scott:tiger^5HHH@mssql2017:1433/test?driver=ODBC+Driver+17+for+SQL+Server",
    # 禁用默认的“返回时重置”机制
    pool_reset_on_return=None,
)


@event.listens_for(mssql_engine, "reset")
def _reset_mssql(dbapi_connection, connection_record, reset_state):
    if not reset_state.terminate_only:
        dbapi_connection.execute("{call sys.sp_reset_connection}")

    # 保证 DBAPI 自身状态的一致性
    dbapi_connection.rollback()

在 2.0.0b3 版本发生变更: 为 PoolEvents.reset() 事件添加了更多状态参数，并确保该事件在所有“重置”场景中均被触发，使其成为自定义“重置”处理器的推荐位置。之前依赖 PoolEvents.checkin() 的方案仍然可用。

参见

连接池的临时表/资源重置 - 位于 Microsoft SQL Server 文档中
连接池的临时表/资源重置 - 位于 PostgreSQL 文档中

英文

“reset on return” consisting of a single rollback() may not be sufficient for some use cases; in particular, applications which make use of temporary tables may wish for these tables to be automatically removed on connection checkin. Some (but notably not all) backends include features that can “reset” such tables within the scope of a database connection, which may be a desirable behavior for connection pool reset. Other server resources such as prepared statement handles and server-side statement caches may persist beyond the checkin process, which may or may not be desirable, depending on specifics. Again, some (but again not all) backends may provide for a means of resetting this state. The two SQLAlchemy included dialects which are known to have such reset schemes include Microsoft SQL Server, where an undocumented but widely known stored procedure called sp_reset_connection is often used, and PostgreSQL, which has a well-documented series of commands including DISCARD RESET, DEALLOCATE, and UNLISTEN.

The following example illustrates how to replace reset on return with the Microsoft SQL Server sp_reset_connection stored procedure, using the PoolEvents.reset() event hook. The create_engine.pool_reset_on_return parameter is set to None so that the custom scheme can replace the default behavior completely. The custom hook implementation calls .rollback() in any case, as it’s usually important that the DBAPI’s own tracking of commit/rollback will remain consistent with the state of the transaction:

from sqlalchemy import create_engine
from sqlalchemy import event

mssql_engine = create_engine(
    "mssql+pyodbc://scott:tiger^5HHH@mssql2017:1433/test?driver=ODBC+Driver+17+for+SQL+Server",
    # disable default reset-on-return scheme
    pool_reset_on_return=None,
)


@event.listens_for(mssql_engine, "reset")
def _reset_mssql(dbapi_connection, connection_record, reset_state):
    if not reset_state.terminate_only:
        dbapi_connection.execute("{call sys.sp_reset_connection}")

    # so that the DBAPI itself knows that the connection has been
    # reset
    dbapi_connection.rollback()

在 2.0.0b3 版本发生变更: Added additional state arguments to the PoolEvents.reset() event and additionally ensured the event is invoked for all “reset” occurrences, so that it’s appropriate as a place for custom “reset” handlers. Previous schemes which use the PoolEvents.checkin() handler remain usable as well.

参见

连接池的临时表/资源重置 - in the Microsoft SQL Server documentation
连接池的临时表/资源重置 in the PostgreSQL documentation

记录返回时重置事件¶

Logging reset-on-return events

中文

连接池事件（包括“返回时重置”）的日志记录可以通过将 sqlalchemy.pool 记录器的日志级别设置为 logging.DEBUG 来启用，或者在使用 create_engine() 时，将 create_engine.echo_pool 参数设为 "debug" 来启用:

>>> from sqlalchemy import create_engine
>>> engine = create_engine("postgresql://scott:tiger@localhost/test", echo_pool="debug")

上述连接池将在日志中显示详细信息，包括“返回时重置”行为:

>>> c1 = engine.connect()
DEBUG sqlalchemy.pool.impl.QueuePool Created new connection <connection object ...>
DEBUG sqlalchemy.pool.impl.QueuePool Connection <connection object ...> checked out from pool
>>> c1.close()
DEBUG sqlalchemy.pool.impl.QueuePool Connection <connection object ...> being returned to pool
DEBUG sqlalchemy.pool.impl.QueuePool Connection <connection object ...> rollback-on-return

英文

Logging for pool events including reset on return can be set logging.DEBUG log level along with the sqlalchemy.pool logger, or by setting create_engine.echo_pool to "debug" when using create_engine():

>>> from sqlalchemy import create_engine
>>> engine = create_engine("postgresql://scott:tiger@localhost/test", echo_pool="debug")

The above pool will show verbose logging including reset on return:

>>> c1 = engine.connect()
DEBUG sqlalchemy.pool.impl.QueuePool Created new connection <connection object ...>
DEBUG sqlalchemy.pool.impl.QueuePool Connection <connection object ...> checked out from pool
>>> c1.close()
DEBUG sqlalchemy.pool.impl.QueuePool Connection <connection object ...> being returned to pool
DEBUG sqlalchemy.pool.impl.QueuePool Connection <connection object ...> rollback-on-return

池事件¶

Pool Events

中文

连接池支持一个事件接口，允许在首次连接、每次新建连接、以及连接的借出（checkout）与归还（checkin）时执行钩子操作。详见 PoolEvents。

英文

Connection pools support an event interface that allows hooks to execute upon first connect, upon each new connection, and upon checkout and checkin of connections. See PoolEvents for details.

