fix(api): Return on duplicate earlier (matter-labs#1059)

## What ❔

Return on tx duplicate earlier, putting less load on DB

## Why ❔

Put less load on DB

## Checklist

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- [ ] Tests for the changes have been added / updated.
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---------

Co-authored-by: Roman Brodetski <rb@matterlabs.dev>

core/lib/dal/src/tests/mod.rs

@@ -149,7 +149,7 @@ async fn workflow_with_submit_tx_equal_hashes() {
         .insert_transaction_l2(tx, mock_tx_execution_metrics())
         .await;
 
-    assert_eq!(result, L2TxSubmissionResult::Replaced);
+    assert_eq!(result, L2TxSubmissionResult::Duplicate);
 }
 
 #[tokio::test]

core/lib/dal/src/transactions_dal.rs

@@ -256,6 +256,27 @@ impl TransactionsDal<'_, '_> {
     ) -> L2TxSubmissionResult {
         {
             let tx_hash = tx.hash();
+            let is_duplicate = sqlx::query!(
+                r#"
+                SELECT
+                    TRUE
+                FROM
+                    transactions
+                WHERE
+                    hash = $1
+                "#,
+                tx_hash.as_bytes(),
+            )
+            .fetch_optional(self.storage.conn())
+            .await
+            .unwrap()
+            .is_some();
+
+            if is_duplicate {
+                tracing::debug!("Prevented inserting duplicate L2 transaction {tx_hash:?} to DB");
+                return L2TxSubmissionResult::Duplicate;
+            }
+
             let initiator_address = tx.initiator_account();
             let contract_address = tx.execute.contract_address.as_bytes();
             let json_data = serde_json::to_value(&tx.execute)
@@ -411,6 +432,7 @@ impl TransactionsDal<'_, '_> {
                     if let error::Error::Database(ref error) = err {
                         if let Some(constraint) = error.constraint() {
                             if constraint == "transactions_pkey" {
+                                tracing::debug!("Attempted to insert duplicate L2 transaction {tx_hash:?} to DB");
                                 return L2TxSubmissionResult::Duplicate;
                             }
                         }