mz_compute::sink::correction_v2

Struct Cursor

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struct Cursor<D: Data> {
    chunks: VecDeque<Rc<Chunk<D>>>,
    chunk_offset: usize,
    limit: Option<usize>,
    overwrite_ts: Option<Timestamp>,
}
Expand description

A cursor over updates in a chain.

A cursor provides two guarantees:

  • Produced updates are ordered and consolidated.
  • A cursor always yields at least one update.

The second guarantee is enforced through the type system: Every method that steps a cursor forward consumes self and returns an Option<Cursor> that’s None if the operation stepped over the last update.

A cursor holds on to Rc<Chunk>s, allowing multiple cursors to produce updates from the same chunks concurrently. As soon as a cursor is done producing updates from a Chunk it drops its reference. Once the last cursor is done with a Chunk its memory can be reclaimed.

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§chunks: VecDeque<Rc<Chunk<D>>>

The chunks from which updates can still be produced.

§chunk_offset: usize

The current offset into chunks.front().

§limit: Option<usize>

An optional limit for the number of updates the cursor will produce.

§overwrite_ts: Option<Timestamp>

An optional overwrite for the timestamp of produced updates.

Implementations§

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impl<D: Data> Cursor<D>

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fn new(chunks: VecDeque<Rc<Chunk<D>>>) -> Option<Self>

Construct a cursor over a list of chunks.

Returns None if chunks is empty.

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fn set_limit(self, limit: usize) -> Option<Self>

Set a limit for the number of updates this cursor will produce.

§Panics

Panics if there is already a limit lower than the new one.

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fn get(&self) -> (&D, Timestamp, Diff)

Get a reference to the current update.

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fn get_chunk(&self) -> &Chunk<D>

Get a reference to the current chunk.

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fn step(self) -> Option<Self>

Step to the next update.

Returns the stepped cursor, or None if the step was over the last update.

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fn skip_chunk(self) -> Option<(Self, usize)>

Skip the remainder of the current chunk.

Returns the forwarded cursor and the number of updates skipped, or None if no chunks are left after the skip.

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fn skip_time(self, time: Timestamp) -> Option<(Self, usize)>

Skip all updates with times <= the given time.

Returns the forwarded cursor and the number of updates skipped, or None if no updates are left after the skip.

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fn advance_by(self, since_ts: Timestamp) -> Vec<Self>

Advance all updates in this cursor by the given since_ts.

Returns a list of cursors, each of which yields ordered and consolidated updates that have been advanced by since_ts.

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fn split_at_time(self, time: Timestamp) -> (Option<Self>, Option<Self>)

Split the cursor at the given time.

Returns two cursors, the first yielding all updates at times < time, the second yielding all updates at times >= time. Both can be None if they would be empty.

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fn try_unwrap(self) -> Result<Chain<D>, (&'static str, Self)>

Attempt to unwrap the cursor into a Chain.

This operation efficiently reuses chunks by directly inserting them into the output chain where possible.

An unwrap is only successful if the cursor’s limit and overwrite_ts are both None and the cursor has unique references to its chunks. If the unwrap fails, this method returns an Err containing the cursor in an unchanged state, allowing the caller to convert it into a chain by copying chunks rather than reusing them.

Trait Implementations§

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impl<D: Clone + Data> Clone for Cursor<D>

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fn clone(&self) -> Cursor<D>

Returns a copy of the value. Read more
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fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source. Read more
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impl<D: Debug + Data> Debug for Cursor<D>

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

Formats the value using the given formatter. Read more
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impl<D: Data> From<Cursor<D>> for Chain<D>

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fn from(cursor: Cursor<D>) -> Self

Converts to this type from the input type.
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impl<D: Data> FromIterator<Cursor<D>> for MergeHeap<D>

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fn from_iter<I: IntoIterator<Item = Cursor<D>>>(cursors: I) -> Self

Creates a value from an iterator. Read more

Auto Trait Implementations§

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impl<D> Freeze for Cursor<D>

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impl<D> RefUnwindSafe for Cursor<D>

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impl<D> !Send for Cursor<D>

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impl<D> !Sync for Cursor<D>

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impl<D> Unpin for Cursor<D>

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impl<D> UnwindSafe for Cursor<D>

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