Function recommend 

pub fn recommend(
    health: &TableHealth,
    threshold_vacuum: f64,
    threshold_partition_rows: i64,
) -> Recommendation

Pure recommendation function for a single table.

Determinism

recommend takes only the borrowed TableHealth and two scalar thresholds. It performs no I/O, reads no globals, allocates only the String inside PartitionRecommended::reason (when that arm fires), and traverses no unordered collections. Repeated invocation on byte-identical inputs returns byte-identical outputs — the recommend_is_deterministic test asserts this with 100 repetitions.

Threshold semantics

• threshold_vacuum: dead-tuple ratio strictly above which Recommendation::VacuumNeeded fires. Typical: 0.2 (20% bloat). Higher values mean the operator tolerates more bloat before flagging.
• threshold_partition_rows: live row count strictly above which an unpartitioned table triggers Recommendation::PartitionRecommended. Typical: 10_000_000. The same threshold is reused for the per-partition row average that drives Recommendation::PartitionCountIncrease.

Edge cases

• Empty table (n_live_tup == 0 && n_dead_tup == 0): vacuum check is short-circuited (division-by-zero guard). Partition checks still run but neither fires for an empty table.
• partition_count == 0: treated as “not partitioned” — only the PartitionRecommended rule can fire.
• partition_count >= 1 but row count below threshold: falls through to Healthy.

See also

Recommendation for the precedence ordering.