PooledDB 有这么几个参数
mincached : the initial number of idle connections in the pool (the default of 0 means no connections are made at startup)
maxcached: the maximum number of idle connections in the pool (the default value of 0 or None means unlimited pool size)
maxconnections: maximum number of connections generally allowed (the default value of 0 or None means any number of connections)
blocking: determines behavior when exceeding the maximum
其中 maxconnections 的描述有点奇怪，它说 generally allowed，为什么是 generally ？
设定 blocking=True，使用 MySQLdb 试验的结果如下：
1. 如果 maxconnections 参数不存在，那么连接数可以无限大，直至打满 mysql
2. 如果 maxcached < maxconnections，那么最大连接数就是 maxconnections, 但是奇怪的是，并不是所有 connections 都被复用了，pool 还是会创建新的连接
3. 如果 maxcached > maxconnections，那么最大连接数就是 maxcached, 同样存在 connections 可以复用但是还是会创建新连接的问题
测试代码
from threading import Thread
from DBUtils.PooledDB import PooledDB
from datetime import datetime
import MySQLdb pool = PooledDB(creator=MySQLdb,
mincached=1,
maxcached=3,
maxconnections=3,
blocking=True,
user="test",
passwd="test",
db="test") def test1(pool):
print("start: %s" % datetime.now())
conn = pool.connection()
print conn
cursor = conn.cursor()
print("select: %s" % datetime.now())
cursor.execute("select sleep(10)")
cursor.close()
conn.close()
print("end: %s" % datetime.now()) def main():
for i in xrange(15):
Thread(target=test1, args=(pool,)).start() if __name__ == "__main__":
main()