Add Proposer Cache Pruning & POS Activated Banner (#3109)

## Issue Addressed

The proposers cache wasn't being pruned. Also didn't have a celebratory banner for the merge 😄

## Banner
![pos_log_panda](https://user-images.githubusercontent.com/37123614/159528545-3aa54cbd-9362-49b1-830c-f4402f6ac341.png)

beacon_node/beacon_chain/src/block_verification.rs

@@ -59,7 +59,7 @@ use fork_choice::{ForkChoice, ForkChoiceStore, PayloadVerificationStatus};
 use parking_lot::RwLockReadGuard;
 use proto_array::Block as ProtoBlock;
 use safe_arith::ArithError;
-use slog::{debug, error, Logger};
+use slog::{debug, error, info, Logger};
 use slot_clock::SlotClock;
 use ssz::Encode;
 use state_processing::per_block_processing::is_merge_transition_block;
@@ -81,6 +81,30 @@ use types::{
     SignedBeaconBlock, SignedBeaconBlockHeader, Slot,
 };
 
+const POS_PANDA_BANNER: &str = r#"
+    ,,,         ,,,                                               ,,,         ,,,
+  ;"   ^;     ;'   ",                                           ;"   ^;     ;'   ",
+  ;    s$$$$$$$s     ;                                          ;    s$$$$$$$s     ;
+  ,  ss$$$$$$$$$$s  ,'  ooooooooo.    .oooooo.   .oooooo..o     ,  ss$$$$$$$$$$s  ,'
+  ;s$$$$$$$$$$$$$$$     `888   `Y88. d8P'  `Y8b d8P'    `Y8     ;s$$$$$$$$$$$$$$$
+  $$$$$$$$$$$$$$$$$$     888   .d88'888      888Y88bo.          $$$$$$$$$$$$$$$$$$
+ $$$$P""Y$$$Y""W$$$$$    888ooo88P' 888      888 `"Y8888o.     $$$$P""Y$$$Y""W$$$$$
+ $$$$  p"$$$"q  $$$$$    888        888      888     `"Y88b    $$$$  p"$$$"q  $$$$$
+ $$$$  .$$$$$.  $$$$     888        `88b    d88'oo     .d8P    $$$$  .$$$$$.  $$$$
+  $$DcaU$$$$$$$$$$      o888o        `Y8bood8P' 8""88888P'      $$DcaU$$$$$$$$$$
+    "Y$$$"*"$$$Y"                                                 "Y$$$"*"$$$Y"
+        "$b.$$"                                                       "$b.$$"
+
+       .o.                   .   o8o                         .                 .o8
+      .888.                .o8   `"'                       .o8                "888
+     .8"888.     .ooooo. .o888oooooo oooo    ooo .oooo.  .o888oo .ooooo.  .oooo888
+    .8' `888.   d88' `"Y8  888  `888  `88.  .8' `P  )88b   888  d88' `88bd88' `888
+   .88ooo8888.  888        888   888   `88..8'   .oP"888   888  888ooo888888   888
+  .8'     `888. 888   .o8  888 . 888    `888'   d8(  888   888 .888    .o888   888
+ o88o     o8888o`Y8bod8P'  "888"o888o    `8'    `Y888""8o  "888"`Y8bod8P'`Y8bod88P"
+
+"#;
+
 /// Maximum block slot number. Block with slots bigger than this constant will NOT be processed.
 const MAXIMUM_BLOCK_SLOT_NUMBER: u64 = 4_294_967_296; // 2^32
 
@@ -1118,9 +1142,13 @@ impl<'a, T: BeaconChainTypes> FullyVerifiedBlock<'a, T> {
         //   early.
         // - Doing the check here means we can keep our fork-choice implementation "pure". I.e., no
         //   calls to remote servers.
+        let valid_merge_transition_block =
             if is_merge_transition_block(&state, block.message().body()) {
-            validate_merge_block(chain, block.message())?
+                validate_merge_block(chain, block.message())?;
-        }
+                true
+            } else {
+                false
+            };
 
