fix: refactor InteractiveTransaction#depth to return Result<i32>

This change also removes an if statement that is redundant.

query-engine/core/src/interactive_transactions/manager.rs

@@ -114,12 +114,8 @@ impl ItxManager {
         if self.transactions.read().await.contains_key(&tx_id) {
             let transaction_entry = self.get_transaction(&tx_id, "begin").await?;
             let mut tx = transaction_entry.lock().await;
-            // If the transaction is already open, we need to create a savepoint.
-            if tx.depth() > 0 {
-                tx.create_savepoint().await?;
-            } else {
-                tx.begin().await?;
-            }
+            // The transaction is already open, so we need to create a savepoint.
+            tx.create_savepoint().await?;
         } else {
             // This task notifies the task spawned in `new()` method that the timeout for this
             // transaction has expired.
@@ -193,7 +189,7 @@ impl ItxManager {
     pub async fn commit_tx(&self, tx_id: &TxId) -> crate::Result<()> {
         let transaction_entry = self.get_transaction(tx_id, "commit").await?;
         let mut tx = transaction_entry.lock().await;
-        let depth = tx.depth();
+        let depth = tx.depth()?;
         if depth > 1 {
             tx.release_savepoint().await
         } else {
@@ -204,7 +200,7 @@ impl ItxManager {
     pub async fn rollback_tx(&self, tx_id: &TxId) -> crate::Result<()> {
         let transaction_entry = self.get_transaction(tx_id, "rollback").await?;
         let mut tx = transaction_entry.lock().await;
-        let depth = tx.depth();
+        let depth = tx.depth()?;
         if depth > 1 {
             tx.rollback_to_savepoint().await
         } else {

query-engine/core/src/interactive_transactions/transaction.rs

@@ -197,28 +197,9 @@ impl InteractiveTransaction {
         })
     }
 
-    pub fn depth(&mut self) -> i32 {
-        match self.state.as_open("depth") {
-            Ok(state) => state.depth(),
-            Err(_) => 0,
-        }
-    }
-
-    pub async fn begin(&mut self) -> crate::Result<()> {
-        tx_timeout!(self, "begin", async {
-            let name = self.name();
-            let conn = self.state.as_open("begin")?;
-            let span = info_span!("prisma:engine:itx_begin", user_facing = true);
-
-            if let Err(err) = conn.begin().instrument(span).await {
-                error!(?err, ?name, "transaction failed to begin");
-                let _ = self.rollback(false).await;
-                Err(err.into())
-            } else {
-                debug!(?name, "transaction started");
-                Ok(())
-            }
-        })
+    pub fn depth(&mut self) -> crate::Result<i32> {
+        let conn = self.state.as_open("depth")?;
+        Ok(conn.depth())
     }
 
     pub async fn commit(&mut self) -> crate::Result<()> {