Move wait_for_previous_l1_batch_hash() invocation

core/lib/zksync_core/src/state_keeper/io/mempool.rs

@@ -161,8 +161,6 @@ impl StateKeeperIO for MempoolIO {
         max_wait: Duration,
     ) -> Option<(SystemEnv, L1BatchEnv)> {
         let deadline = Instant::now() + max_wait;
-        // FIXME: why do we wait for hash immediately and not below? (changed in #809)
-        let prev_l1_batch_hash = self.wait_for_previous_l1_batch_hash().await;
 
         // Block until at least one transaction in the mempool can match the filter (or timeout happens).
         // This is needed to ensure that block timestamp is not too old.
@@ -194,12 +192,13 @@ impl StateKeeperIO for MempoolIO {
                 protocol_version.into(),
             )
             .await;
-            // We only need to get the root hash when we're certain that we have a new transaction.
             if !self.mempool.has_next(&self.filter) {
                 tokio::time::sleep(self.delay_interval).await;
                 continue;
             }
 
+            // We only need to get the root hash when we're certain that we have a new transaction.
+            let prev_l1_batch_hash = self.wait_for_previous_l1_batch_hash().await;
             return Some(l1_batch_params(
                 self.current_l1_batch_number,
                 self.fee_account,