Sketch parallelization (not tested).

txcache/selectionUsingMerges.go

@@ -1,7 +1,16 @@
 package txcache
 
+import "sync"
+
 type BunchOfTransactions []*WrappedTransaction
 
+const numJobsForMerging = 4
+
+type mergingJob struct {
+	input  []BunchOfTransactions
+	output BunchOfTransactions
+}
+
 func (cache *TxCache) selectTransactionsUsingMerges(gasRequested uint64) BunchOfTransactions {
 	senders := cache.getSenders()
 	bunches := make([]BunchOfTransactions, 0, len(senders))
@@ -10,12 +19,7 @@ func (cache *TxCache) selectTransactionsUsingMerges(gasRequested uint64) BunchOf
 		bunches = append(bunches, sender.getTxsWithoutGaps())
 	}
 
-	// If number of bunches is odd, add a phony bunch (to ease pairing logic).
-	if len(bunches)%2 == 1 {
-		bunches = append(bunches, make(BunchOfTransactions, 0))
-	}
-
-	mergedBunch := mergeBunchesOfTransactions(bunches)[0]
+	mergedBunch := mergeBunchesOfTransactionsInParallel(bunches)
 	selection := selectUntilReachedGasRequested(mergedBunch, gasRequested)
 	return selection
 }
@@ -34,6 +38,48 @@ func selectUntilReachedGasRequested(bunch BunchOfTransactions, gasRequested uint
 	return bunch
 }
 
+func mergeBunchesOfTransactionsInParallel(bunches []BunchOfTransactions) BunchOfTransactions {
+	// If number of bunches is odd, add a phony bunch (to ease pairing logic).
+	if len(bunches)%2 == 1 {
+		bunches = append(bunches, make(BunchOfTransactions, 0))
+	}
+
+	jobs := make([]*mergingJob, numJobsForMerging)
+
+	for i := 0; i < numJobsForMerging; i++ {
+		jobs[i] = &mergingJob{
+			input: make([]BunchOfTransactions, 0, len(bunches)/numJobsForMerging),
+		}
+	}
+
+	for i, bunch := range bunches {
+		jobs[i%numJobsForMerging].input = append(jobs[i%numJobsForMerging].input, bunch)
+	}
+
+	// Run jobs in parallel
+	wg := sync.WaitGroup{}
+
+	for _, job := range jobs {
+		wg.Add(1)
+
+		go func(job *mergingJob) {
+			job.output = mergeBunchesOfTransactions(job.input)[0]
+			defer wg.Done()
+		}(job)
+	}
+
+	wg.Wait()
+
+	// Merge the results of the jobs
+	outputBunchesOfJobs := make([]BunchOfTransactions, 0, numJobsForMerging)
+
+	for _, job := range jobs {
+		outputBunchesOfJobs = append(outputBunchesOfJobs, job.output)
+	}
+
+	return mergeBunchesOfTransactions(outputBunchesOfJobs)[0]
+}
+
 func mergeBunchesOfTransactions(bunches []BunchOfTransactions) []BunchOfTransactions {
 	if len(bunches) == 1 {
 		return bunches