(improvement) Add __slots__ to _Frame to eliminate per-instance __dict__ (30-40ns saving, 264 bytes saved per call)

[mykaul]

Summary

Add __slots__ to the _Frame class in cassandra/connection.py. Eliminates per-instance __dict__ allocation.

Motivation

_Frame is instantiated for every response frame received from the server. It has exactly 6 fixed attributes (version, flags, stream, opcode, body_offset, end_pos) and is never monkey-patched or dynamically extended. Adding __slots__ removes the per-instance __dict__, reducing memory pressure on high-throughput workloads.

Benchmark (CPython 3.14, per-call)

Memory:

	Size
Original (obj + __dict__)	48 + 296 = 344 bytes
Optimized (__slots__)	80 bytes
Savings per frame	264 bytes (76.7%)

Timing:

Operation	Original	Optimized	Savings per call
Construction	146ns	118ns	28ns (19%)
Attribute access (4 attrs)	78ns	40ns	38ns (49%)

Bulk (10K frames):

• 1,285,888 → 885,120 bytes = 400KB saved (31%)
• At 1K concurrent in-flight frames: ~257KB saved, reducing GC pressure

Changes

• cassandra/connection.py: Add __slots__ = ('version', 'flags', 'stream', 'opcode', 'body_offset', 'end_pos') to _Frame

Testing

Unit tests pass (28/28 in test_connection.py). Verified that _Frame instances no longer have __dict__.

[mykaul]

Benchmark results (CPython 3.14, 500k iterations)

Per-instance memory:

	Size
Original (obj + __dict__)	48 + 296 = 344 bytes
Optimized (__slots__)	80 bytes
Savings per frame	264 bytes (76.7%)

Per-call timing:

Operation	Original	Optimized	Δ per call
Construction	146ns	118ns	-28ns
Attribute access (4 attrs)	78ns	40ns	-38ns

Bulk allocation (10k frames):

• Original: 1,285,888 bytes → Optimized: 885,120 bytes → 400KB saved (31%)
• At 1K concurrent in-flight frames: ~257KB saved, reducing GC pressure

_Frame has exactly 6 fixed attributes and is never dynamically extended — textbook __slots__ candidate.