(improvement) (python code path only): cache namedtuple class in named_tuple_factory to avoid …

[mykaul]

Cache the Row namedtuple class keyed on tuple(colnames) so Python's namedtuple() (which internally calls exec()) is only invoked once per unique column schema. For prepared statements the column names never change, eliminating redundant class creation on every result set.

Motivation

named_tuple_factory is the default row_factory in the driver. Every call to namedtuple('Row', columns) internally calls exec() to generate a new class -- this is surprisingly expensive. For prepared statements executing the same query repeatedly, the column names never change, yet we pay the namedtuple() + exec() cost on every result set.

Benchmark results

Benchmarks compare the original code (Before) against the new cached implementation (After). All timings in us (microseconds).

10 columns, 1 row (isolates class creation overhead):

Variant	Min (us)	Mean (us)	Median (us)	Ops/sec	Speedup
Before (original)	43.49	59.98	47.65	16,700	—
After (with cache)	0.24	0.45	0.35	2,210,000	~133x

5 columns, 100 rows:

Variant	Min (us)	Mean (us)	Median (us)	Ops/sec	Speedup
Before (original)	57.4	91.2	65.8	10,969	—
After (with cache)	19.3	25.3	24.0	39,594	~3.6x

10 columns, 100 rows:

Variant	Min (us)	Mean (us)	Median (us)	Ops/sec	Speedup
Before (original)	56.7	101.9	75.6	9,813	—
After (with cache)	18.1	21.4	20.4	46,825	~4.8x

Design notes

• Cache is a plain dict keyed on tuple(colnames) (raw column names before cleaning)
• Error handling paths (SyntaxError, Exception) preserved unchanged
• Cache is naturally bounded by the number of distinct queries

Tests

All existing unit tests pass (46 passed).

Pre-review checklist

• I have split my patch into logically separate commits.
• All commit messages clearly explain what they change and why.
• I added relevant tests for new features and bug fixes.
• All commits compile, pass static checks and pass test.
• PR description sums up the changes and reasons why they should be introduced.
• I have provided docstrings for the public items that I want to introduce.
• I have adjusted the documentation in ./docs/source/.
• I added appropriate Fixes: annotations to PR description.