bad connection

[LeeDF]

Issue description

bad connection
$ wrk -c300 -d10m -t8 url
SetMaxOpenConns(100)
When wrk just started, Occasional bad connection error, And the number of mysql PROCESSLIST is less than 100, around 70
I modified the file

database/sql/sql.go 

func OpenDB(c driver.Connector) *DB {
	ctx, cancel := context.WithCancel(context.Background())
	db := &DB{
		connector:    c,
		openerCh:     make(chan struct{}, connectionRequestQueueSize),
		resetterCh:   make(chan *driverConn, 50),
		lastPut:      make(map[*driverConn]string),
		connRequests: make(map[uint64]chan connRequest),
		stop:         cancel,
	}

	go db.connectionOpener(ctx)
	go db.connectionResetter(ctx)

	return db
}

Changed the buffer length of resetterCh

resetterCh:   make(chan *driverConn, 100),

Solved the bad connection problem, and the number of mysql PROCESSLIST instantly reached 100

Example code

If possible, please enter some example code here to reproduce the issue.

Error log

bad connection

Configuration

Driver version (or git SHA):

Go version: run go version in your console
1.14
Server version: E.g. MySQL 5.6, MariaDB 10.0.20

Server OS: E.g. Debian 8.1 (Jessie), Windows 10

[methane]

Duplicate of golang/go#31480
Use Go 1.15.

[herry-go]

When the server resource consumption is small, a small number of errors are reported during the pressure test: the error rate is lower than 0.01%, but this error will occur every time;

qps：5000/s

I found that when I get a connection from the connection pool, I must judge whether the connection is expired, resulting in bad connection

in func (db *DB) conn() {
conn.inUse = true
if conn.expired(lifetime) {
db.maxLifetimeClosed++
db.mu.Unlock()
conn.Close()
return nil, driver.ErrBadConn
}
}

[fauzan05]

You must close your connection after you used. use Close() method to close your connection after you used.