使用 FIFO 与 LIFO¶

Using FIFO vs. LIFO

中文

QueuePool 类包含一个名为 QueuePool.use_lifo 的标志，也可以通过 create_engine() 函数的参数 create_engine.pool_use_lifo 进行设置。将此标志设为 True 会使连接池的“队列”行为改为“栈”行为，即最后归还到连接池的连接会是下一次请求中最先使用的。与连接池默认的先进先出（FIFO）行为相对，后进先出（LIFO）模式允许多余的连接在池中保持空闲，从而让服务器端的超时机制关闭这些连接。FIFO 与 LIFO 之间的区别，本质上在于是否希望连接池在空闲期间依然保持完整的连接集:

engine = create_engine("postgresql://", pool_use_lifo=True, pool_pre_ping=True)

上述示例中，我们还启用了 create_engine.pool_pre_ping 标志，以便连接池在服务器端关闭连接时能够优雅处理，并替换为新的连接。

请注意，该标志仅适用于 QueuePool。

参见

处理断开连接

英文

The QueuePool class features a flag called QueuePool.use_lifo, which can also be accessed from create_engine() via the flag create_engine.pool_use_lifo. Setting this flag to True causes the pool’s “queue” behavior to instead be that of a “stack”, e.g. the last connection to be returned to the pool is the first one to be used on the next request. In contrast to the pool’s long- standing behavior of first-in-first-out, which produces a round-robin effect of using each connection in the pool in series, lifo mode allows excess connections to remain idle in the pool, allowing server-side timeout schemes to close these connections out. The difference between FIFO and LIFO is basically whether or not its desirable for the pool to keep a full set of connections ready to go even during idle periods:

engine = create_engine("postgresql://", pool_use_lifo=True, pool_pre_ping=True)

Above, we also make use of the create_engine.pool_pre_ping flag so that connections which are closed from the server side are gracefully handled by the connection pool and replaced with a new connection.

Note that the flag only applies to QueuePool use.

参见

处理断开连接

使用具有多处理或 os.fork() 的连接池¶

Using Connection Pools with Multiprocessing or os.fork()

中文

当使用连接池（从而也包括通过 create_engine() 创建的 Engine）时， 务必不要将连接池共享给子进程 。TCP 连接由文件描述符表示，这些描述符通常能跨进程使用，这意味着可能会导致多个独立 Python 解释器状态同时访问同一个文件描述符。

根据驱动和操作系统的不同，可能出现的情况从连接无法使用到多个进程同时使用一个 socket 连接而导致的消息错乱（通常是最常见的情况）。

SQLAlchemy 的 Engine 对象引用的是一个已存在数据库连接的连接池。因此当该对象被复制到子进程时，目标是确保不会将任何数据库连接带入子进程。有以下四种通用方法可实现此目的：

使用 NullPool 禁用连接池。这是一种最简单的一次性机制，确保 Engine 创建的连接不会被重复使用:
```
from sqlalchemy.pool import NullPool

engine = create_engine("mysql+mysqldb://user:pass@host/dbname", poolclass=NullPool)
```

在子进程初始化阶段对任何给定的 Engine 调用 Engine.dispose()，并传入参数 Engine.dispose.close=False。这样可确保子进程不会触及父进程的连接，而是从新连接开始使用。 这是推荐方式:

from multiprocessing import Pool

engine = create_engine("mysql+mysqldb://user:pass@host/dbname")

def run_in_process(some_data_record):
    with engine.connect() as conn:
        conn.execute(text("..."))

def initializer():
    """确保子进程不会使用父进程的连接"""
    engine.dispose(close=False)

with Pool(10, initializer=initializer) as p:
    p.map(run_in_process, data)

在 1.4.33 版本加入: 添加了 Engine.dispose.close 参数，用于在子进程中替换连接池而不干扰父进程连接的使用。

在创建子进程之前直接调用 Engine.dispose()。这也能使子进程从新的连接池开始，同时确保父进程的连接不会被转移:

engine = create_engine("mysql://user:pass@host/dbname")


def run_in_process():
    with engine.connect() as conn:
        conn.execute(text("..."))


# 在进程启动前调用 dispose()
engine.dispose()
p = Process(target=run_in_process)
p.start()

可以为连接池添加事件处理器，用于检测连接是否被跨进程共享，并使其失效:

from sqlalchemy import event
from sqlalchemy import exc
import os

engine = create_engine("...")


