*: Change default for unix socket

[morgo]

What problem does this PR solve?

Issue Number: close #28484

Problem Summary:

In #28482 it is proposed that the security be improved by using AuthSocket.

This only makes sense when socket listening is enabled by default.

What is changed and how it works?

What's Changed:

As well as listening on TCP:4000, the tidb-server now listens on a unix socket at /tmp/tidb.sock by default.

Check List

Tests

• Unit test
  We actually have great existing tests for this (checking if the config file differs by defaults, and socket listening in the server package).
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

As well as listening on `TCP:4000`, the tidb-server now listens on a unix socket at `/tmp/tidb.sock` by default.

[ti-chi-bot]

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This pull request has been approved by:

• dveeden
• mjonss

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[dveeden]

1. I think this is fine since tidb using unix socket cannot restart if after SIGKILL #26058 is fixed. If this PR needs to be backported to any versions than that PR should be as well.
2. We could consider using the same default as MySQL: /tmp/mysql.sock. This would make it easier to connect with a standard MySQL client. However different distributions may override it (On Fedora it is in /var/lib/mysql/mysql.sock). Personally, I don't think we should do this.
3. This needs documentation updates:
   1. The default for the socket variable
   2. How to connect over a UNIX socket with mysql -S /tmp/tidb.sock (optional)
   3. How to connect over a UNIX socket with mysqlsh mysql://root@(/tmp/tidb.sock)/ (optional)

[morgo]

• I think this is fine since tidb using unix socket cannot restart if after SIGKILL #26058 is fixed. If this PR needs to be backported to any versions than that PR should be as well.

I added the label compatibility-breaker, because I have no intention to cherry pick.

We could consider using the same default as MySQL: /tmp/mysql.sock.

I actually deliberately avoided it, similar to how we don't use the MySQL Port. I'm worried some users will want to have both installed and get confused. If we ever aim for OS distros, they tend not to like this either.

This needs documentation updates:

Yes

[mjonss]

LGTM

[morgo]

/merge

[morgo]

/merge

[morgo]

/merge hold

[morgo]

/merge cancel

[morgo]

This looks to be blocked on an approving reviewer. Canceling merge so it doesn't block other PRs.

[bb7133]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: a7305c0

[dveeden]

The tidb-server --help output doesn't show the new default.

[dvaneeden@dve-carbon tidb]$ ./bin/tidb-server -V
Release Version: v5.3.0-alpha-1168-geca2dbb68
Edition: Community
Git Commit Hash: eca2dbb681cc89729fc849c0b6fc5ed246d6c8d2
Git Branch: master
UTC Build Time: 2021-10-21 07:26:53
GoVersion: go1.16.8
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false
[dvaneeden@dve-carbon tidb]$ ./bin/tidb-server --help 2>&1 | egrep -A1 '\-(socket|store) '
  -socket string
    	The socket file to use for connection.
--
  -store string
    	registered store name, [tikv, mocktikv, unistore] (default "unistore")

Looks like this is easy to fix:

[dvaneeden@dve-carbon tidb]$ git diff -U0
diff --git a/tidb-server/main.go b/tidb-server/main.go
index ae89bed91..37cf4d2db 100644
--- a/tidb-server/main.go
+++ b/tidb-server/main.go
@@ -128 +128 @@ var (
-       socket           = flag.String(nmSocket, "", "The socket file to use for connection.")
+       socket           = flag.String(nmSocket, "/tmp/tidb.sock", "The socket file to use for connection.")
[dvaneeden@dve-carbon tidb]$ ./bin/tidb-server --help 2>&1 | egrep -A1 '\-(socket|store) '
  -socket string
    	The socket file to use for connection. (default "/tmp/tidb.sock")
--
  -store string
    	registered store name, [tikv, mocktikv, unistore] (default "unistore")

[morgo]

Thanks! I'll fix it.