From 0fd5208a03884fb04679800331edc451b5f0caaa Mon Sep 17 00:00:00 2001
From: "Kamat, Trivikram" <16024985+trivikr@users.noreply.github.com>
Date: Thu, 30 Apr 2026 20:40:11 -0700
Subject: [PATCH 1/3] perf: avoid redundant scans in BalancedPool dispatcher
 selection

Assisted-by: openai:gpt-5.5
Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com>
---
 lib/dispatcher/balanced-pool.js | 35 +++++++++++++++------------------
 1 file changed, 16 insertions(+), 19 deletions(-)

diff --git a/lib/dispatcher/balanced-pool.js b/lib/dispatcher/balanced-pool.js
index 8bad487b3f2..f0796b03e28 100644
--- a/lib/dispatcher/balanced-pool.js
+++ b/lib/dispatcher/balanced-pool.js
@@ -164,32 +164,25 @@ class BalancedPool extends PoolBase {
       throw new BalancedPoolMissingUpstreamError()
     }
 
-    const dispatcher = this[kClients].find(dispatcher => (
-      !dispatcher[kNeedDrain] &&
-      dispatcher.closed !== true &&
-      dispatcher.destroyed !== true
-    ))
-
-    if (!dispatcher) {
-      return
-    }
-
-    const allClientsBusy = this[kClients].map(pool => pool[kNeedDrain]).reduce((a, b) => a && b, true)
-
-    if (allClientsBusy) {
-      return
-    }
-
     let counter = 0
 
-    let maxWeightIndex = this[kClients].findIndex(pool => !pool[kNeedDrain])
+    let maxWeightIndex = -1
 
     while (counter++ < this[kClients].length) {
       this[kIndex] = (this[kIndex] + 1) % this[kClients].length
       const pool = this[kClients][this[kIndex]]
+      const available = (
+        !pool[kNeedDrain] &&
+        pool.closed !== true &&
+        pool.destroyed !== true
+      )
 
       // find pool index with the largest weight
-      if (pool[kWeight] > this[kClients][maxWeightIndex][kWeight] && !pool[kNeedDrain]) {
+      if (available && (
+        maxWeightIndex === -1 ||
+        pool[kWeight] > this[kClients][maxWeightIndex][kWeight] ||
+        (pool[kWeight] === this[kClients][maxWeightIndex][kWeight] && this[kIndex] < maxWeightIndex)
+      )) {
         maxWeightIndex = this[kIndex]
       }
 
@@ -202,11 +195,15 @@ class BalancedPool extends PoolBase {
           this[kCurrentWeight] = this[kMaxWeightPerServer]
         }
       }
-      if (pool[kWeight] >= this[kCurrentWeight] && (!pool[kNeedDrain])) {
+      if (available && pool[kWeight] >= this[kCurrentWeight]) {
         return pool
       }
     }
 
+    if (maxWeightIndex === -1) {
+      return
+    }
+
     this[kCurrentWeight] = this[kClients][maxWeightIndex][kWeight]
     this[kIndex] = maxWeightIndex
     return this[kClients][maxWeightIndex]

From 91b75bc33eee03dec1102cb764231d1d8288a563 Mon Sep 17 00:00:00 2001
From: "Kamat, Trivikram" <16024985+trivikr@users.noreply.github.com>
Date: Thu, 30 Apr 2026 21:02:23 -0700
Subject: [PATCH 2/3] chore: drop unnecessary BalancedPool equal-weight
 tie-breaker

---
 lib/dispatcher/balanced-pool.js | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/lib/dispatcher/balanced-pool.js b/lib/dispatcher/balanced-pool.js
index f0796b03e28..c3d22fa3263 100644
--- a/lib/dispatcher/balanced-pool.js
+++ b/lib/dispatcher/balanced-pool.js
@@ -180,8 +180,7 @@ class BalancedPool extends PoolBase {
       // find pool index with the largest weight
       if (available && (
         maxWeightIndex === -1 ||
-        pool[kWeight] > this[kClients][maxWeightIndex][kWeight] ||
-        (pool[kWeight] === this[kClients][maxWeightIndex][kWeight] && this[kIndex] < maxWeightIndex)
+        pool[kWeight] > this[kClients][maxWeightIndex][kWeight]
       )) {
         maxWeightIndex = this[kIndex]
       }

From dca2afc24b706083be3c80866bffd91d2a4b8485 Mon Sep 17 00:00:00 2001
From: "Kamat, Trivikram" <16024985+trivikr@users.noreply.github.com>
Date: Thu, 30 Apr 2026 22:14:46 -0700
Subject: [PATCH 3/3] chore: simplify BalancedPool availability checks

---
 lib/dispatcher/balanced-pool.js | 30 ++++++++++++++++--------------
 1 file changed, 16 insertions(+), 14 deletions(-)

diff --git a/lib/dispatcher/balanced-pool.js b/lib/dispatcher/balanced-pool.js
index c3d22fa3263..ca14bf6ed1d 100644
--- a/lib/dispatcher/balanced-pool.js
+++ b/lib/dispatcher/balanced-pool.js
@@ -171,19 +171,6 @@ class BalancedPool extends PoolBase {
     while (counter++ < this[kClients].length) {
       this[kIndex] = (this[kIndex] + 1) % this[kClients].length
       const pool = this[kClients][this[kIndex]]
-      const available = (
-        !pool[kNeedDrain] &&
-        pool.closed !== true &&
-        pool.destroyed !== true
-      )
-
-      // find pool index with the largest weight
-      if (available && (
-        maxWeightIndex === -1 ||
-        pool[kWeight] > this[kClients][maxWeightIndex][kWeight]
-      )) {
-        maxWeightIndex = this[kIndex]
-      }
 
       // decrease the current weight every `this[kClients].length`.
       if (this[kIndex] === 0) {
@@ -194,7 +181,22 @@ class BalancedPool extends PoolBase {
           this[kCurrentWeight] = this[kMaxWeightPerServer]
         }
       }
-      if (available && pool[kWeight] >= this[kCurrentWeight]) {
+
+      // Skip unavailable pools after updating the current weight for this cycle.
+      if (
+        pool[kNeedDrain] ||
+        pool.closed === true ||
+        pool.destroyed === true
+      ) {
+        continue
+      }
+
+      // Track the best fallback if no pool matches the current weight.
+      if (maxWeightIndex === -1 || pool[kWeight] > this[kClients][maxWeightIndex][kWeight]) {
+        maxWeightIndex = this[kIndex]
+      }
+
+      if (pool[kWeight] >= this[kCurrentWeight]) {
         return pool
       }
     }