@event.listens_for(engine, "connect")
def connect(dbapi_connection, connection_record):
    connection_record.info["pid"] = os.getpid()


@event.listens_for(engine, "checkout")
def checkout(dbapi_connection, connection_record, connection_proxy):
    pid = os.getpid()
    if connection_record.info["pid"] != pid:
        connection_record.dbapi_connection = connection_proxy.dbapi_connection = None
        raise exc.DisconnectionError(
            "连接记录属于进程 %s，"
            "当前尝试在进程 %s 中检出" % (connection_record.info["pid"], pid)
        )

上述方法中，我们采用了与断开连接处理 - 悲观中描述的方法类似的手段，将来源于其他父进程的 DBAPI 连接视为“无效”，强制连接池回收并创建新连接。

以上策略适用于 Engine 被多个进程共享的情况。对于跨进程共享某个特定 Connection 的情况，上述做法并不充分；应始终确保某个特定的 Connection 仅限于单个进程（和线程）使用。同样，不支持将任何处于事务状态的对象直接跨进程共享，例如已启动事务并持有活动 Connection 实例的 ORM Session 对象；在新进程中应创建新的 Session 实例。

英文

It’s critical that when using a connection pool, and by extension when using an Engine created via create_engine(), that the pooled connections are not shared to a forked process. TCP connections are represented as file descriptors, which usually work across process boundaries, meaning this will cause concurrent access to the file descriptor on behalf of two or more entirely independent Python interpreter states.

Depending on specifics of the driver and OS, the issues that arise here range from non-working connections to socket connections that are used by multiple processes concurrently, leading to broken messaging (the latter case is typically the most common).

The SQLAlchemy Engine object refers to a connection pool of existing database connections. So when this object is replicated to a child process, the goal is to ensure that no database connections are carried over. There are four general approaches to this:

Disable pooling using NullPool. This is the most simplistic, one shot system that prevents the Engine from using any connection more than once:
```
from sqlalchemy.pool import NullPool

engine = create_engine("mysql+mysqldb://user:pass@host/dbname", poolclass=NullPool)
```
Call Engine.dispose() on any given Engine, passing the Engine.dispose.close parameter with a value of False, within the initialize phase of the child process. This is so that the new process will not touch any of the parent process’ connections and will instead start with new connections. This is the recommended approach:
```
from multiprocessing import Pool

engine = create_engine("mysql+mysqldb://user:pass@host/dbname")


def run_in_process(some_data_record):
    with engine.connect() as conn:
        conn.execute(text("..."))


def initializer():
    """ensure the parent proc's database connections are not touched
    in the new connection pool"""
    engine.dispose(close=False)


with Pool(10, initializer=initializer) as p:
    p.map(run_in_process, data)
```
在 1.4.33 版本加入: Added the Engine.dispose.close parameter to allow the replacement of a connection pool in a child process without interfering with the connections used by the parent process.

Call Engine.dispose() directly before the child process is created. This will also cause the child process to start with a new connection pool, while ensuring the parent connections are not transferred to the child process:

engine = create_engine("mysql://user:pass@host/dbname")


def run_in_process():
    with engine.connect() as conn:
        conn.execute(text("..."))


# before process starts, ensure engine.dispose() is called
engine.dispose()
p = Process(target=run_in_process)
p.start()

An event handler can be applied to the connection pool that tests for connections being shared across process boundaries, and invalidates them:

from sqlalchemy import event
from sqlalchemy import exc
import os

engine = create_engine("...")


@event.listens_for(engine, "connect")
def connect(dbapi_connection, connection_record):
    connection_record.info["pid"] = os.getpid()


@event.listens_for(engine, "checkout")
def checkout(dbapi_connection, connection_record, connection_proxy):
    pid = os.getpid()
    if connection_record.info["pid"] != pid:
        connection_record.dbapi_connection = connection_proxy.dbapi_connection = None
        raise exc.DisconnectionError(
            "Connection record belongs to pid %s, "
            "attempting to check out in pid %s" % (connection_record.info["pid"], pid)
        )

Above, we use an approach similar to that described in 断开连接处理 - 悲观 to treat a DBAPI connection that originated in a different parent process as an “invalid” connection, coercing the pool to recycle the connection record to make a new connection.

The above strategies will accommodate the case of an Engine being shared among processes. The above steps alone are not sufficient for the case of sharing a specific Connection over a process boundary; prefer to keep the scope of a particular Connection local to a single process (and thread). It’s additionally not supported to share any kind of ongoing transactional state directly across a process boundary, such as an ORM Session object that’s begun a transaction and references active Connection instances; again prefer to create new Session objects in new processes.

直接使用连接池实例¶

Using a pool instance directly

中文

连接池实现可以在不使用 Engine 的情况下直接使用。这种方式适用于只希望使用连接池行为，而不需要 SQLAlchemy 其他功能的应用程序。

下面的示例中，通过 create_pool_from_url() 获取了 MySQLdb 方言的默认连接池:

from sqlalchemy import create_pool_from_url

my_pool = create_pool_from_url(
    "mysql+mysqldb://", max_overflow=5, pool_size=5, pre_ping=True
)

con = my_pool.connect()
# 使用连接
...
# 然后关闭它
con.close()

如果未显式指定要创建的连接池类型，将使用该方言的默认连接池类型。若希望明确指定连接池类型，可使用 poolclass 参数，如下示例所示:

from sqlalchemy import create_pool_from_url
from sqlalchemy import NullPool

my_pool = create_pool_from_url("mysql+mysqldb://", poolclass=NullPool)

