From 350460f44c749f8d6d3ca8aabe9886f0c9be75f6 Mon Sep 17 00:00:00 2001
From: refcell <abigger87@gmail.com>
Date: Tue, 24 Sep 2024 21:21:42 -0400
Subject: [PATCH] feat(derive): holocene channel bank checks

---
 crates/derive/src/metrics.rs             |  8 ++++++++
 crates/derive/src/stages/channel_bank.rs | 24 +++++++++++++++++++-----
 2 files changed, 27 insertions(+), 5 deletions(-)

diff --git a/crates/derive/src/metrics.rs b/crates/derive/src/metrics.rs
index 589642f19..3f9d4b943 100644
--- a/crates/derive/src/metrics.rs
+++ b/crates/derive/src/metrics.rs
@@ -48,6 +48,14 @@ lazy_static! {
         &["error"]
     ).expect("Batch Reader Errors failed to register");
 
+    /// Tracks the number of times the channel queue was detected
+    /// non-empty during a frame ingestion, and new channel creation
+    /// was attempted post-holocene.
+    pub static ref CHANNEL_QUEUE_NON_EMPTY: IntGauge = register_int_gauge!(
+        "kona_derive_channel_queue_non_empty",
+        "Number of times a channel was attempted to be created in the channel bank, but the queue is non-empty post-holocene."
+    ).expect("Channel Queue Non Empty failed to register");
+
     /// Tracks the compression ratio of batches.
     pub static ref BATCH_COMPRESSION_RATIO: IntGauge = register_int_gauge!(
         "kona_derive_batch_compression_ratio",
diff --git a/crates/derive/src/stages/channel_bank.rs b/crates/derive/src/stages/channel_bank.rs
index a9a5d24bc..82c699d2c 100644
--- a/crates/derive/src/stages/channel_bank.rs
+++ b/crates/derive/src/stages/channel_bank.rs
@@ -83,11 +83,25 @@ where
         let origin = self.origin().ok_or(PipelineError::MissingOrigin.crit())?;
 
         // Get the channel for the frame, or create a new one if it doesn't exist.
-        let current_channel = self.channels.entry(frame.id).or_insert_with(|| {
-            let channel = Channel::new(frame.id, origin);
-            self.channel_queue.push_back(frame.id);
-            channel
-        });
+        let current_channel = match self.channels.get_mut(&frame.id) {
+            Some(c) => c,
+            None => {
+                if self.cfg.is_holocene_active(origin.timestamp) && !self.channel_queue.is_empty() {
+                    // In holocene, channels are strictly ordered.
+                    // If the previous frame is not the last in the channel
+                    // and a starting frame for the next channel arrives,
+                    // the previous channel/frames are removed and a new channel is created.
+                    self.channel_queue.clear();
+
+                    trace!(target: "channel-bank", "[holocene active] clearing non-empty channel queue");
+                    crate::inc!(CHANNEL_QUEUE_NON_EMPTY);
+                }
+                let channel = Channel::new(frame.id, origin);
+                self.channel_queue.push_back(frame.id);
+                self.channels.insert(frame.id, channel);
+                self.channels.get_mut(&frame.id).expect("Channel must be in queue")
+            }
+        };
 
         // Check if the channel is not timed out. If it has, ignore the frame.
         if current_channel.open_block_number() + self.cfg.channel_timeout(origin.timestamp) <