From e328c9a6e0349344f585b830fc8b966318496adb Mon Sep 17 00:00:00 2001
From: Michael Hauser-Raspe <michael.hauser-raspe@cantab.net>
Date: Wed, 4 Mar 2026 11:55:32 +0000
Subject: [PATCH 1/3] fix: exclude primary when there are no replicas.

In that case we _don't_ want to exclude the primary.
---
 pgdog/src/backend/pool/lb/mod.rs  |  3 ++-
 pgdog/src/backend/pool/lb/test.rs | 36 +++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/pgdog/src/backend/pool/lb/mod.rs b/pgdog/src/backend/pool/lb/mod.rs
index 784f192e..21b30f36 100644
--- a/pgdog/src/backend/pool/lb/mod.rs
+++ b/pgdog/src/backend/pool/lb/mod.rs
@@ -277,7 +277,8 @@ impl LoadBalancer {
         let primary_reads = match self.rw_split {
             IncludePrimary => true,
             IncludePrimaryIfReplicaBanned => candidates.iter().any(|target| target.ban.banned()),
-            ExcludePrimary => false,
+            // we read from the primary if we have no replicas
+            ExcludePrimary => !candidates.iter().any(|target| target.role() == Role::Replica),
         };
 
         if !primary_reads {
diff --git a/pgdog/src/backend/pool/lb/test.rs b/pgdog/src/backend/pool/lb/test.rs
index 31d29a48..2f3f60dd 100644
--- a/pgdog/src/backend/pool/lb/test.rs
+++ b/pgdog/src/backend/pool/lb/test.rs
@@ -393,6 +393,42 @@ async fn test_read_write_split_include_primary() {
     replicas.shutdown();
 }
 
+#[tokio::test]
+async fn test_read_write_split_exclude_primary_no_replicas() {
+    let primary_config = create_test_pool_config("127.0.0.1", 5432);
+    let primary_pool = Pool::new(&primary_config);
+    primary_pool.launch();
+
+    let replica_configs = [];
+
+    let replicas = LoadBalancer::new(
+        &Some(primary_pool),
+        &replica_configs,
+        LoadBalancingStrategy::RoundRobin,
+        ReadWriteSplit::ExcludePrimary,
+    );
+    replicas.launch();
+
+    let request = Request::default();
+
+    // Try getting connections multiple times and we have primary in the set
+    let mut used_pool_ids = HashSet::new();
+    for _ in 0..2 {
+        let conn = replicas.get(&request).await.unwrap();
+        used_pool_ids.insert(conn.pool.id());
+    }
+
+    // Should use only primary
+    assert_eq!(used_pool_ids.len(), 1);
+
+    // Verify primary pool ID is in the set of used pools
+    let primary_id = replicas.primary().unwrap().id();
+    assert!(used_pool_ids.contains(&primary_id));
+
+    // Shutdown 
+    replicas.shutdown();
+}
+
 #[tokio::test]
 async fn test_read_write_split_exclude_primary_no_primary() {
     // Test exclude primary setting when no primary exists

From 353ba083713444055bc9754fae9e745c512f1092 Mon Sep 17 00:00:00 2001
From: Michael Hauser-Raspe <michael.hauser-raspe@cantab.net>
Date: Wed, 4 Mar 2026 11:55:54 +0000
Subject: [PATCH 2/3] One of our dependencies needs rust >= 1.91.

---
 mise.toml | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mise.toml b/mise.toml
index 0d2f0ed0..fe216b4a 100644
--- a/mise.toml
+++ b/mise.toml
@@ -1,3 +1,4 @@
 [tools]
+"rust" = { version = "1.91.0" }
 "cargo:cargo-nextest" = "latest"
 "cargo:cargo-watch" = "latest"
\ No newline at end of file

From 96c5ab182edfbfa99e376d4f9fdaf32cc18cc7e3 Mon Sep 17 00:00:00 2001
From: Michael Hauser-Raspe <michael.hauser-raspe@cantab.net>
Date: Wed, 4 Mar 2026 12:43:36 +0000
Subject: [PATCH 3/3] Cargo fmt.

---
 pgdog/src/backend/pool/lb/mod.rs  | 4 +++-
 pgdog/src/backend/pool/lb/test.rs | 2 +-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/pgdog/src/backend/pool/lb/mod.rs b/pgdog/src/backend/pool/lb/mod.rs
index 21b30f36..be9f6591 100644
--- a/pgdog/src/backend/pool/lb/mod.rs
+++ b/pgdog/src/backend/pool/lb/mod.rs
@@ -278,7 +278,9 @@ impl LoadBalancer {
             IncludePrimary => true,
             IncludePrimaryIfReplicaBanned => candidates.iter().any(|target| target.ban.banned()),
             // we read from the primary if we have no replicas
-            ExcludePrimary => !candidates.iter().any(|target| target.role() == Role::Replica),
+            ExcludePrimary => !candidates
+                .iter()
+                .any(|target| target.role() == Role::Replica),
         };
 
         if !primary_reads {
diff --git a/pgdog/src/backend/pool/lb/test.rs b/pgdog/src/backend/pool/lb/test.rs
index 2f3f60dd..0a32c1ae 100644
--- a/pgdog/src/backend/pool/lb/test.rs
+++ b/pgdog/src/backend/pool/lb/test.rs
@@ -425,7 +425,7 @@ async fn test_read_write_split_exclude_primary_no_replicas() {
     let primary_id = replicas.primary().unwrap().id();
     assert!(used_pool_ids.contains(&primary_id));
 
-    // Shutdown 
+    // Shutdown
     replicas.shutdown();
 }