英文

A pool implementation can be used directly without an engine. This could be used in applications that just wish to use the pool behavior without all other SQLAlchemy features. In the example below the default pool for the MySQLdb dialect is obtained using create_pool_from_url():

from sqlalchemy import create_pool_from_url

my_pool = create_pool_from_url(
    "mysql+mysqldb://", max_overflow=5, pool_size=5, pre_ping=True
)

con = my_pool.connect()
# use the connection
...
# then close it
con.close()

If the type of pool to create is not specified, the default one for the dialect will be used. To specify it directly the poolclass argument can be used, like in the following example:

from sqlalchemy import create_pool_from_url
from sqlalchemy import NullPool

my_pool = create_pool_from_url("mysql+mysqldb://", poolclass=NullPool)

API 文档 - 可用的连接池实现¶

API Documentation - Available Pool Implementations

Object Name	Description
_ConnectionFairy	Proxies a DBAPI connection and provides return-on-dereference support.
_ConnectionRecord	Maintains a position in a connection pool which references a pooled connection.
AssertionPool	A `Pool` that allows at most one checked out connection at any given time.
AsyncAdaptedQueuePool	An asyncio-compatible version of `QueuePool`.
ConnectionPoolEntry	Interface for the object that maintains an individual database connection on behalf of a `Pool` instance.
ManagesConnection	Common base for the two connection-management interfaces `PoolProxiedConnection` and `ConnectionPoolEntry`.
NullPool	A Pool which does not pool connections.
Pool	Abstract base class for connection pools.
PoolProxiedConnection	A connection-like adapter for a PEP 249 DBAPI connection, which includes additional methods specific to the `Pool` implementation.
QueuePool	A `Pool` that imposes a limit on the number of open connections.
SingletonThreadPool	A Pool that maintains one connection per thread.
StaticPool	A Pool of exactly one connection, used for all requests.

class sqlalchemy.pool.Pool¶

Abstract base class for connection pools.

Members

__init__(), connect(), dispose(), recreate(), status()

Class signature

class sqlalchemy.pool.Pool (sqlalchemy.log.Identified, sqlalchemy.event.registry.EventTarget)

method sqlalchemy.pool.Pool.__init__(creator: _CreatorFnType | _CreatorWRecFnType, recycle: int = -1, echo: log._EchoFlagType = None, logging_name: str | None = None, reset_on_return: _ResetStyleArgType = True, events: List[Tuple[_ListenerFnType, str]] | None = None, dialect: _ConnDialect | Dialect | None = None, pre_ping: bool = False, _dispatch: _DispatchCommon[Pool] | None = None)¶

Construct a Pool.

参数:

creator¶ – a callable function that returns a DB-API connection object. The function will be called with parameters.
recycle¶ – If set to a value other than -1, number of seconds between connection recycling, which means upon checkout, if this timeout is surpassed the connection will be closed and replaced with a newly opened connection. Defaults to -1.
logging_name¶ – String identifier which will be used within the “name” field of logging records generated within the “sqlalchemy.pool” logger. Defaults to a hexstring of the object’s id.
echo¶ –
if True, the connection pool will log informational output such as when connections are invalidated as well as when connections are recycled to the default log handler, which defaults to sys.stdout for output.. If set to the string "debug", the logging will include pool checkouts and checkins.

The Pool.echo parameter can also be set from the create_engine() call by using the create_engine.echo_pool parameter.

参见

配置日志记录 - further detail on how to configure logging.
reset_on_return¶ –
Determine steps to take on connections as they are returned to the pool, which were not otherwise handled by a Connection. Available from create_engine() via the create_engine.pool_reset_on_return parameter.

Pool.reset_on_return can have any of these values:
- "rollback" - call rollback() on the connection, to release locks and transaction resources. This is the default value. The vast majority of use cases should leave this value set.
- "commit" - call commit() on the connection, to release locks and transaction resources. A commit here may be desirable for databases that cache query plans if a commit is emitted, such as Microsoft SQL Server. However, this value is more dangerous than ‘rollback’ because any data changes present on the transaction are committed unconditionally.
- None - don’t do anything on the connection. This setting may be appropriate if the database / DBAPI works in pure “autocommit” mode at all times, or if a custom reset handler is established using the PoolEvents.reset() event handler.
- True - same as ‘rollback’, this is here for backwards compatibility.
- False - same as None, this is here for backwards compatibility.
For further customization of reset on return, the PoolEvents.reset() event hook may be used which can perform any connection activity desired on reset.

参见

返回时重置

PoolEvents.reset()
events¶ – a list of 2-tuples, each of the form (callable, target) which will be passed to listen() upon construction. Provided here so that event listeners can be assigned via create_engine() before dialect-level listeners are applied.
dialect¶ – a Dialect that will handle the job of calling rollback(), close(), or commit() on DBAPI connections. If omitted, a built-in “stub” dialect is used. Applications that make use of create_engine() should not use this parameter as it is handled by the engine creation strategy.
pre_ping¶ – if True, the pool will emit a “ping” (typically “SELECT 1”, but is dialect-specific) on the connection upon checkout, to test if the connection is alive or not. If not, the connection is transparently re-connected and upon success, all other pooled connections established prior to that timestamp are invalidated. Requires that a dialect is passed as well to interpret the disconnection error.

method sqlalchemy.pool.Pool.connect() → PoolProxiedConnection¶

Return a DBAPI connection from the pool.

