From 6e474307323105d7bef3ebe9d7f3fa1633bd1965 Mon Sep 17 00:00:00 2001
From: Theo Butler <theodusbutler@gmail.com>
Date: Mon, 27 Nov 2023 17:06:53 -0500
Subject: [PATCH] fix: avoid retaining uncled blocks in cache

---
 graph-gateway/src/chains/mod.rs | 10 ++++++++--
 prelude/src/epoch_cache.rs      |  7 +++++++
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/graph-gateway/src/chains/mod.rs b/graph-gateway/src/chains/mod.rs
index f0af1dc2..0842aa32 100644
--- a/graph-gateway/src/chains/mod.rs
+++ b/graph-gateway/src/chains/mod.rs
@@ -187,11 +187,17 @@ impl Actor {
             }
         }
 
-        self.handle_block(head.block.clone()).await;
-
         let blocks_per_minute = self.block_rate_estimator.update(head.block.number);
         self.blocks_per_minute_tx.write(blocks_per_minute);
 
+        // Remove prior blocks from the past minute. This avoids retaining uncled blocks that are
+        // frequently used.
+        let cutoff = head.block.number - blocks_per_minute;
+        self.number_to_hash.retain(|n, _| *n < cutoff);
+        self.hash_to_number.retain(|_, n| *n < cutoff);
+
+        self.handle_block(head.block.clone()).await;
+
         with_metric(&METRICS.chain_head, &[&self.chain], |g| {
             g.set(head.block.number as i64)
         });
diff --git a/prelude/src/epoch_cache.rs b/prelude/src/epoch_cache.rs
index 1dbbc213..905be7a9 100644
--- a/prelude/src/epoch_cache.rs
+++ b/prelude/src/epoch_cache.rs
@@ -82,6 +82,13 @@ impl<K: Eq + Hash, V, const C: u8> EpochCache<K, V, C> {
             f(v);
         }
     }
+
+    pub fn retain<F>(&mut self, mut f: F)
+    where
+        F: FnMut(&K, &mut V) -> bool,
+    {
+        self.0.retain(|k, (v, _)| f(k, v));
+    }
 }
 
 #[cfg(test)]