JedisPool异常：Could not get a resource from the pool

JedisConnectionException: Could not get a resource from the pool  -------无法从连接池中获取到连接（资源）。

具体原因主要看Caused By子句。

下面Caused by可知，在调用borrowObject获取idle连接时，由于池中没有idle连接，出现阻塞等待，结果发生等待超时。

redis.clients.jedis.exceptions.JedisConnectionException: Could not get a resource from the pool
  …
Caused by: java.util.NoSuchElementException: Timeout waiting for idle object
at org.apache.commons.pool2.impl.GenericObjectPool.borrowObject(GenericObjectPool.java:449)

下面Caused by可知，同样在从池中获取idle连接时，由于池中没有idle连接，并且设置了不等待（blockWhenExhausted=false），故出现异常。

redis.clients.jedis.exceptions.JedisConnectionException: Could not get a resource from the pool
  …
Caused by: java.util.NoSuchElementException: Pool exhausted
at org.apache.commons.pool2.impl.GenericObjectPool.borrowObject(GenericObjectPool.java:464)

而我们的优付trans今天出现了如下Caused by的异常--- Pool not open。

2022-12-12 10:09:10.080 WARN  [clientBusiness_common_1670810950078S930,TID:d09088df43334542893d6ffc06399ff6.132.16708109500416701,0308d204b0a94d8eb6dd1b48ae72bcec] com.yft.opencommon.cache.JedisUtils:854 :getResource.
redis.clients.jedis.exceptions.JedisConnectionException: Could not get a resource from the pool
        at redis.clients.util.Pool.getResource(Pool.java:53)
        at redis.clients.jedis.JedisPool.getResource(JedisPool.java:226)
        at com.yft.opencommon.cache.JedisUtils.getResource(JedisUtils.java:851)
        at com.yft.opencommon.cache.JedisUtils.get(JedisUtils.java:53)
        at com.cn.yft.cache.RedisCacheUtil.getMerReqLimit(RedisCacheUtil.java:213)
        …
Caused by: java.lang.IllegalStateException: Pool not open
        at org.apache.commons.pool2.impl.BaseGenericObjectPool.assertOpen(BaseGenericObjectPool.java:759)
        at org.apache.commons.pool2.impl.GenericObjectPool.borrowObject(GenericObjectPool.java:395)
        at org.apache.commons.pool2.impl.GenericObjectPool.borrowObject(GenericObjectPool.java:346)
        at redis.clients.util.Pool.getResource(Pool.java:49)
        ... 76 common frames omitted

持续时间从上午10:09:10.080~10:17:00.306，影响部分客户下发。运营反馈后，立即重启服务暂时得到解决。

排查：

优付trans有4个节点做负载：两台在自建机房、两台在联通云机房。只有5号节点出现这个异常，其他节点未发现jedis异常。 

抛出Pool not open异常的源码在commons-pool2的BaseGenericObjectPool里

    /**
     * Verifies that the pool is open.
     * @throws IllegalStateException if the pool is closed.
     */
    final void assertOpen() throws IllegalStateException {
        if (isClosed()) {
            throw new IllegalStateException("Pool not open");
        }
    }

分析最大原因应该是连接问题， 即，redis服务器与5号节点通信出现不正常，导致JedisPool关闭了。日后继续详细分析。

关于Pool not open异常，网上这篇技术贴写的不错。JedisPool 在关闭情况下为什么 还能提供连接资源 并且 只有一个线程一直拿不到连接资源

微信公众号里也发现一篇文章，https://mp.weixin.qq.com/s/EWH-buDjBthxH6UGrFdP1w 列举jedis常见问题及redis缓存使用规范，值得读。