From a57d906cd274d18c96046c8c8019f06f069f01eb Mon Sep 17 00:00:00 2001
From: Romain Ruetschi <106849+romac@users.noreply.github.com>
Date: Tue, 22 Aug 2023 15:41:36 +0200
Subject: [PATCH 1/2] Do not perform client update if consensus state already
 exists

On some chains there are a few active channels using the same connection
and therefore clients. This PR adds a check in the client update code and
not create the message if the consensus state at desired height is already present.
This helps with reducing relayer fees, state bloating, etc by eliminating redundant updates.
---
 crates/relayer/src/foreign_client.rs | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/crates/relayer/src/foreign_client.rs b/crates/relayer/src/foreign_client.rs
index 008737e052..483e021bec 100644
--- a/crates/relayer/src/foreign_client.rs
+++ b/crates/relayer/src/foreign_client.rs
@@ -1069,6 +1069,24 @@ impl<DstChain: ChainHandle, SrcChain: ChainHandle> ForeignClient<DstChain, SrcCh
             }
         );
 
+        let consensus_state = self.dst_chain().query_consensus_state(
+            QueryConsensusStateRequest {
+                client_id: self.id().clone(),
+                consensus_height: target_height,
+                query_height: QueryHeight::Latest,
+            },
+            IncludeProof::No,
+        );
+
+        if let Ok((consensus_state, _)) = consensus_state {
+            debug!("consensus state already exists at height {target_height}, skipping update");
+            trace!(?consensus_state, "consensus state");
+
+            // If the client already stores a consensus state for the target height,
+            // there is no need to update the client
+            return Ok(vec![]);
+        }
+
         let src_application_latest_height = || {
             self.src_chain().query_latest_height().map_err(|e| {
                 ForeignClientError::client_create(
@@ -1087,6 +1105,7 @@ impl<DstChain: ChainHandle, SrcChain: ChainHandle> ForeignClient<DstChain, SrcCh
                     "dst_chain": self.dst_chain().id(),
                 }
             );
+
             // Wait for the source network to produce block(s) & reach `target_height`.
             while src_application_latest_height()? < target_height {
                 thread::sleep(Duration::from_millis(100));

From 306da4323df07cb9ab849a1a69d2914a4643349a Mon Sep 17 00:00:00 2001
From: Romain Ruetschi <106849+romac@users.noreply.github.com>
Date: Tue, 22 Aug 2023 16:36:57 +0200
Subject: [PATCH 2/2] Improve error message in `update client` command

---
 crates/relayer/src/foreign_client.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/crates/relayer/src/foreign_client.rs b/crates/relayer/src/foreign_client.rs
index 483e021bec..0db0b17051 100644
--- a/crates/relayer/src/foreign_client.rs
+++ b/crates/relayer/src/foreign_client.rs
@@ -107,7 +107,7 @@ define_error! {
                 height: Height,
             }
             |e| {
-                format_args!("client {} is already up-to-date with chain {}@{}",
+                format_args!("client {} is already up-to-date with chain {} at height {}",
                     e.client_id, e.chain_id, e.height)
             },