Many sessions created by DVT custom query

[nehanene15]

Describe the bug
Customer is seeing a large number of sessions created for DVT commands on Redshift.
Some of them include:
'SELECT 1'
'COMMIT'
'ROLLBACK'
and multiple CREATE/DROP views for custom query.

What version of DVT are you using?
Latest

What type of connections are you using for source and target?
Redshift to BQ

Steps to reproduce the behavior
CX is running custom query column and row validations

Expected behavior
Creating/Dropping the view is necessary for extracting metadata from custom queries. We can justify those sessions, but reduce the others.

[nj1973]

Copying comment from PR to issue for visibility:

I'm not in favour of removing the pre ping for any other engines. I don't know enough about Redshift to understand why the customer sees the SELECT 1 queries as a threat.

It is interesting the issue reported is "Customer is seeing a large number of sessions created for DVT commands" because this was introduced as part of reducing the number of connections. We used to take a fresh connection for every validation but changed the code so that, if a DVT call needed to process 20 validations it would do them all in a single session. This had a knock on effect that sometimes sessions would "drop" (e.g. a firewall idle timeout) and then the whole DVT command would fail. By adding pre ping that dead session would be reconnected and the overall DVT would be able to continue.

Here is the PR for the change that added pre ping: #1320

[nj1973]

@nehanene15 , was this resolved by PR #1687?