The connection is instrumented such that when its close() method is called, the connection will be returned to the pool.

method sqlalchemy.pool.Pool.dispose() → None¶

Dispose of this pool.

This method leaves the possibility of checked-out connections remaining open, as it only affects connections that are idle in the pool.

参见

Pool.recreate()

method sqlalchemy.pool.Pool.recreate() → Pool¶

Return a new Pool, of the same class as this one and configured with identical creation arguments.

This method is used in conjunction with dispose() to close out an entire Pool and create a new one in its place.

method sqlalchemy.pool.Pool.status() → str¶: Returns a brief description of the state of this pool.

class sqlalchemy.pool.QueuePool¶

A Pool that imposes a limit on the number of open connections.

QueuePool is the default pooling implementation used for all Engine objects other than SQLite with a :memory: database.

The QueuePool class is not compatible with asyncio and create_async_engine(). The AsyncAdaptedQueuePool class is used automatically when using create_async_engine(), if no other kind of pool is specified.

参见

AsyncAdaptedQueuePool

Members

__init__(), dispose(), recreate(), status()

Class signature

class sqlalchemy.pool.QueuePool (sqlalchemy.pool.base.Pool)

method sqlalchemy.pool.QueuePool.__init__(creator: _CreatorFnType | _CreatorWRecFnType, pool_size: int = 5, max_overflow: int = 10, timeout: float = 30.0, use_lifo: bool = False, **kw: Any)¶

Construct a QueuePool.

参数:

creator¶ – a callable function that returns a DB-API connection object, same as that of Pool.creator.
pool_size¶ – The size of the pool to be maintained, defaults to 5. This is the largest number of connections that will be kept persistently in the pool. Note that the pool begins with no connections; once this number of connections is requested, that number of connections will remain. pool_size can be set to 0 to indicate no size limit; to disable pooling, use a NullPool instead.
max_overflow¶ – The maximum overflow size of the pool. When the number of checked-out connections reaches the size set in pool_size, additional connections will be returned up to this limit. When those additional connections are returned to the pool, they are disconnected and discarded. It follows then that the total number of simultaneous connections the pool will allow is pool_size + max_overflow, and the total number of “sleeping” connections the pool will allow is pool_size. max_overflow can be set to -1 to indicate no overflow limit; no limit will be placed on the total number of concurrent connections. Defaults to 10.
timeout¶ – The number of seconds to wait before giving up on returning a connection. Defaults to 30.0. This can be a float but is subject to the limitations of Python time functions which may not be reliable in the tens of milliseconds.
use_lifo¶ –
use LIFO (last-in-first-out) when retrieving connections instead of FIFO (first-in-first-out). Using LIFO, a server-side timeout scheme can reduce the number of connections used during non-peak periods of use. When planning for server-side timeouts, ensure that a recycle or pre-ping strategy is in use to gracefully handle stale connections.

参见

使用 FIFO 与 LIFO

处理断开连接
**kw¶ – Other keyword arguments including Pool.recycle, Pool.echo, Pool.reset_on_return and others are passed to the Pool constructor.

method sqlalchemy.pool.QueuePool.dispose() → None¶

Dispose of this pool.

This method leaves the possibility of checked-out connections remaining open, as it only affects connections that are idle in the pool.

参见

Pool.recreate()

method sqlalchemy.pool.QueuePool.recreate() → QueuePool¶

Return a new Pool, of the same class as this one and configured with identical creation arguments.

This method is used in conjunction with dispose() to close out an entire Pool and create a new one in its place.

method sqlalchemy.pool.QueuePool.status() → str¶: Returns a brief description of the state of this pool.

class sqlalchemy.pool.AsyncAdaptedQueuePool¶

An asyncio-compatible version of QueuePool.

This pool is used by default when using AsyncEngine engines that were generated from create_async_engine(). It uses an asyncio-compatible queue implementation that does not use threading.Lock.

The arguments and operation of AsyncAdaptedQueuePool are otherwise identical to that of QueuePool.

Class signature

class sqlalchemy.pool.AsyncAdaptedQueuePool (sqlalchemy.pool.impl.QueuePool)

class sqlalchemy.pool.SingletonThreadPool¶

A Pool that maintains one connection per thread.

Maintains one connection per each thread, never moving a connection to a thread other than the one which it was created in.

警告

the SingletonThreadPool will call .close() on arbitrary connections that exist beyond the size setting of pool_size, e.g. if more unique thread identities than what pool_size states are used. This cleanup is non-deterministic and not sensitive to whether or not the connections linked to those thread identities are currently in use.

SingletonThreadPool may be improved in a future release, however in its current status it is generally used only for test scenarios using a SQLite :memory: database and is not recommended for production use.

The SingletonThreadPool class is not compatible with asyncio and create_async_engine().

