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Nodejs Sequelize is transparently doing this when ping connection.

That aside, I wonder why you need to keep the connection alive for > 30 mins, while usually sql con is short lived. Why can't you just close and reopen them, is it temporary table?

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Not the GP, but I assume transactional consistency was important for the report, hence the need to keep the connection alive. That's a pretty common situation.

Does it means the report take the tables hostage for 30+ minutes? How can transactional consistency be achieved without write lock? Temporary table?

MVCC.

Reporting can typically be split into two transactions. One long-running readonly transaction with snapshot consistency obtaining the data for the report and a separate transaction which publishes the result.

SQL connections can be arbitrarily long-lived. ETL processes and other data-intensive jobs often take multiple hours.

OP said it need to sleep for 30+ minutes. Is it common for connection to idle for half hours for etl processes?

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