Off topic question. But does anyone know how I can gain admin access on my
work computer?
On Thursday, June 29, 2017 at 12:01:16 AM UTC-7 Kai Zhang wrote:
> Go version 1.8.3
>
> In DB.QueryContext(), Go will close long live connection which exceeded
> the duration setted by DB.SetConnMaxLifetime(), the code is below
> database/sql/sql.go
> 895 func (db *DB) conn(ctx context.Context, strategy connReuseStrategy)
> (*driverConn, error) {
> 896 db.mu.Lock()
> 897 if db.closed {
> 898 db.mu.Unlock()
> 899 return nil, errDBClosed
> 900 }
> 901 // Check if the context is expired.
> 902 select {
> 903 default:
> 904 case <-ctx.Done():
> 905 db.mu.Unlock()
> 906 return nil, ctx.Err()
> 907 }
> 908 lifetime := db.maxLifetime
> 909
> 910 // Prefer a free connection, if possible.
> 911 numFree := len(db.freeConn)
> 912 if strategy == cachedOrNewConn && numFree > 0 {
> 913 conn := db.freeConn[0]
> 914 copy(db.freeConn, db.freeConn[1:])
> 915 db.freeConn = db.freeConn[:numFree-1]
> 916 conn.inUse = true
> 917 db.mu.Unlock()
> * 918 if conn.expired(lifetime) {*
> * 919 conn.Close()*
> 920 return nil, driver.ErrBadConn
> 921 }
>
>
> 922 return conn, nil
> 923 }
>
>
> The problem is if driver.Close() has some handshake to tear down the
> connection, this may introduce unexpected latency. But the driver.Conn
> interface not mention this.
> database/sql/driver/driver.go
> 143 type Conn interface {
> 144 // Prepare returns a prepared statement, bound to this connection.
> 145 Prepare(query string) (Stmt, error)
> 146
> 147 // Close invalidates and potentially stops any current
> 148 // prepared statements and transactions, marking this
> 149 // connection as no longer in use.
> 150 //
> 151 // Because the sql package maintains a free pool of
> 152 // connections and only calls Close when there's a surplus of
> 153 // idle connections, it shouldn't be necessary for drivers to
> 154 // do their own connection caching.
>
>
> 155 Close() error
> 156
> 157 // Begin starts and returns a new transaction.
> 158 //
> 159 // Deprecated: Drivers should implement ConnBeginTx instead (or
> additionally).
> 160 Begin() (Tx, error)
> 161 }
>
> There is already a goroutine to clean the connections, why still need a
> synchronous check?
> database/sql/sql.go
> 750 func (db *DB) connectionCleaner(d time.Duration) {
>
>
> 751 const minInterval = time.Second
> 752
> 753 if d < minInterval {
> 754 d = minInterval
> 755 }
> 756 t := time.NewTimer(d)
> 757
> 758 for {
> 759 select {
> 760 case <-t.C:
> 761 case <-db.cleanerCh: // maxLifetime was changed or db was
> closed.
> 762 }
> 763
> 764 db.mu.Lock()
> 765 d = db.maxLifetime
> 766 if db.closed || db.numOpen == 0 || d <= 0 {
> 767 db.cleanerCh = nil
> 768 db.mu.Unlock()
> 769 return
> 770 }
> 771
> 772 expiredSince := nowFunc().Add(-d)
> 773 var closing []*driverConn
> 774 for i := 0; i < len(db.freeConn); i++ {
> 775 c := db.freeConn[i]
> 776 if c.createdAt.Before(expiredSince) {
> 777 closing = append(closing, c)
> 778 last := len(db.freeConn) - 1
> 779 db.freeConn[i] = db.freeConn[last]
> 780 db.freeConn[last] = nil
> 781 db.freeConn = db.freeConn[:last]
> 782 i--
> 783 }
> 784 }
>
>
>
> Is this by design or need to be fixed?
>
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