Options are the same as those of Pool, as well as:

参数:: pool_size¶ – The number of threads in which to maintain connections at once. Defaults to five.

SingletonThreadPool is used by the SQLite dialect automatically when a memory-based database is used. See SQLite.

Members

connect(), dispose(), recreate(), status()

Class signature

class sqlalchemy.pool.SingletonThreadPool (sqlalchemy.pool.base.Pool)

method sqlalchemy.pool.SingletonThreadPool.connect() → PoolProxiedConnection¶

Return a DBAPI connection from the pool.

The connection is instrumented such that when its close() method is called, the connection will be returned to the pool.

method sqlalchemy.pool.SingletonThreadPool.dispose() → None¶: Dispose of this pool.

method sqlalchemy.pool.SingletonThreadPool.recreate() → SingletonThreadPool¶

Return a new Pool, of the same class as this one and configured with identical creation arguments.

This method is used in conjunction with dispose() to close out an entire Pool and create a new one in its place.

method sqlalchemy.pool.SingletonThreadPool.status() → str¶: Returns a brief description of the state of this pool.

class sqlalchemy.pool.AssertionPool¶

A Pool that allows at most one checked out connection at any given time.

This will raise an exception if more than one connection is checked out at a time. Useful for debugging code that is using more connections than desired.

The AssertionPool class is compatible with asyncio and create_async_engine().

Members

dispose(), recreate(), status()

Class signature

class sqlalchemy.pool.AssertionPool (sqlalchemy.pool.base.Pool)

method sqlalchemy.pool.AssertionPool.dispose() → None¶

Dispose of this pool.

This method leaves the possibility of checked-out connections remaining open, as it only affects connections that are idle in the pool.

参见

Pool.recreate()

method sqlalchemy.pool.AssertionPool.recreate() → AssertionPool¶

Return a new Pool, of the same class as this one and configured with identical creation arguments.

This method is used in conjunction with dispose() to close out an entire Pool and create a new one in its place.

method sqlalchemy.pool.AssertionPool.status() → str¶: Returns a brief description of the state of this pool.

class sqlalchemy.pool.NullPool¶

A Pool which does not pool connections.

Instead it literally opens and closes the underlying DB-API connection per each connection open/close.

Reconnect-related functions such as recycle and connection invalidation are not supported by this Pool implementation, since no connections are held persistently.

The NullPool class is compatible with asyncio and create_async_engine().

Members

dispose(), recreate(), status()

Class signature

class sqlalchemy.pool.NullPool (sqlalchemy.pool.base.Pool)

method sqlalchemy.pool.NullPool.dispose() → None¶

Dispose of this pool.

This method leaves the possibility of checked-out connections remaining open, as it only affects connections that are idle in the pool.

参见

Pool.recreate()

method sqlalchemy.pool.NullPool.recreate() → NullPool¶

Return a new Pool, of the same class as this one and configured with identical creation arguments.

This method is used in conjunction with dispose() to close out an entire Pool and create a new one in its place.

method sqlalchemy.pool.NullPool.status() → str¶: Returns a brief description of the state of this pool.

class sqlalchemy.pool.StaticPool¶

A Pool of exactly one connection, used for all requests.

Reconnect-related functions such as recycle and connection invalidation (which is also used to support auto-reconnect) are only partially supported right now and may not yield good results.

The StaticPool class is compatible with asyncio and create_async_engine().

Members

dispose(), recreate(), status()

Class signature

class sqlalchemy.pool.StaticPool (sqlalchemy.pool.base.Pool)

method sqlalchemy.pool.StaticPool.dispose() → None¶

Dispose of this pool.

This method leaves the possibility of checked-out connections remaining open, as it only affects connections that are idle in the pool.

参见

Pool.recreate()

method sqlalchemy.pool.StaticPool.recreate() → StaticPool¶

Return a new Pool, of the same class as this one and configured with identical creation arguments.

This method is used in conjunction with dispose() to close out an entire Pool and create a new one in its place.

method sqlalchemy.pool.StaticPool.status() → str¶: Returns a brief description of the state of this pool.

class sqlalchemy.pool.ManagesConnection¶

Common base for the two connection-management interfaces PoolProxiedConnection and ConnectionPoolEntry.

These two objects are typically exposed in the public facing API via the connection pool event hooks, documented at PoolEvents.

Members

dbapi_connection, driver_connection, info, invalidate(), record_info

在 2.0 版本加入.

attribute sqlalchemy.pool.ManagesConnection.dbapi_connection: DBAPIConnection | None¶

A reference to the actual DBAPI connection being tracked.

This is a PEP 249-compliant object that for traditional sync-style dialects is provided by the third-party DBAPI implementation in use. For asyncio dialects, the implementation is typically an adapter object provided by the SQLAlchemy dialect itself; the underlying asyncio object is available via the ManagesConnection.driver_connection attribute.

SQLAlchemy’s interface for the DBAPI connection is based on the DBAPIConnection protocol object

参见

ManagesConnection.driver_connection

使用引擎时如何获取原始 DBAPI 连接？

attribute sqlalchemy.pool.ManagesConnection.driver_connection: Any | None¶

The “driver level” connection object as used by the Python DBAPI or database driver.

