use last second copy rate to project ETA (#1231)

* use current copy rate to project ETA

* make linter happy

* Replace `tests.ExpectEquals` with `require.Equal` in tests

---------

Co-authored-by: meiji163 <[email protected]>

Author: morgo

go/base/context.go

@@ -194,6 +194,7 @@ type MigrationContext struct {
 	CurrentLag                             int64
 	currentProgress                        uint64
 	etaNanoseonds                          int64
+	EtaRowsPerSecond                       int64
 	ThrottleHTTPIntervalMillis             int64
 	ThrottleHTTPStatusCode                 int64
 	ThrottleHTTPTimeoutMillis              int64

go/logic/migrator.go

@@ -819,11 +819,18 @@ func (this *Migrator) initiateStatus() {
 	this.printStatus(ForcePrintStatusAndHintRule)
 	ticker := time.NewTicker(time.Second)
 	defer ticker.Stop()
+	var previousCount int64
 	for range ticker.C {
 		if atomic.LoadInt64(&this.finishedMigrating) > 0 {
 			return
 		}
 		go this.printStatus(HeuristicPrintStatusRule)
+		totalCopied := atomic.LoadInt64(&this.migrationContext.TotalRowsCopied)
+		if previousCount > 0 {
+			copiedThisLoop := totalCopied - previousCount
+			atomic.StoreInt64(&this.migrationContext.EtaRowsPerSecond, copiedThisLoop)
+		}
+		previousCount = totalCopied
 	}
 }
 
@@ -925,9 +932,20 @@ func (this *Migrator) getMigrationETA(rowsEstimate int64) (eta string, duration
 		duration = 0
 	} else if progressPct >= 0.1 {
 		totalRowsCopied := this.migrationContext.GetTotalRowsCopied()
-		elapsedRowCopySeconds := this.migrationContext.ElapsedRowCopyTime().Seconds()
-		totalExpectedSeconds := elapsedRowCopySeconds * float64(rowsEstimate) / float64(totalRowsCopied)
-		etaSeconds := totalExpectedSeconds - elapsedRowCopySeconds
+		etaRowsPerSecond := atomic.LoadInt64(&this.migrationContext.EtaRowsPerSecond)
+		var etaSeconds float64
+		// If there is data available on our current row-copies-per-second rate, use it.
+		// Otherwise we can fallback to the total elapsed time and extrapolate.
+		// This is going to be less accurate on a longer copy as the insert rate
+		// will tend to slow down.
+		if etaRowsPerSecond > 0 {
+			remainingRows := float64(rowsEstimate) - float64(totalRowsCopied)
+			etaSeconds = remainingRows / float64(etaRowsPerSecond)
+		} else {
+			elapsedRowCopySeconds := this.migrationContext.ElapsedRowCopyTime().Seconds()
+			totalExpectedSeconds := elapsedRowCopySeconds * float64(rowsEstimate) / float64(totalRowsCopied)
+			etaSeconds = totalExpectedSeconds - elapsedRowCopySeconds
+		}
 		if etaSeconds >= 0 {
 			duration = time.Duration(etaSeconds) * time.Second
 		} else {

go/logic/migrator_test.go

@@ -215,6 +215,15 @@ func TestMigratorGetMigrationStateAndETA(t *testing.T) {
 		require.Equal(t, "4h29m44s", eta)
 		require.Equal(t, "4h29m44s", etaDuration.String())
 	}
+	{
+		// Test using rows-per-second added data.
+		migrationContext.TotalRowsCopied = 456
+		migrationContext.EtaRowsPerSecond = 100
+		state, eta, etaDuration := migrator.getMigrationStateAndETA(123456)
+		require.Equal(t, "migrating", state)
+		require.Equal(t, "20m30s", eta)
+		require.Equal(t, "20m30s", etaDuration.String())
+	}
 	{
 		migrationContext.TotalRowsCopied = 456
 		state, eta, etaDuration := migrator.getMigrationStateAndETA(456)