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messager: avoid taking locks if there's no work to do #4745

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Merged
sougou merged 1 commit into from
Mar 31, 2019
Merged

messager: avoid taking locks if there's no work to do #4745

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10 changes: 10 additions & 0 deletions go/vt/vttablet/tabletserver/messager/engine.go
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Original file line number Diff line number Diff line change
Expand Up @@ -130,6 +130,11 @@ func (me *Engine) Subscribe(ctx context.Context, name string, send func(*sqltype
// LockDB obtains db locks for all messages that need to
// be updated and returns the counterpart unlock function.
func (me *Engine) LockDB(newMessages map[string][]*MessageRow, changedMessages map[string][]string) func() {
// Short-circuit to avoid taking any locks if there's nothing to do.
if len(newMessages) == 0 && len(changedMessages) == 0 {
return func() {}
}

// Build the set of affected messages tables.
combined := make(map[string]struct{})
for name := range newMessages {
Expand Down Expand Up @@ -174,6 +179,11 @@ func (me *Engine) LockDB(newMessages map[string][]*MessageRow, changedMessages m

// UpdateCaches updates the caches for the committed changes.
func (me *Engine) UpdateCaches(newMessages map[string][]*MessageRow, changedMessages map[string][]string) {
// Short-circuit to avoid taking any locks if there's nothing to do.
if len(newMessages) == 0 && len(changedMessages) == 0 {
return
}

me.mu.Lock()
defer me.mu.Unlock()
now := time.Now().UnixNano()
Expand Down