issue fixing

[litrin]

Fixes #

Summary of changes:

• add 2 columns as public key and save time
• type int64 convert issue fixing.
• Close db connection when session closed.

How to verify it:

• check table structure
• connect to MySQL and exec: "show processlist;"

Testing done:

• version 0.15, Linux

[katarzyna-z]

Thanks for your contribution! 🐢

I see that tests fail, you need to use gofmt.

I suggest to divide your pull request into 3 pull requests, one pull requests for one thing.
It is also recommended to open 3 issues before these pull requests, to describe:

• why you need to add columns (please describe the use case)
• the issue with conversion
• the issue with closing of connection.

Our contributing guidelines could be helpful - CONTRIBUTING.md.

Regarding the closing of connection - I think that monitoring of connections could be added, something like it is in snap-plugin-publisher-influxdb, please see it.

If you need any help, please ask, we will try to cope with difficulties!