Struct FooterCount 

pub struct FooterCount<F> { /* private fields */ }

A dataset’s row count from its footers, each read once.

It starts from the footers the open already read — the two ends, or a sample — and reads only the rest. Once every file’s footer is in, the whole set is handed back once, for the shape cache, so a reopen reads none.

Implementations

impl<F: Clone> FooterCount<F>

pub fn new( files: usize, counted: Vec<usize>, known: impl IntoIterator<Item = (usize, Option<F>)>, ) -> Self

A count of counted among files files, starting from the footers known already holds, given as each one’s index.

pub fn count( &self, read: impl FnOnce(&[usize]) -> Option<Vec<Option<F>>>, row_groups: impl Fn(&F) -> Vec<usize>, ) -> Option<Counted<F>>

Count, reading the footers not yet in with read, which answers in the order it is asked, or None when the reads were abandoned. One that would not read before is tried again: a read can fail for a moment’s trouble as well as a broken file. Holds the footers while it reads, so two counts at once do not both read the same ones.