From 0bd1b13b945524feabbf2b0f5d9a29e27f1c7cf8 Mon Sep 17 00:00:00 2001
From: Ben Johnson <benbjohnson@yahoo.com>
Date: Sun, 7 Mar 2021 07:48:43 -0700
Subject: [PATCH] Add wal validation debug information on error

This commit adds the WAL header and shadow path to "wal header mismatch"
errors to help debug issues. The mismatch seems to happen more often
than I would expect on restart. This error doesn't cause any corruption;
it simply causes a generation to restart which requires a snapshot.
---
 db.go | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/db.go b/db.go
index 73b9ea9..2b44bac 100644
--- a/db.go
+++ b/db.go
@@ -462,7 +462,7 @@ func (db *DB) init() (err error) {
 
 	// If we have an existing shadow WAL, ensure the headers match.
 	if err := db.verifyHeadersMatch(); err != nil {
-		log.Printf("%s: init: cannot determine last wal position, clearing generation (%s)", db.path, err)
+		log.Printf("%s: init: cannot determine last wal position, clearing generation; %s", db.path, err)
 		if err := os.Remove(db.GenerationNamePath()); err != nil && !os.IsNotExist(err) {
 			return fmt.Errorf("remove generation name: %w", err)
 		}
@@ -512,7 +512,7 @@ func (db *DB) verifyHeadersMatch() error {
 	}
 
 	if !bytes.Equal(hdr0, hdr1) {
-		return fmt.Errorf("wal header mismatch")
+		return fmt.Errorf("wal header mismatch %x <> %x on %s", hdr0, hdr1, shadowWALPath)
 	}
 	return nil
 }