For traditional PEP 249 DBAPI implementations, this object will be the same object as that of ManagesConnection.dbapi_connection. For an asyncio database driver, this will be the ultimate “connection” object used by that driver, such as the asyncpg.Connection object which will not have standard pep-249 methods.

在 1.4.24 版本加入.

参见

ManagesConnection.dbapi_connection

使用引擎时如何获取原始 DBAPI 连接？

attribute sqlalchemy.pool.ManagesConnection.info¶

Info dictionary associated with the underlying DBAPI connection referred to by this ManagesConnection instance, allowing user-defined data to be associated with the connection.

The data in this dictionary is persistent for the lifespan of the DBAPI connection itself, including across pool checkins and checkouts. When the connection is invalidated and replaced with a new one, this dictionary is cleared.

For a PoolProxiedConnection instance that’s not associated with a ConnectionPoolEntry, such as if it were detached, the attribute returns a dictionary that is local to that ConnectionPoolEntry. Therefore the ManagesConnection.info attribute will always provide a Python dictionary.

参见

ManagesConnection.record_info

method sqlalchemy.pool.ManagesConnection.invalidate(e: BaseException | None = None, soft: bool = False) → None¶

Mark the managed connection as invalidated.

参数:

e¶ – an exception object indicating a reason for the invalidation.
soft¶ – if True, the connection isn’t closed; instead, this connection will be recycled on next checkout.

参见

更多关于失效的信息

attribute sqlalchemy.pool.ManagesConnection.record_info¶

Persistent info dictionary associated with this ManagesConnection.

Unlike the ManagesConnection.info dictionary, the lifespan of this dictionary is that of the ConnectionPoolEntry which owns it; therefore this dictionary will persist across reconnects and connection invalidation for a particular entry in the connection pool.

For a PoolProxiedConnection instance that’s not associated with a ConnectionPoolEntry, such as if it were detached, the attribute returns None. Contrast to the ManagesConnection.info dictionary which is never None.

参见

ManagesConnection.info

class sqlalchemy.pool.ConnectionPoolEntry¶

Interface for the object that maintains an individual database connection on behalf of a Pool instance.

The ConnectionPoolEntry object represents the long term maintainance of a particular connection for a pool, including expiring or invalidating that connection to have it replaced with a new one, which will continue to be maintained by that same ConnectionPoolEntry instance. Compared to PoolProxiedConnection, which is the short-term, per-checkout connection manager, this object lasts for the lifespan of a particular “slot” within a connection pool.

The ConnectionPoolEntry object is mostly visible to public-facing API code when it is delivered to connection pool event hooks, such as PoolEvents.connect() and PoolEvents.checkout().

在 2.0 版本加入: ConnectionPoolEntry provides the public facing interface for the _ConnectionRecord internal class.

Members

close(), dbapi_connection, driver_connection, in_use, info, invalidate(), record_info

Class signature

class sqlalchemy.pool.ConnectionPoolEntry (sqlalchemy.pool.base.ManagesConnection)

method sqlalchemy.pool.ConnectionPoolEntry.close() → None¶: Close the DBAPI connection managed by this connection pool entry.

attribute sqlalchemy.pool.ConnectionPoolEntry.dbapi_connection: DBAPIConnection | None¶

A reference to the actual DBAPI connection being tracked.

SQLAlchemy’s interface for the DBAPI connection is based on the DBAPIConnection protocol object

参见

ManagesConnection.driver_connection

使用引擎时如何获取原始 DBAPI 连接？

attribute sqlalchemy.pool.ConnectionPoolEntry.driver_connection: Any | None¶

The “driver level” connection object as used by the Python DBAPI or database driver.

在 1.4.24 版本加入.

参见

ManagesConnection.dbapi_connection

使用引擎时如何获取原始 DBAPI 连接？

attribute sqlalchemy.pool.ConnectionPoolEntry.in_use¶: Return True the connection is currently checked out

attribute sqlalchemy.pool.ConnectionPoolEntry.info¶

inherited from the ManagesConnection.info attribute of ManagesConnection

Info dictionary associated with the underlying DBAPI connection referred to by this ManagesConnection instance, allowing user-defined data to be associated with the connection.

参见

ManagesConnection.record_info

method sqlalchemy.pool.ConnectionPoolEntry.invalidate(e: BaseException | None = None, soft: bool = False) → None¶

inherited from the ManagesConnection.invalidate() method of ManagesConnection

Mark the managed connection as invalidated.

参数:

e¶ – an exception object indicating a reason for the invalidation.
soft¶ – if True, the connection isn’t closed; instead, this connection will be recycled on next checkout.

参见

更多关于失效的信息

attribute sqlalchemy.pool.ConnectionPoolEntry.record_info¶

inherited from the ManagesConnection.record_info attribute of ManagesConnection

Persistent info dictionary associated with this ManagesConnection.

参见

ManagesConnection.info

class sqlalchemy.pool.PoolProxiedConnection¶

A connection-like adapter for a PEP 249 DBAPI connection, which includes additional methods specific to the Pool implementation.

