From c633eb1fea919516211aeec8dc633e253cf17747 Mon Sep 17 00:00:00 2001
From: Toni Spets <toni.spets@beeper.com>
Date: Sat, 16 Dec 2023 12:01:33 +0200
Subject: [PATCH] Ignore WAL indices before snapshot that is being restored
 (#527)

---
 replica.go | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/replica.go b/replica.go
index b8b3a9e5..6872bca1 100644
--- a/replica.go
+++ b/replica.go
@@ -961,6 +961,7 @@ func (r *Replica) GenerationTimeBounds(ctx context.Context, generation string) (
 	}
 	defer sitr.Close()
 
+	minIndex, maxIndex := -1, -1
 	for sitr.Next() {
 		info := sitr.Snapshot()
 		if createdAt.IsZero() || info.CreatedAt.Before(createdAt) {
@@ -969,6 +970,12 @@ func (r *Replica) GenerationTimeBounds(ctx context.Context, generation string) (
 		if updatedAt.IsZero() || info.CreatedAt.After(updatedAt) {
 			updatedAt = info.CreatedAt
 		}
+		if minIndex == -1 || info.Index < minIndex {
+			minIndex = info.Index
+		}
+		if info.Index > maxIndex {
+			maxIndex = info.Index
+		}
 	}
 	if err := sitr.Close(); err != nil {
 		return createdAt, updatedAt, err
@@ -983,6 +990,9 @@ func (r *Replica) GenerationTimeBounds(ctx context.Context, generation string) (
 
 	for witr.Next() {
 		info := witr.WALSegment()
+		if info.Index < minIndex || info.Index > maxIndex {
+			continue
+		}
 		if createdAt.IsZero() || info.CreatedAt.Before(createdAt) {
 			createdAt = info.CreatedAt
 		}
@@ -1077,7 +1087,7 @@ func (r *Replica) Restore(ctx context.Context, opt RestoreOptions) (err error) {
 	}
 
 	// Compute list of offsets for each WAL index.
-	walSegmentMap, err := r.walSegmentMap(ctx, opt.Generation, opt.Index, opt.Timestamp)
+	walSegmentMap, err := r.walSegmentMap(ctx, opt.Generation, minWALIndex, opt.Index, opt.Timestamp)
 	if err != nil {
 		return fmt.Errorf("cannot find max wal index for restore: %w", err)
 	}
@@ -1285,7 +1295,7 @@ func (r *Replica) SnapshotIndexByIndex(ctx context.Context, generation string, i
 
 // walSegmentMap returns a map of WAL indices to their segments.
 // Filters by a max timestamp or a max index.
-func (r *Replica) walSegmentMap(ctx context.Context, generation string, maxIndex int, maxTimestamp time.Time) (map[int][]int64, error) {
+func (r *Replica) walSegmentMap(ctx context.Context, generation string, minIndex, maxIndex int, maxTimestamp time.Time) (map[int][]int64, error) {
 	itr, err := r.Client.WALSegments(ctx, generation)
 	if err != nil {
 		return nil, err
@@ -1301,6 +1311,8 @@ func (r *Replica) walSegmentMap(ctx context.Context, generation string, maxIndex
 			break // after max timestamp, skip
 		} else if info.Index > maxIndex {
 			break // after max index, skip
+		} else if info.Index < minIndex {
+			continue // before min index, continue
 		}
 
 		// Verify offsets are added in order.