Add connectionLifetime to pool options

[dicearr]

This option is specially useful when connecting to serverless databases, in which the instances are turned off when there is no connection alive.

Fixes #1276

[dicearr]

Two tests are failing in one of the Travis jobs.

Node version: 6.16
DOCKER_MYSQL_TYPE=mariadb
DOCKER_MYSQL_VERSION=10.2

Files are:

test/unit/pool-cluster/test-connection-error-remove.js
test/unit/pool-cluster/test-connection-rr-error.js

I think those failures are unrelated to the changes but I am not hundred percent sure. The AppVeyor build for node v6.16 is passing.

[dougwilson]

Thank you. I will check out the CI failures 👍

[dolsup]

I think the timeout should be set every time after pool connection is released, not at the creation. and it have to be clear when pool connection is acquired again after release.

[dicearr]

That would be something like idleConnectionTimeout rather than connectionLifetime, right?

I have had time to check the PR again and you're completely right. In the way it is currently built if the connection expires while is being used the socket gets destroyed causing an error to be thrown. I think that unless I could gracefully close the connection, your suggestion is the way to go. Was that the reasoning behind your comment?

I have found #1749 which seems to be an attempt for implementing the idleConnectionTimeout, and #962 which is the related issue. The PR is stalled for no apparent reason.

@dougwilson Could you please share your thoughts about this? If the idleConnectionTimeout is the way to proceed I will close this PR and open a new one.

[dolsup]

@dicearr You said exactly what I meant.
In my case I made a monkey patch which is something like idleConnectionTimeout for my production which is built using microservice architecture and needs flexible pool size for each service. because the max connection capacity of my database is so small. I hope it goes to official feature.

And you can consult this PR.
sidorares/node-mysql2#736

[dicearr]

Closed in favor of #2218.