From 917a76ecb4b1cb6742f810226d1ca0e26c461f75 Mon Sep 17 00:00:00 2001
From: Yaniv Michael Kaul <yaniv.kaul@scylladb.com>
Date: Mon, 6 Apr 2026 21:40:34 +0300
Subject: [PATCH] perf: optimize _key_parts_packed to avoid format string
 allocation

Replace per-call struct.pack(">H%dsB" % l, l, p, 0) with pre-compiled
uint16_pack(len(p)) + p + b'\\x00'. This eliminates the format string
interpolation and dynamic struct format creation on every call, using
the pre-compiled uint16_pack (struct.Struct('>H').pack) instead.

The routing key computation is called for every query when
TokenAwarePolicy is in use, making this a hot path.
---
 cassandra/query.py | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/cassandra/query.py b/cassandra/query.py
index 6c6878fdb4..8ef7b7fb64 100644
--- a/cassandra/query.py
+++ b/cassandra/query.py
@@ -23,6 +23,8 @@
 import re
 import struct
 import time
+
+from cassandra.marshal import uint16_pack
 import warnings
 
 from cassandra import ConsistencyLevel, OperationTimedOut
@@ -299,9 +301,9 @@ def __init__(self, retry_policy=None, consistency_level=None, routing_key=None,
         self.is_idempotent = is_idempotent
 
     def _key_parts_packed(self, parts):
+        _pack = uint16_pack
         for p in parts:
-            l = len(p)
-            yield struct.pack(">H%dsB" % l, l, p, 0)
+            yield _pack(len(p)) + p + b'\x00'
 
     def _get_routing_key(self):
         return self._routing_key