DB连接池是否有连接保活机制？

Q	A
Bug report?	yes
Feature request?	no
Swoft version	v2.0.11
Swoole version	4.4.8
PHP version	7.2.26 (cli)
Runtime environment	Docker

Describe the bug 最近应用日志频繁打印
SQLSTATE[HY000]: General error: 2006 MySQL server has gone away
导致http请求报错，影响业务。检查mysql错误日志发现有很多连接超时错误:
Aborted connection 220615606 to db: 'xxxxx' user: 'xxxxx' host: '172.31.3.176' (Got timeout reading communication packets) 初步怀疑是连接池内的连接长时间没有发起db请求，导致mysql服务端断开连接(wait_timeout/interactive_timeout均配置的3600)。swoft的db连接池是否没有定期向db发起保活请求？ Expected behavior

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Details

Describe what you are trying to achieve and what goes wrong.

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swoft-cloud / swoft

DB连接池是否有连接保活机制？ #1430