executor, server: reduce connect/disconnect log spam (#19308)

[ti-srebot]

cherry-pick #19308 to release-4.0

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What problem does this PR solve?

Issue Number: Part of #19053 (does not close issue)

Problem Summary:

Currently there is a lot of spam in the server error log related to client activity. This makes it hard to debug issues.

What is changed and how it works?

What's Changed:

This moves three Info log messages to be Debug messages instead:

• New sessions connecting to the server
• Sessions disconnecting from the server
• Setting session variables (global remains unchanged as Info)

This reduces the log spam in an oltp scenario (without a connection pool) quite considerably.

Related changes

• None

Check List

Tests

• Manual test (add detailed scripts or steps below)

I compiled the binary and ran while true; do mysql -e 'select 1'; sleep 1; done; in a loop. It looks much better.

Side effects

• Someone somewhere may rely on these log messages, and need to change their log file to debug. I think this is unlikely though.

Release note

• The TiDB error log now reports client connect/disconnect activity only under debug level verbosity.

[ti-srebot]

/run-all-tests

[ghost]

LGTM

[gregwebs]

From a security standpoint the information that there is a new connection could be very valuable and this might not be a minor change.

In a normal thread pool based usage it also wouldn't be that spammy.

[ghost]

In a normal thread pool based usage it also wouldn't be that spammy.

There are a lot of MySQL connectors that don't commonly use thread pools (PHP, perl, etc.) The information is still available under debug level.

[gregwebs]

The information is still available under debug level.

Yes, but imagine someone tries to audit a security problem based on their info logs after doing a minor version upgrade and discovers this information is no longer in the logs.

I 100% agree that the disconnect messages should be debug only. They would only be useful in an audit scenario if they showed something about the client identity as well.

[ti-srebot]

@ngaut, Thanks for your review, however we are sorry that your vote won't be count.

[winkyao]

/lgtm

[winkyao]

/merge

[ti-srebot]

/run-all-tests