Dont allocate fresh page1 if it's in the WAL

core/lib.rs

@@ -202,12 +202,14 @@ impl Database {
                 shared_wal,
                 buffer_pool.clone(),
             )));
+            let is_empty = false;
             let pager = Rc::new(Pager::new(
                 self.db_file.clone(),
                 wal,
                 self.io.clone(),
                 Arc::new(RwLock::new(DumbLruPageCache::default())),
                 buffer_pool,
+                is_empty,
             )?);
 
             let header = pager.db_header()?;
@@ -230,12 +232,14 @@ impl Database {
             })
         } else {
             let dummy_wal = Rc::new(RefCell::new(DummyWAL {}));
+            let is_empty = true;
             let mut pager = Pager::new(
                 self.db_file.clone(),
                 dummy_wal,
                 self.io.clone(),
                 Arc::new(RwLock::new(DumbLruPageCache::default())),
                 buffer_pool.clone(),
+                is_empty,
             )?;
             let header = pager.db_header()?;
             let wal_path = format!("{}-wal", self.path);

core/storage/btree.rs

@@ -6868,7 +6868,7 @@ mod tests {
         let wal = Rc::new(RefCell::new(wal_file));
 
         let page_cache = Arc::new(parking_lot::RwLock::new(DumbLruPageCache::new(2000)));
-        let pager = { Pager::new(db_file, wal, io, page_cache, buffer_pool).unwrap() };
+        let pager = { Pager::new(db_file, wal, io, page_cache, buffer_pool, true).unwrap() };
         let pager = Rc::new(pager);
         // FIXME: handle page cache is full
         pager.allocate_page1().unwrap();
@@ -7390,6 +7390,7 @@ mod tests {
                 io,
                 Arc::new(parking_lot::RwLock::new(DumbLruPageCache::new(10))),
                 buffer_pool,
+                true,
             )
             .unwrap(),
         );

core/storage/pager.rs

@@ -14,7 +14,7 @@ use parking_lot::RwLock;
 use std::cell::{RefCell, UnsafeCell};
 use std::collections::HashSet;
 use std::rc::Rc;
-use std::sync::atomic::{AtomicUsize, Ordering};
+use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
 use std::sync::Arc;
 use tracing::{trace, Level};
 
@@ -214,8 +214,8 @@ pub struct Pager {
     checkpoint_inflight: Rc<RefCell<usize>>,
     syncing: Rc<RefCell<bool>>,
     auto_vacuum_mode: RefCell<AutoVacuumMode>,
-    /// Number of pages in the database file.
-    pub npages: AtomicUsize,
+    /// Is the db empty? This is signified by 0-sized database and nonexistent WAL.
+    pub is_empty: AtomicBool,
 }
 
 #[derive(Debug, Copy, Clone)]
@@ -249,17 +249,8 @@ impl Pager {
         io: Arc<dyn crate::io::IO>,
         page_cache: Arc<RwLock<DumbLruPageCache>>,
         buffer_pool: Rc<BufferPool>,
+        is_empty: bool,
     ) -> Result<Self> {
-        let npages = if db_file.size().unwrap() > 0 {
-            let db_header = Pager::begin_open(db_file.clone()).unwrap();
-            // ensure db header is there
-            io.run_once().unwrap();
-            let size = db_header.lock().database_size;
-            size as usize
-        } else {
-            0
-        };
-
         Ok(Self {
             db_file,
             wal,
@@ -275,7 +266,7 @@ impl Pager {
             checkpoint_inflight: Rc::new(RefCell::new(0)),
             buffer_pool,
             auto_vacuum_mode: RefCell::new(AutoVacuumMode::None),
-            npages: AtomicUsize::new(npages),
+            is_empty: AtomicBool::new(is_empty),
         })
     }
 
@@ -284,7 +275,7 @@ impl Pager {
     }
 
     pub fn db_header(&self) -> Result<DatabaseHeader> {
-        if self.npages.load(Ordering::SeqCst) == 0 {
+        if self.is_empty.load(Ordering::SeqCst) {
             return Ok(DatabaseHeader::default());
         }
 
@@ -1007,7 +998,7 @@ impl Pager {
 
     pub fn allocate_page1(&self) -> Result<PageRef> {
         let default_header = DatabaseHeader::default();
-        self.npages.fetch_add(1, Ordering::SeqCst);
+        self.is_empty.store(false, Ordering::SeqCst);
         let page = allocate_page(1, &self.buffer_pool, 0);
 
         let page1 = Arc::new(BTreePageInner {
@@ -1046,7 +1037,7 @@ impl Pager {
     pub fn allocate_page(&self) -> Result<PageRef> {
         let mut header = self.db_header()?;
         header.database_size += 1;
-        self.npages.fetch_add(1, Ordering::SeqCst);
+        self.is_empty.store(false, Ordering::SeqCst);
 
         tracing::debug!("allocate_page(database_size={})", header.database_size);
 
@@ -1426,7 +1417,7 @@ mod ptrmap_tests {
             buffer_pool.clone(),
         )));
 
-        let pager = Pager::new(db_file, wal, io, page_cache, buffer_pool).unwrap();
+        let pager = Pager::new(db_file, wal, io, page_cache, buffer_pool, true).unwrap();
         pager.set_auto_vacuum_mode(AutoVacuumMode::Full);
 
         //  Allocate all the pages as btree root pages

core/vdbe/execute.rs

@@ -1685,7 +1685,7 @@ pub fn op_transaction(
         }
 
         // We allocate the first page lazily in the *first* write transaction
-        if conn.pager.npages.load(Ordering::SeqCst) == 0 {
+        if conn.pager.is_empty.load(Ordering::SeqCst) {
             conn.pager.allocate_page1()?;
         }
     }
@@ -5221,6 +5221,7 @@ pub fn op_open_ephemeral(
         io,
         page_cache,
         buffer_pool.clone(),
+        true,
     )?);
 
     let header = pager.db_header()?;