perf: replace string concatenation with arithmetic in DecimalType.serialize

benchmarks/decimal_serialize.py

@@ -0,0 +1,122 @@
+#!/usr/bin/env python
+# Copyright ScyllaDB, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""
+Benchmark for DecimalType.serialize digit-to-integer conversion.
+
+Compares:
+  1. String join approach: int(''.join([str(d) for d in digits]))
+  2. Arithmetic loop: reduce via multiply-and-add
+
+Run with: python benchmarks/decimal_serialize.py
+"""
+
+import sys
+import time
+from decimal import Decimal
+
+sys.path.insert(0, ".")
+
+from cassandra.cqltypes import DecimalType
+
+
+# --- isolated digit-conversion benchmarks ---
+
+
+def digits_via_string(digits):
+    return int("".join([str(d) for d in digits]))
+
+
+def digits_via_arithmetic(digits):
+    n = 0
+    for d in digits:
+        n = n * 10 + d
+    return n
+
+
+def benchmark_digit_conversion(label, func, digits, iterations):
+    start = time.perf_counter()
+    for _ in range(iterations):
+        func(digits)
+    elapsed = time.perf_counter() - start
+    us = elapsed / iterations * 1_000_000
+    print(
+        f"  {label:30s}: {us:8.3f} us/call  ({iterations} iterations, {elapsed:.3f}s total)"
+    )
+    return elapsed
+
+
+def benchmark_full_serialize(label, dec_values, iterations):
+    proto = 4
+    start = time.perf_counter()
+    for _ in range(iterations):
+        for v in dec_values:
+            DecimalType.serialize(v, proto)
+    elapsed = time.perf_counter() - start
+    calls = iterations * len(dec_values)
+    us = elapsed / calls * 1_000_000
+    print(f"  {label:30s}: {us:8.3f} us/call  ({calls} calls, {elapsed:.3f}s total)")
+    return elapsed
+
+
+def main():
+    print("=" * 70)
+    print("DecimalType serialize benchmark")
+    print("=" * 70)
+
+    test_cases = [
+        ("small (3 digits)", Decimal("3.14")),
+        ("medium (10 digits)", Decimal("1234567890.0123456789")),
+        ("large (30 digits)", Decimal("1" * 30 + ".0")),
+    ]
+
+    iterations = 200_000
+
+    print()
+    print("--- Isolated digit-to-integer conversion ---")
+    for name, dec_val in test_cases:
+        sign, digits, exponent = dec_val.as_tuple()
+        print(f"\n  [{name}] {len(digits)} digits")
+        t_str = benchmark_digit_conversion(
+            "string join", digits_via_string, digits, iterations
+        )
+        t_arith = benchmark_digit_conversion(
+            "arithmetic loop", digits_via_arithmetic, digits, iterations
+        )
+        speedup = t_str / t_arith
+        print(f"  {'speedup':30s}: {speedup:.2f}x")
+
+    print()
+    print("--- Full DecimalType.serialize (current implementation) ---")
+    dec_values = [tc[1] for tc in test_cases]
+    benchmark_full_serialize("serialize (all sizes)", dec_values, iterations // 3)
+
+    # Round-trip correctness check
+    print()
+    print("--- Correctness check ---")
+    proto = 4
+    for name, dec_val in test_cases:
+        serialized = DecimalType.serialize(dec_val, proto)
+        deserialized = DecimalType.deserialize(serialized, proto)
+        ok = deserialized == dec_val
+        print(
+            f"  {name:30s}: {'PASS' if ok else 'FAIL'}  ({dec_val} -> {deserialized})"
+        )
+
+    print()
+
+
+if __name__ == "__main__":
+    main()

cassandra/cqltypes.py

@@ -440,7 +440,9 @@ def serialize(dec, protocol_version):
                 sign, digits, exponent = Decimal(dec).as_tuple()
             except Exception:
                 raise TypeError("Invalid type for Decimal value: %r", dec)
-        unscaled = int(''.join([str(digit) for digit in digits]))
+        unscaled = 0
+        for digit in digits:
+            unscaled = unscaled * 10 + digit
         if sign:
             unscaled *= -1
         scale = int32_pack(-exponent)