fix(time): remove cached time optimization (#3611)

Author: ndyakov

internal/pool/conn.go

@@ -27,16 +27,17 @@ var (
 	errConnNotAvailableForWrite = errors.New("redis: connection not available for write operation")
 )
 
-// getCachedTimeNs returns the current time in nanoseconds from the global cache.
-// This is updated every 50ms by a background goroutine, avoiding expensive syscalls.
-// Max staleness: 50ms.
+// getCachedTimeNs returns the current time in nanoseconds.
+// This function previously used a global cache updated by a background goroutine,
+// but that caused unnecessary CPU usage when the client was idle (ticker waking up
+// the scheduler every 50ms). We now use time.Now() directly, which is fast enough
+// on modern systems (vDSO on Linux) and only adds ~1-2% overhead in extreme
+// high-concurrency benchmarks while eliminating idle CPU usage.
 func getCachedTimeNs() int64 {
-	return globalTimeCache.nowNs.Load()
+	return time.Now().UnixNano()
 }
 
-// GetCachedTimeNs returns the current time in nanoseconds from the global cache.
-// This is updated every 50ms by a background goroutine, avoiding expensive syscalls.
-// Max staleness: 50ms.
+// GetCachedTimeNs returns the current time in nanoseconds.
 // Exported for use by other packages that need fast time access.
 func GetCachedTimeNs() int64 {
 	return getCachedTimeNs()

internal/pool/global_time_cache.go

@@ -178,9 +178,6 @@ func NewConnPool(opt *Options) *ConnPool {
 		p.connsMu.Unlock()
 	}
 
-	startGlobalTimeCache()
-	subscribeToGlobalTimeCache()
-
 	return p
 }
 
@@ -981,9 +978,6 @@ func (p *ConnPool) Close() error {
 		return ErrClosed
 	}
 
-	unsubscribeFromGlobalTimeCache()
-	stopGlobalTimeCache()
-
 	var firstErr error
 	p.connsMu.Lock()
 	for _, cn := range p.conns {