Function set_no_deferrable_on_read 

pub fn set_no_deferrable_on_read(value: bool)

Configure whether read transactions on Postgres should omit DEFERRABLE.

When true, Read::begin issues SET TRANSACTION ISOLATION LEVEL SERIALIZABLE, READ ONLY (no DEFERRABLE) so the transaction starts immediately rather than waiting for a safe serializable snapshot. Default: false. Call this once at startup based on the operator’s chosen configuration.