Struct mz_transform::notice::IndexKeyEmpty

pub struct IndexKeyEmpty;

An index with an empty key is maximally skewed (all of the data goes to a single worker), and is almost never really useful. It’s slightly useful for a cross join, because a cross join also has an empty key, so we avoid rearranging the input. However, this is still not very useful, because

• Rearranging the input shouldn’t take too much memory, because if a cross join has a big input, then we have a serious problem anyway.
• Even with the arrangement already there, the cross join will read every input record, so the orders of magnitude performance improvements that can happen with other joins when an input arrangement exists can’t happen with a cross join. Also note that skew is hard to debug, so it’s good to avoid this problem in the first place.

Trait Implementations

impl Clone for IndexKeyEmpty

fn clone(&self) -> IndexKeyEmpty

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for IndexKeyEmpty

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

Formats the value using the given formatter.

impl From<IndexKeyEmpty> for RawOptimizerNotice

fn from(value: IndexKeyEmpty) -> Self

Converts to this type from the input type.

impl Hash for IndexKeyEmpty

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl OptimizerNoticeApi for IndexKeyEmpty

fn dependencies(&self) -> BTreeSet<GlobalId>

See OptimizerNoticeApi::dependencies.

fn fmt_message( &self, f: &mut Formatter<'_>, _humanizer: &dyn ExprHumanizer, _redacted: bool, ) -> Result

Format the text for the optionally redacted OptimizerNotice::message value for this notice.

fn fmt_hint( &self, f: &mut Formatter<'_>, _humanizer: &dyn ExprHumanizer, _redacted: bool, ) -> Result

Format the text for the optionally redacted OptimizerNotice::hint value for this notice.

fn fmt_action( &self, f: &mut Formatter<'_>, _humanizer: &dyn ExprHumanizer, _redacted: bool, ) -> Result

Format the text for the optionally redacted OptimizerNotice::action value for this notice.

fn action_kind(&self, _humanizer: &dyn ExprHumanizer) -> ActionKind

The kind of action suggested by this notice.

fn message<'a>( &'a self, humanizer: &'a dyn ExprHumanizer, redacted: bool, ) -> HumanizedMessage<'a, Self>

Return a thunk that will render the optionally redacted OptimizerNotice::message value for this notice.

fn hint<'a>( &'a self, humanizer: &'a dyn ExprHumanizer, redacted: bool, ) -> HumanizedHint<'a, Self>

Return a thunk that will render the optionally redacted OptimizerNotice::hint value for this notice.

fn action<'a>( &'a self, humanizer: &'a dyn ExprHumanizer, redacted: bool, ) -> HumanizedAction<'a, Self>

Return a thunk that will render the optionally redacted OptimizerNotice::action value for this notice.

impl PartialEq for IndexKeyEmpty

fn eq(&self, other: &IndexKeyEmpty) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Eq for IndexKeyEmpty

impl StructuralPartialEq for IndexKeyEmpty