Keep alive

[benbotto]

This PR allows the user to enable keep-alive on the underlying socket with a configurable initialDelay parameter, in milliseconds. Keep-alive is disabled by default. Example usage:

const pool = mysql.createPool({
  host: 'db',
  user: process.env.MYSQL_USER,
  password: process.env.MYSQL_PASSWORD,
  database: process.env.MYSQL_DATABASE,
  connectionLimit: 2,
  waitForConnections: true,
  queueLimit: 0,
  keepAliveInitialDelay: 10000, // 0 by default.
  enableKeepAlive: true, // false by default.
});

[sidorares]

I wonder if it worth making keepAlive on by default. If it won't add perf degradation and regression overall it'll potentially make life easier for many
At the same time default off is safer and we can change this behaviour later

[sidorares]

Also if it's default off and not mentioned in read me there is 0 chance it'll be used anywhere in prod

[benbotto]

It's up to you. I can update the PR if you want, but I wanted to err on the side of caution.

[benbotto]

There are some other issues that talk about ECONNRESET.

#897
#907
#128

In the first one the reporter is using Docker Swarm, so I'm pretty sure it's the same issue I was running up against.

At any rate, I wonder if there are some other members of the community that could test this change by enabling keep-alive manually using the new options in this PR. Then the option could be enabled by default if it's viewed as generally beneficial.

[sidorares]

Yeah, let's soft launch it first and I'll just advise all similar reports to try keepAlive option, later we can document and enable on by default

[midnightcodr]

@sidorares can you up the npm version so the enableKeepAlive and keepAliveInitialDelay options can be used? Thanks.

[sidorares]

after some thought - maybe .setKeepAlive() should have been added only when we create tcp/pipe connection instead of detecting if method is available on stream (after

node-mysql2/lib/connection.js

Line 39 in f9b9f96

}

line).

[benbotto]

I mentioned this as an aside over in #683, but I'm not up to speed on the four branches in the code referenced above (lines 31-45). There are 4 ways that this.stream gets set:

1. connecting over a unix socket;
2. connection via TCP;
3. a user-supplied stream;
4. or a factory function to produce a stream.

Is my understanding of (3) and (4) accurate? And in those cases, since the user is creating the stream, is it essentially up to them to enable keep-alive if they want to use it?

[sidorares]

@benbotto yes, all correct

[sidorares]

option 4 was added later when I realised that pool needs a way to know how to create new underlying connection and it was too late to remove option 3

[benbotto]

Cool, thanks for the clarification. I made the changed and added a new PR: #1086

[jsumners]

FYI: documentation should have been updated in this PR.

[DigitalSolomon]

Yeah, let's soft launch it first and I'll just advise all similar reports to try keepAlive option, later we can document and enable on by default

This deserves to be on the front page of the documentation. Took a lot of traveling down various rabbit holes to come upon this relatively simple solution. Would be great if this showed up on https://www.npmjs.com/package/mysql2 as well.

[Kennytian]

SET GLOBAL wait_timeout = 60;

run this command in mysql client command terminal, the timeout unit is seconds