Struct Places 

pub struct Places { /* private fields */ }

The per-part row count prefix sum of one table, built once at open.

Sixty four u32 per stripe plus a u64 per stripe, which for a hundred million rows is about four hundred kilobytes. Section 4.2 of spec/graph/04-in-memory.md says it is built at open rather than walked per lookup, and the reason is arithmetic rather than taste: a join gathers millions of times and an open happens once.

Implementations

impl Places

pub fn build(per_stripe: &[Vec<u32>]) -> Result<Self>

Builds the prefix sum from the per-part row counts of every stripe, in stripe order.

Errors

If a stripe holds more than STRIPE_PARTS parts, if a part is wider than PART_ROWS, if a part other than the last of its stripe is short, or if the total overflows a u64. Every one of those is a malformed directory rather than a usage error, and the reason they are checked here rather than trusted is that this structure is what a link join indexes with: a prefix sum that is wrong by one resolves every rid past the fault to the wrong row, and a wrong row is a wrong answer rather than a slow one.

pub fn rows(&self) -> u64

Committed rows, which is one past the largest resolvable rid.

pub fn bytes(&self) -> usize

Bytes this structure holds, for the cache budget of section 4.4.

pub fn place(&self, rid: Rid) -> Option<Place>

Resolves a rid to its physical position, or None when it is past the end of the table.

None rather than an error because a link may legitimately point past the end: a forward link built against one generation and read against another is stale, and section 3.1 of spec/graph/03-the-file-format.md wants a stale section ignored rather than raised. The generation check is what catches that case first; this is the second line.

pub fn rid(&self, place: Place) -> Option<Rid>

The rid of a physical position, which is Places::place backwards.

The forward link build needs this: it walks the parent table in physical order and has to record what each row’s rid is.

None when the position is not in the table.

pub fn stripe_rows(&self, stripe: u32) -> Option<u64>

Rows in one stripe, or None when there is no such stripe.

pub fn stripes(&self) -> usize

Stripes in the table.

Trait Implementations

impl Clone for Places

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Places

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.