Function partition_table 

pub async fn partition_table(
    tx: &mut Transaction<'_>,
    table: QualifiedTableRef<'_>,
    pk_col: &str,
    params: PartitionParams,
) -> Result<Vec<String>, MySqlError>

Computes up to num_workers - 1 partition boundaries that divide the primary key space into num_workers roughly even partitions. At most max_probed_prefixes prefixes are probed in MySQL to bound the time spent. Each prefix probe costs a few queries that should each be quick (index dives, instead of table scans).

Nothing here validates the setup: the caller must abide by these constraints or undefined/untested behavior could occur, e.g. boundaries that fail to partition the key space or a walk that does not converge.

• pk_col is the table’s single-column primary key.
• The column type is CHAR or VARCHAR with a declared length of at most crate::probe::MAX_KEY_LENGTH characters.
• The column collation is utf8mb4_bin.
• The transaction is REPEATABLE READ, so the probes (several queries each) all see one snapshot of the table.

min_split_threshold is the smallest estimated row count granularity partitioning will target, which means if the algorithm processes a prefix estimated to cover less than min_split_threshold rows it won’t bother splitting it up further. This is useful to avoid unnecessary work for smaller tables limiting the overhead of partitioning.