LWLock contention benchmarks in Postgres 18

Measure performance impact from LWLock contention in PostgreSQL 18 as a function of table index count and the max_locks_per_transaction parameter in a synthetic benchmark.

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Acceptance Criteria

• Benchmark measures LWLock contention in PostgreSQL 18 as a function of table index count and max_locks_per_transaction
• Test matrix covers multiple index counts (e.g., 0, 10, 50, 100 indexes per table) and max_locks_per_transaction values
• Metrics collected: TPS, latency, wait event distribution, lock contention time
• Synthetic workload is documented and reproducible

Definition of Done

• Benchmark scripts are committed and reproducible
• Results are documented with charts showing contention vs. index count and max_locks_per_transaction
• Findings include actionable recommendations for tuning