client: Add support for Session Tracking

[dveeden]

This work was triggered by this: #1067 (comment)

Tested with:

mysql-8.4.7 [(none)]> SHOW GLOBAL VARIABLES LIKE 'session\_track\_%';
+--------------------------------+------------------------------------------------------------------------------------------+
| Variable_name                  | Value                                                                                    |
+--------------------------------+------------------------------------------------------------------------------------------+
| session_track_gtids            | ALL_GTIDS                                                                                |
| session_track_schema           | ON                                                                                       |
| session_track_state_change     | ON                                                                                       |
| session_track_system_variables | time_zone,autocommit,character_set_client,character_set_results,character_set_connection |
| session_track_transaction_info | CHARACTERISTICS                                                                          |
+--------------------------------+------------------------------------------------------------------------------------------+
5 rows in set (0.002 sec)

package main

import (
	"fmt"

	"github.com/go-mysql-org/go-mysql/client"
	"github.com/go-mysql-org/go-mysql/mysql"
)

func main() {
	conn, err := client.Connect("127.0.0.1:3306", "root", "", "", func(conn *client.Conn) error {
		conn.SetCapability(mysql.CLIENT_SESSION_TRACK)
		return nil
	})
	if err != nil {
		panic(err)
	}
	defer conn.Quit()

	res, _ := conn.Execute("SELECT VERSION() AS ver")
	version, _ := res.GetStringByName(0, "ver")
	res.Close()
	fmt.Println(version)

	res, err = conn.UseDBWithResult("mysql")
	fmt.Printf("session tracking: %#v\n", res.SessionTracking)
	res.Close()

	res, _ = conn.Execute("SET SESSION autocommit=0")
	fmt.Printf("session tracking: %#v\n", res.SessionTracking)
	res.Close()

	res, _ = conn.Execute("SET SESSION autocommit=1")
	fmt.Printf("session tracking: %#v\n", res.SessionTracking)
	res.Close()

	res, _ = conn.Execute("START TRANSACTION READ ONLY")
	fmt.Printf("session tracking: %#v\n", res.SessionTracking)
	res.Close()

	res, _ = conn.Execute("START TRANSACTION READ WRITE")
	fmt.Printf("session tracking: %#v\n", res.SessionTracking)
	res.Close()

	res, _ = conn.Execute("ROLLBACK")
	fmt.Printf("session tracking: %#v\n", res.SessionTracking)
	res.Close()

	res, err = conn.Execute("CREATE SCHEMA test")
	if err == nil {
		fmt.Printf("session tracking: %#v\n", res.SessionTracking)
		res.Close()
	}

	res, _ = conn.UseDBWithResult("test")
	fmt.Printf("session tracking: %#v\n", res.SessionTracking)

	res, _ = conn.Execute("CREATE TABLE IF NOT EXISTS t(id int primary key)")
	fmt.Printf("session tracking: %#v\n", res.SessionTracking)
	res.Close()

	res, _ = conn.Execute("DELETE FROM t")
	fmt.Printf("session tracking: %#v\n", res.SessionTracking)
	res.Close()

	res, _ = conn.Execute("INSERT INTO t VALUES (1),(2),(3)")
	fmt.Printf("StatusMessage: %s\n", res.StatusMessage)
	fmt.Printf("session tracking: %#v\n", res.SessionTracking)
	res.Close()

	res, _ = conn.Execute("SET GTID_NEXT='AUTOMATIC:xmas'")
	fmt.Printf("session tracking: %#v\n", res.SessionTracking)
	res.Close()

	res, _ = conn.Execute("INSERT INTO t VALUES (4),(5),(6)")
	fmt.Printf("session tracking: %#v\n", res.SessionTracking)
	res.Close()

	res, _ = conn.Execute("SET @a := 12345")
	fmt.Printf("session tracking: %#v\n", res.SessionTracking)
	res.Close()
}

Output:

8.4.7
session tracking: &mysql.SessionTrackingInfo{GTID:"", TransactionState:"", Variables:map[string]string(nil), Schema:"mysql", State:"1", Characteristics:""}
session tracking: &mysql.SessionTrackingInfo{GTID:"f4993c5e-d353-11f0-9b5f-eede6d5626c8:1-279:xmas:1-30", TransactionState:"", Variables:map[string]string{"autocommit":"OFF"}, Schema:"", State:"1", Characteristics:""}
session tracking: &mysql.SessionTrackingInfo{GTID:"f4993c5e-d353-11f0-9b5f-eede6d5626c8:1-279:xmas:1-30", TransactionState:"", Variables:map[string]string{"autocommit":"ON"}, Schema:"", State:"1", Characteristics:""}
session tracking: &mysql.SessionTrackingInfo{GTID:"", TransactionState:"T_______", Variables:map[string]string(nil), Schema:"", State:"", Characteristics:"START TRANSACTION READ ONLY;"}
session tracking: &mysql.SessionTrackingInfo{GTID:"", TransactionState:"", Variables:map[string]string(nil), Schema:"", State:"", Characteristics:"START TRANSACTION READ WRITE;"}
session tracking: &mysql.SessionTrackingInfo{GTID:"", TransactionState:"________", Variables:map[string]string(nil), Schema:"", State:"", Characteristics:""}
session tracking: &mysql.SessionTrackingInfo{GTID:"", TransactionState:"", Variables:map[string]string(nil), Schema:"test", State:"1", Characteristics:""}
session tracking: &mysql.SessionTrackingInfo{GTID:"f4993c5e-d353-11f0-9b5f-eede6d5626c8:1-280:xmas:1-30", TransactionState:"", Variables:map[string]string(nil), Schema:"", State:"", Characteristics:""}
session tracking: &mysql.SessionTrackingInfo{GTID:"f4993c5e-d353-11f0-9b5f-eede6d5626c8:1-281:xmas:1-30", TransactionState:"", Variables:map[string]string(nil), Schema:"", State:"", Characteristics:""}
StatusMessage: Records: 3  Duplicates: 0  Warnings: 0
session tracking: &mysql.SessionTrackingInfo{GTID:"f4993c5e-d353-11f0-9b5f-eede6d5626c8:1-282:xmas:1-30", TransactionState:"", Variables:map[string]string(nil), Schema:"", State:"", Characteristics:""}
session tracking: &mysql.SessionTrackingInfo{GTID:"f4993c5e-d353-11f0-9b5f-eede6d5626c8:1-282:xmas:1-30", TransactionState:"", Variables:map[string]string(nil), Schema:"", State:"1", Characteristics:""}
session tracking: &mysql.SessionTrackingInfo{GTID:"f4993c5e-d353-11f0-9b5f-eede6d5626c8:1-282:xmas:1-31", TransactionState:"", Variables:map[string]string(nil), Schema:"", State:"", Characteristics:""}
session tracking: &mysql.SessionTrackingInfo{GTID:"f4993c5e-d353-11f0-9b5f-eede6d5626c8:1-282:xmas:1-31", TransactionState:"", Variables:map[string]string(nil), Schema:"", State:"1", Characteristics:""}

[dveeden]

We could automatically change c.db when there is a SESSION_TRACK_SCHEMA, but I don't think we should.

One of the possible usecases is this:

1. Write to a primary, Use session tracking to get the OWN_GTID.
2. Read from a replica with WAIT_FOR_EXECUTED_GTID_SET().

This gives a way to improve the read-after-write experience without having to always read from the primary.

[lance6716]

I need some time to learn https://dev.mysql.com/doc/refman/8.4/en/session-state-tracking.html

[dveeden]

Another implementation method could be a per connection channel with the session tracking info