mysqlclient-pool

💡 About

This is a dynamic connection pool for mysqlclient connector and size of it grows as it requires. Extra connections will be terminated automatically if they're no longer needed.

The connection pool won't check the connectivity state of the connections before passing them to the user because in any time is still possible for the connection to drop in middle of the query. The user itself should watch for the disconnections.

The connection pool is thread-safe and can be shared on multithreaded context as long as the indivisual connection object not shared between the threads. However individual pool instances are required for different processes.

🔌 Installation

pip install mysqlclient-pool

📋 How to Use

Instantiating the connection pool. The pool also can be instantiated as a context manager using with statement.

from mysqlclient_pool import ConnectionPool
from MySQLdb._exceptions import OperationalError, ProgrammingError


try:
    pool = ConnectionPool(
        {
            "unix_socket": "/var/run/mysqld/mysqld.sock",
            "host": "localhost",
            "port": 3306,
            "user": "root",
            "password": "...",
            "database": "mysql"
        },
        size=20,
        timeout=10
    )
except TimeoutError:
    # Couldn't connect to the database server.
    # MySQL server service can be restarted in here if it's down.
    pass

Acquiring a cursor object from the pool. fetch() method commits or rollbacks the changes by default.

try:
    with pool.fetch() as cursor:
        cursor.execute("SELECT DATABASE()")
        print(cursor.fetchone())
except (OperationalError, ProgrammingError):
    # Handling MySQL errors
    pass
except pool.OverflowError:
    # The pool can't provide a connection anymore
    # because maximum permitted number of simultaneous
    # connections is exceeded.
    # `max_connections` variable of MySQL server configuration
    # can be tweaked to change the behaviour.
    pass
except pool.DrainedError:
    # The pool can't provide a connection anymore
    # because it can't access the database server.
    pass

connection object also can be accessed if needed. But any changes to connection should be reverted when returning the connection back to the pool.

with pool.fetch() as cursor:
    try:
      cursor.connection.autocommit(True)
      cursor.execute("INSERT INTO ...")
      cursor.execute("UPDATE ...")
      cursor.execute("DELETE FROM ...")
    finally:
      cursor.connection.autocommit(False)

Closing the pool when it's not needed anymore.

pool.close()

🔧 API

• class mysqlclient_pool.ConnectionPool

  • method __init__(config: dict, size: int = 10, timeout: int = 5, fillup: bool = True) -> None

    • parameter config:
      The keyword paramaters for creating the connection object.

    • parameter size:
      The minimum number of the connections in the pool.

    • parameter timeout:
      The time in seconds to wait for initiating the connection pool if the database server is unavailable.

    • parameter fillup:
      If True provided, fills up the connection pool up to the size parameter. Otherwise the connection pool is initially empty.

    • exception TimeoutError:
      When unable to fill up the connection pool due to inability to connect to the database server.

  • method close() -> None
    Closes the connection pool and disconnects all the connections.

  • method fetch(auto_manage: bool = True, cursor_type: MySQLdb.cursors.Cursor | MySQLdb.cursors.DictCursor = MySQLdb.cursors.Cursor) -> collections.abc.Generator[MySQLdb.cursors.Cursor | MySQLdb.cursors.DictCursor, None, None]
    Returns a cursor object from a dedicated connection.

    This is a context manager which pulls a connection from the pool and generates a cursor object from it and returns it to the user and at the end, if the connection hasn't disconnected in the way, closes the cursor and returns the connection back to the pool.

    • parameter auto_manage:
      If True provided, if no unhandled exception raised in the enclosed block, commits the current transaction upon completion of the block or rollbacks the transaction on an unhandled exception.

    • parameter cursor_type:
      Type of the cursor.

    • exception RuntimeError:
      When called after closing the connection pool.

    • exception ConnectionPool.DrainedError:
      When there's no connection available in the pool and unable to initiate new connections due to inability to connect to the database server.

    • exception ConnectionPool.OverflowError:
      When unable to initiate new connections due to maximum permitted number of simultaneous connections is exceeded.

  • property capacity: int
    The amount of idle connections present in the connection pool.

  • property closed: bool
    The state of the connection pool.