https://community.cloudera.com/t5/Support-Questions/DBCP-connection-pool-issue-in-NIFI/m-p/290806#M215116 <P><a href="https://community.cloudera.com/t5/user/viewprofilepage/user-id/19178">@saivenkatg55</a>&nbsp;<BR /><BR />My first suggestion is that you always make sure you have configured the "validation query" property when using the DBCPConnectionPool controller service.<BR /><BR />When you enable the DBCPConnectionPool it does not immediately establish the configured number of connections for the pool.&nbsp; Upon receiving the first request from a processor for a connection from the DBCPConnectionPool, the entire pool will be created (by default configuration pool would consist of 8 connection).<BR /><BR />Subsequent requests by processor to for a connection results in one of the previously established connections being handed off to the requesting processor.&nbsp; If and only if the validation query is configured, the connection is first validated to make sure it is still good before being passed to requesting processor.&nbsp; So often times we see this issue when validation query is not set and the connections are no longer any good.&nbsp; Connections can go bad for many reasons (network issues, idle to long, etc...)<BR /><BR />You should keep your validation query very simple so it can execute very fast.&nbsp; "select 1" is often used to validate a connection.<BR /><BR />Also make sure you are using the latest version of NiFi.&nbsp; There have been numerous bug fixes around the processors and DBCPConnectionPool between Apache 1.0 and 1.11.<BR /><BR />Hope this helps,<BR />Matt</P> Mon, 02 Mar 2020 15:03:44 GMT MattWho 2020-03-02T15:03:44Z