read-write distinction in the tx API

cozo-core/src/runtime/db.rs

@@ -122,7 +122,7 @@ where
     }
     fn transact(&self) -> Result<SessionTx> {
         let ret = SessionTx {
-            tx: Box::new(self.db.transact()?),
+            tx: Box::new(self.db.transact(false)?),
             mem_store_id: Default::default(),
             relation_store_id: self.relation_store_id.clone(),
         };
@@ -130,7 +130,7 @@ where
     }
     fn transact_write(&self) -> Result<SessionTx> {
         let ret = SessionTx {
-            tx: Box::new(self.db.transact()?),
+            tx: Box::new(self.db.transact(true)?),
             mem_store_id: Default::default(),
             relation_store_id: self.relation_store_id.clone(),
         };
@@ -716,7 +716,7 @@ where
             LARGEST_UTF_CHAR,
         )))])
         .encode_as_key(RelationId::SYSTEM);
-        let tx = self.db.transact()?;
+        let tx = self.db.transact(false)?;
         let mut collected = vec![];
         for kv_res in tx.range_scan_raw(&lower, &upper) {
             let (k_slice, v_slice) = kv_res?;

cozo-core/src/storage/mod.rs

@@ -13,7 +13,7 @@ pub(crate) mod tikv;
 pub trait Storage {
     type Tx: StoreTx;
 
-    fn transact(&self) -> Result<Self::Tx>;
+    fn transact(&self, write: bool) -> Result<Self::Tx>;
     fn del_range(&self, lower: &[u8], upper: &[u8]) -> Result<()>;
     fn range_compact(&self, lower: &[u8], upper: &[u8]) -> Result<()>;
 }

cozo-core/src/storage/rocks.rs

@@ -90,7 +90,7 @@ impl RocksDbStorage {
 impl Storage for RocksDbStorage {
     type Tx = RocksDbTx;
 
-    fn transact(&self) -> Result<Self::Tx> {
+    fn transact(&self, _write: bool) -> Result<Self::Tx> {
         let db_tx = self.db.transact().set_snapshot(true).start();
         Ok(RocksDbTx { db_tx })
     }

cozo-core/src/storage/sled.rs

@@ -34,7 +34,7 @@ const DEL_MARKER: u8 = 0;
 impl Storage for SledStorage {
     type Tx = SledTx;
 
-    fn transact(&self) -> Result<Self::Tx> {
+    fn transact(&self, _write: bool) -> Result<Self::Tx> {
         Ok(SledTx {
             db: self.db.clone(),
             changes: Default::default(),