         // The specification declares that this should be run *inside* `per_block_processing`,
         // however we run it here to keep `per_block_processing` pure (i.e., no calls to external
@@ -1264,6 +1292,14 @@ impl<'a, T: BeaconChainTypes> FullyVerifiedBlock<'a, T> {
             });
         }
 
+        if valid_merge_transition_block {
+            info!(chain.log, "{}", POS_PANDA_BANNER);
+            info!(chain.log, "Proof of Stake Activated"; "slot" => block.slot());
+            info!(chain.log, ""; "Terminal POW Block Hash" => ?block.message().execution_payload()?.parent_hash.into_root());
+            info!(chain.log, ""; "Merge Transition Block Root" => ?block.message().tree_hash_root());
+            info!(chain.log, ""; "Merge Transition Execution Hash" => ?block.message().execution_payload()?.block_hash.into_root());
+        }
+
         Ok(Self {
             block,
             block_root,

beacon_node/client/src/builder.rs

@@ -704,8 +704,7 @@ where
                     execution_layer.spawn_watchdog_routine(beacon_chain.slot_clock.clone());
 
                     // Spawn a routine that removes expired proposer preparations.
-                    execution_layer
+                    execution_layer.spawn_clean_proposer_caches_routine::<TSlotClock, TEthSpec>(
-                        .spawn_clean_proposer_preparation_routine::<TSlotClock, TEthSpec>(
                         beacon_chain.slot_clock.clone(),
                     );
 

beacon_node/execution_layer/src/lib.rs

@@ -374,8 +374,8 @@ impl ExecutionLayer {
         self.engines().upcheck_not_synced(Logging::Disabled).await;
     }
 
-    /// Spawns a routine which cleans the cached proposer preparations periodically.
+    /// Spawns a routine which cleans the cached proposer data periodically.
-    pub fn spawn_clean_proposer_preparation_routine<S: SlotClock + 'static, T: EthSpec>(
+    pub fn spawn_clean_proposer_caches_routine<S: SlotClock + 'static, T: EthSpec>(
         &self,
         slot_clock: S,
     ) {
@@ -393,7 +393,7 @@ impl ExecutionLayer {
                         .map(|slot| slot.epoch(T::slots_per_epoch()))
                     {
                         Some(current_epoch) => el
-                            .clean_proposer_preparation(current_epoch)
+                            .clean_proposer_caches::<T>(current_epoch)
                             .await
                             .map_err(|e| {
                                 error!(
@@ -473,8 +473,8 @@ impl ExecutionLayer {
         }
     }
 
-    /// Removes expired entries from cached proposer preparations
+    /// Removes expired entries from proposer_preparation_data and proposers caches
-    async fn clean_proposer_preparation(&self, current_epoch: Epoch) -> Result<(), Error> {
+    async fn clean_proposer_caches<T: EthSpec>(&self, current_epoch: Epoch) -> Result<(), Error> {
         let mut proposer_preparation_data = self.proposer_preparation_data().await;
 
         // Keep all entries that have been updated in the last 2 epochs
@@ -482,6 +482,13 @@ impl ExecutionLayer {
         proposer_preparation_data.retain(|_validator_index, preparation_entry| {
             preparation_entry.update_epoch >= retain_epoch
         });
+        drop(proposer_preparation_data);
+
+        let retain_slot = retain_epoch.start_slot(T::slots_per_epoch());
+        self.proposers()
+            .write()
+            .await
+            .retain(|proposer_key, _proposer| proposer_key.slot >= retain_slot);
 
         Ok(())
     }

beacon_node/http_api/src/lib.rs

@@ -954,7 +954,6 @@ pub fn serve<T: BeaconChainTypes>(
                         delay,
                     );
 
-
                     match chain.process_block(block.clone()) {
                         Ok(root) => {
                             info!(