From e88707c6fd55c567b9b272f9e7547a751e6c0004 Mon Sep 17 00:00:00 2001
From: Jussi Saurio <jussi.saurio@gmail.com>
Date: Thu, 31 Jul 2025 13:51:39 +0300
Subject: [PATCH] fix/wal: only rollback WAL if txn was write

---
 core/lib.rs           |  2 +-
 core/storage/pager.rs | 21 ++++++++++++++++-----
 core/storage/wal.rs   |  3 ++-
 3 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/core/lib.rs b/core/lib.rs
index 6f26ea0d0..318ca4f78 100644
--- a/core/lib.rs
+++ b/core/lib.rs
@@ -1190,7 +1190,7 @@ impl Connection {
                 wal.end_read_tx();
             }
             // remove all non-commited changes in case if WAL session left some suffix without commit frame
-            pager.rollback(false, self)?;
+            pager.rollback(false, self, true)?;
         }
 
         // let's re-parse schema from scratch if schema cookie changed compared to the our in-memory view of schema
diff --git a/core/storage/pager.rs b/core/storage/pager.rs
index 97979b43e..f3b6be3d0 100644
--- a/core/storage/pager.rs
+++ b/core/storage/pager.rs
@@ -815,14 +815,15 @@ impl Pager {
     ) -> Result<IOResult<PagerCommitResult>> {
         tracing::trace!("end_tx(rollback={})", rollback);
         if rollback {
-            if matches!(
+            let is_write = matches!(
                 connection.transaction_state.get(),
                 TransactionState::Write { .. }
-            ) {
+            );
+            if is_write {
                 self.wal.borrow().end_write_tx();
             }
             self.wal.borrow().end_read_tx();
-            self.rollback(schema_did_change, connection)?;
+            self.rollback(schema_did_change, connection, is_write)?;
             return Ok(IOResult::Done(PagerCommitResult::Rollback));
         }
         let commit_status = self.commit_dirty_pages(wal_checkpoint_disabled)?;
@@ -1799,9 +1800,17 @@ impl Pager {
         &self,
         schema_did_change: bool,
         connection: &Connection,
+        is_write: bool,
     ) -> Result<(), LimboError> {
         tracing::debug!(schema_did_change);
-        self.dirty_pages.borrow_mut().clear();
+        if is_write {
+            self.dirty_pages.borrow_mut().clear();
+        } else {
+            turso_assert!(
+                self.dirty_pages.borrow().is_empty(),
+                "dirty pages should be empty for read txn"
+            );
+        }
         let mut cache = self.page_cache.write();
 
         self.reset_internal_states();
@@ -1811,7 +1820,9 @@ impl Pager {
         if schema_did_change {
             connection.schema.replace(connection._db.clone_schema()?);
         }
-        self.wal.borrow_mut().rollback()?;
+        if is_write {
+            self.wal.borrow_mut().rollback()?;
+        }
 
         Ok(())
     }
diff --git a/core/storage/wal.rs b/core/storage/wal.rs
index f3b67f08b..3ef4df3b8 100644
--- a/core/storage/wal.rs
+++ b/core/storage/wal.rs
@@ -1292,6 +1292,7 @@ impl WalFile {
 
         let header = unsafe { shared.get().as_mut().unwrap().wal_header.lock() };
         let last_checksum = unsafe { (*shared.get()).last_checksum };
+        let start_pages_in_frames = unsafe { (*shared.get()).pages_in_frames.lock().len() };
         Self {
             io,
             // default to max frame in WAL, so that when we read schema we can read from WAL too if it's there.
@@ -1315,7 +1316,7 @@ impl WalFile {
             last_checksum,
             prev_checkpoint: CheckpointResult::default(),
             checkpoint_guard: None,
-            start_pages_in_frames: 0,
+            start_pages_in_frames,
             header: *header,
         }
     }