PoolProxiedConnection is the public-facing interface for the internal _ConnectionFairy implementation object; users familiar with _ConnectionFairy can consider this object to be equivalent.

在 2.0 版本加入: PoolProxiedConnection provides the public- facing interface for the _ConnectionFairy internal class.

Members

close(), dbapi_connection, detach(), driver_connection, info, invalidate(), is_detached, is_valid, record_info

Class signature

class sqlalchemy.pool.PoolProxiedConnection (sqlalchemy.pool.base.ManagesConnection)

method sqlalchemy.pool.PoolProxiedConnection.close() → None¶

Release this connection back to the pool.

The PoolProxiedConnection.close() method shadows the PEP 249 .close() method, altering its behavior to instead release the proxied connection back to the connection pool.

Upon release to the pool, whether the connection stays “opened” and pooled in the Python process, versus actually closed out and removed from the Python process, is based on the pool implementation in use and its configuration and current state.

attribute sqlalchemy.pool.PoolProxiedConnection.dbapi_connection: DBAPIConnection | None¶

A reference to the actual DBAPI connection being tracked.

SQLAlchemy’s interface for the DBAPI connection is based on the DBAPIConnection protocol object

参见

ManagesConnection.driver_connection

使用引擎时如何获取原始 DBAPI 连接？

method sqlalchemy.pool.PoolProxiedConnection.detach() → None¶

Separate this connection from its Pool.

This means that the connection will no longer be returned to the pool when closed, and will instead be literally closed. The associated ConnectionPoolEntry is de-associated from this DBAPI connection.

Note that any overall connection limiting constraints imposed by a Pool implementation may be violated after a detach, as the detached connection is removed from the pool’s knowledge and control.

attribute sqlalchemy.pool.PoolProxiedConnection.driver_connection: Any | None¶

The “driver level” connection object as used by the Python DBAPI or database driver.

在 1.4.24 版本加入.

参见

ManagesConnection.dbapi_connection

使用引擎时如何获取原始 DBAPI 连接？

attribute sqlalchemy.pool.PoolProxiedConnection.info¶

inherited from the ManagesConnection.info attribute of ManagesConnection

Info dictionary associated with the underlying DBAPI connection referred to by this ManagesConnection instance, allowing user-defined data to be associated with the connection.

参见

ManagesConnection.record_info

method sqlalchemy.pool.PoolProxiedConnection.invalidate(e: BaseException | None = None, soft: bool = False) → None¶

inherited from the ManagesConnection.invalidate() method of ManagesConnection

Mark the managed connection as invalidated.

参数:

e¶ – an exception object indicating a reason for the invalidation.
soft¶ – if True, the connection isn’t closed; instead, this connection will be recycled on next checkout.

参见

更多关于失效的信息

attribute sqlalchemy.pool.PoolProxiedConnection.is_detached¶: Return True if this PoolProxiedConnection is detached from its pool.

attribute sqlalchemy.pool.PoolProxiedConnection.is_valid¶: Return True if this PoolProxiedConnection still refers to an active DBAPI connection.

attribute sqlalchemy.pool.PoolProxiedConnection.record_info¶

inherited from the ManagesConnection.record_info attribute of ManagesConnection

Persistent info dictionary associated with this ManagesConnection.

参见

ManagesConnection.info

class sqlalchemy.pool._ConnectionFairy¶

Proxies a DBAPI connection and provides return-on-dereference support.

This is an internal object used by the Pool implementation to provide context management to a DBAPI connection delivered by that Pool. The public facing interface for this class is described by the PoolProxiedConnection class. See that class for public API details.

The name “fairy” is inspired by the fact that the _ConnectionFairy object’s lifespan is transitory, as it lasts only for the length of a specific DBAPI connection being checked out from the pool, and additionally that as a transparent proxy, it is mostly invisible.

参见

PoolProxiedConnection

ConnectionPoolEntry

Class signature

class sqlalchemy.pool._ConnectionFairy (sqlalchemy.pool.base.PoolProxiedConnection)

class sqlalchemy.pool._ConnectionRecord¶

Maintains a position in a connection pool which references a pooled connection.

This is an internal object used by the Pool implementation to provide context management to a DBAPI connection maintained by that Pool. The public facing interface for this class is described by the ConnectionPoolEntry class. See that class for public API details.

参见

ConnectionPoolEntry

PoolProxiedConnection

Class signature

class sqlalchemy.pool._ConnectionRecord (sqlalchemy.pool.base.ConnectionPoolEntry)

连接池¶

连接池配置¶

切换池实现¶

使用自定义连接函数¶

构建连接池¶

返回时重置¶

禁用非事务性连接的返回时重置¶

自定义返回时重置方案¶

记录返回时重置事件¶

池事件¶

处理断开连接¶

断开连接处理 - 悲观¶

自定义/旧式悲观 Ping¶

断开连接处理 - 乐观¶

设置池回收¶

更多关于失效的信息¶

支持断开连接场景的新数据库错误代码¶

使用 FIFO 与 LIFO¶

使用具有多处理或 os.fork() 的连接池¶

直接使用连接池实例¶

API 文档 - 可用的连接池实现¶