From 0e3efb6ea8b96f0adee424391fd1c416d5ec35dd Mon Sep 17 00:00:00 2001
From: Leon Yang <yangxin@pingcap.com>
Date: Tue, 19 Nov 2024 16:15:20 +0800
Subject: [PATCH] Lightning: Skip apply ioworkers when seek(0, io.SeekCurrent)
 (#57454)

close pingcap/tidb#57413
---
 pkg/lightning/mydump/reader.go | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/pkg/lightning/mydump/reader.go b/pkg/lightning/mydump/reader.go
index b5e21583105e3..c70328c6d8d9f 100644
--- a/pkg/lightning/mydump/reader.go
+++ b/pkg/lightning/mydump/reader.go
@@ -189,7 +189,8 @@ func (pr PooledReader) Read(p []byte) (n int, err error) {
 
 // Seek implements io.Seeker
 func (pr PooledReader) Seek(offset int64, whence int) (int64, error) {
-	if pr.ioWorkers != nil {
+	// Seek(0, io.SeekCurrent) is used to get the current offset, which will not cause any Disk I/O.
+	if pr.ioWorkers != nil && !(offset == 0 && whence == io.SeekCurrent) {
 		w := pr.ioWorkers.Apply()
 		defer pr.ioWorkers.Recycle(w)
 	}