From 1e70e3404b9c475e58efbe0ee7906c873a571e1a Mon Sep 17 00:00:00 2001
From: Simone Gotti <simone.gotti@gmail.com>
Date: Tue, 5 Nov 2019 17:48:11 +0100
Subject: [PATCH] datamanager: skip already applied wals in writeDataSnapshot

As an optimization don't apply already applied wals.
---
 internal/datamanager/data.go | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/internal/datamanager/data.go b/internal/datamanager/data.go
index cdc5c8c..f6352c7 100644
--- a/internal/datamanager/data.go
+++ b/internal/datamanager/data.go
@@ -163,13 +163,28 @@ func (d *DataManager) writeDataSnapshot(ctx context.Context, wals []*WalData) er
 		Files:        make(map[string][]*DataStatusFile),
 	}
 
-	wi, err := d.walIndex(ctx, wals)
-	if err != nil {
+	curDataStatus, err := d.GetLastDataStatus()
+	if err != nil && !errors.Is(err, ErrNoDataStatus) {
 		return err
 	}
 
-	curDataStatus, err := d.GetLastDataStatus()
-	if err != nil && !errors.Is(err, ErrNoDataStatus) {
+	startWalIndex := 0
+	if curDataStatus != nil {
+		// skip wals already checkpointed in this data status
+		for i, wal := range wals {
+			if wal.WalSequence <= curDataStatus.WalSequence {
+				continue
+			}
+
+			startWalIndex = i
+			break
+		}
+	}
+
+	wals = wals[startWalIndex:]
+
+	wi, err := d.walIndex(ctx, wals)
+	if err != nil {
 		return err
 	}