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JDBC Connection Query "select 1"

We have some webservices setup to hit Hadoop Impala's JDBC connection. We are seeing "select 1" queries every minute for each of the webservices that we have setup. Is there a way to change the frequency of these queries (they are being fired off every minute)? Also is it possible to have 1 of those queries executed instead of 14 seperate calls? Also can you explain what denodo is doing with these queries? Is it just to see if the destination is alive? Is it persisting the sessions? We are worried about resources in impala not releasing the resources for the queries being executed as we have seen some queries stuck in a "retrieved data but not closed" state.
07-03-2018 20:56:53 -0500

1 Answer

Hi, The queries you see are the test connection pings that you have enabled in the data source creation. Each connection retrieved from the connection pool will be validated by executing the ping query. This is the reason you are seeing the query executed every minute. Also, the ping query is a SQL query executed over the connections returned by the pool of connections to verify that the connection returned is still valid and not stale. The connections will only be validated if the field “Ping query” contains a query. Otherwise, they will not even if this check box is selected. It is best practice to have them enabled. To know more about test connections refer to the section ["JDBC Sources"]( of the Virtual DataPort Administration Guide. Hope this helps.
Denodo Team
09-03-2018 06:16:49 -0500
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