Maintain original queue capacity for unprocessed packet buffer (#28661)

core/src/unprocessed_transaction_storage.rs

@@ -426,13 +426,15 @@ impl ThreadLocalUnprocessedPackets {
         let mut total_filter_packets_us: u64 = 0;
         let mut dropped_tx_before_forwarding_count: usize = 0;
 
-        let mut original_priority_queue = self.swap_priority_queue();
+        let mut original_priority_queue = self.take_priority_queue();
+        let original_capacity = original_priority_queue.capacity();
+        let mut new_priority_queue = MinMaxHeap::with_capacity(original_capacity);
 
         // indicates if `forward_buffer` still accept more packets, see details at
         // `ForwardPacketBatchesByAccounts.rs`.
         let mut accepting_packets = true;
         // batch iterate through self.unprocessed_packet_batches in desc priority order
-        let retained_priority_queue: MinMaxHeap<Arc<ImmutableDeserializedPacket>> =
+        new_priority_queue.extend(
             original_priority_queue
                 .drain_desc()
                 .chunks(batch_size)
@@ -522,11 +524,12 @@ impl ThreadLocalUnprocessedPackets {
                         );
                         packets_to_process
                     }
-                })
-                .collect();
+                }),
+        );
 
         // replace packet priority queue
-        self.unprocessed_packet_batches.packet_priority_queue = retained_priority_queue;
+        self.unprocessed_packet_batches.packet_priority_queue = new_priority_queue;
+        self.verify_priority_queue(original_capacity);
 
         inc_new_counter_info!(
             "banking_stage-dropped_tx_before_forwarding",
@@ -543,14 +546,30 @@ impl ThreadLocalUnprocessedPackets {
     }
 
     /// Take self.unprocessed_packet_batches's priority_queue out, leave empty MinMaxHeap in its place.
-    fn swap_priority_queue(&mut self) -> MinMaxHeap<Arc<ImmutableDeserializedPacket>> {
-        let capacity = self.unprocessed_packet_batches.capacity();
+    fn take_priority_queue(&mut self) -> MinMaxHeap<Arc<ImmutableDeserializedPacket>> {
         std::mem::replace(
             &mut self.unprocessed_packet_batches.packet_priority_queue,
-            MinMaxHeap::with_capacity(capacity),
+            MinMaxHeap::new(), // <-- no need to reserve capacity as we will replace this
         )
     }
 
+    /// Verify that the priority queue and map are consistent and that original capacity is maintained.
+    fn verify_priority_queue(&self, original_capacity: usize) {
+        // Assert unprocessed queue is still consistent and maintains original capacity
+        assert_eq!(
+            self.unprocessed_packet_batches
+                .packet_priority_queue
+                .capacity(),
+            original_capacity
+        );
+        assert_eq!(
+            self.unprocessed_packet_batches.packet_priority_queue.len(),
+            self.unprocessed_packet_batches
+                .message_hash_to_transaction
+                .len()
+        );
+    }
+
     /// sanitize un-forwarded packet into SanitizedTransaction for validation and forwarding.
     fn sanitize_unforwarded_packets(
         &mut self,
@@ -701,35 +720,31 @@ impl ThreadLocalUnprocessedPackets {
     where
         F: FnMut(&Vec<Arc<ImmutableDeserializedPacket>>) -> Option<Vec<usize>>,
     {
-        let mut retryable_packets = self.swap_priority_queue();
-        let retryable_packets: MinMaxHeap<Arc<ImmutableDeserializedPacket>> = retryable_packets
-            .drain_desc()
-            .chunks(batch_size)
-            .into_iter()
-            .flat_map(|packets_to_process| {
-                let packets_to_process = packets_to_process.into_iter().collect_vec();
-                if let Some(retryable_transaction_indexes) =
-                    processing_function(&packets_to_process)
-                {
-                    self.collect_retained_packets(
-                        &packets_to_process,
-                        &retryable_transaction_indexes,
-                    )
-                } else {
-                    packets_to_process
-                }
-            })
-            .collect::<MinMaxHeap<_>>();
-
-        self.unprocessed_packet_batches.packet_priority_queue = retryable_packets;
-
-        // Assert unprocessed queue is still consistent
-        assert_eq!(
-            self.unprocessed_packet_batches.packet_priority_queue.len(),
-            self.unprocessed_packet_batches
-                .message_hash_to_transaction
-                .len()
+        let mut retryable_packets = self.take_priority_queue();
+        let original_capacity = retryable_packets.capacity();
+        let mut new_retryable_packets = MinMaxHeap::with_capacity(original_capacity);
+        new_retryable_packets.extend(
+            retryable_packets
+                .drain_desc()
+                .chunks(batch_size)
+                .into_iter()
+                .flat_map(|packets_to_process| {
+                    let packets_to_process = packets_to_process.into_iter().collect_vec();
+                    if let Some(retryable_transaction_indexes) =
+                        processing_function(&packets_to_process)
+                    {
+                        self.collect_retained_packets(
+                            &packets_to_process,
+                            &retryable_transaction_indexes,
+                        )
+                    } else {
+                        packets_to_process
+                    }
+                }),
         );
+
+        self.unprocessed_packet_batches.packet_priority_queue = new_retryable_packets;
+        self.verify_priority_queue(original_capacity);
     }
 }