Struct dataflow_types::plan::AvailableCollections [−][src]
pub struct AvailableCollections {
pub raw: bool,
pub arranged: Vec<(Vec<MirScalarExpr>, HashMap<usize, usize>, Vec<usize>)>,
}
Expand description
The forms in which an operator’s output is available;
it can be considered the plan-time equivalent of
render::context::CollectionBundle
.
These forms are either “raw”, representing an unarranged collection, or “arranged”, representing one that has been arranged by some key.
The raw collection, if it exists, may be consumed directly.
The arranged collections are slightly more complicated:
Each key here is attached to a description of how the corresponding
arrangement is permuted to remove value columns
that are redundant with key columns. Thus, the first element in each
tuple of arranged
is the arrangement key; the second is the map of
logical output columns to columns in the key or value of the deduplicated
representation, and the third is a “thinning expression”,
or list of columns to include in the value
when arranging.
For example, assume a 5-column collection is to be arranged by the key
[Column(2), Column(0) + Column(3), Column(1)]
.
Then Column(1)
and Column(2)
in the value are redundant with the key, and
only columns 0, 3, and 4 need to be stored separately.
The thinning expression will then be [0, 3, 4]
.
The permutation represents how to recover the
original values (logically [Column(0), Column(1), Column(2), Column(3), Column(4)]
)
from the key and value of the arrangement, logically
[Column(2), Column(0) + Column(3), Column(1), Column(0), Column(3), Column(4)]
.
Thus, the permutation in this case should be {0: 3, 1: 2, 2: 0, 3: 4, 4: 5}
.
Note that this description, while true at the time of writing, is merely illustrative;
users of this struct should not rely on the exact strategy used for generating
the permutations. As long as clients apply the thinning expression
when creating arrangements, and permute by the hashmap when reading them,
the contract of the function where they are generated (expr::permutation_for_arrangement
)
ensures that the correct values will be read.
Fields
raw: bool
Whether the collection exists in unarranged form.
arranged: Vec<(Vec<MirScalarExpr>, HashMap<usize, usize>, Vec<usize>)>
The set of arrangements of the collection, along with a column permutation mapping
Implementations
Represent a collection that is arranged in the specified ways.
Trait Implementations
Returns the “default value” for a type. Read more
fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error> where
__D: Deserializer<'de>,
fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error> where
__D: Deserializer<'de>,
Deserialize this value from the given Serde deserializer. Read more
This method tests for self
and other
values to be equal, and is used
by ==
. Read more
This method tests for !=
.
Auto Trait Implementations
impl RefUnwindSafe for AvailableCollections
impl Send for AvailableCollections
impl Sync for AvailableCollections
impl Unpin for AvailableCollections
impl UnwindSafe for AvailableCollections
Blanket Implementations
Mutably borrows from an owned value. Read more
Compare self to key
and return true
if they are equal.
Attaches the provided Subscriber
to this type, returning a
WithDispatch
wrapper. Read more
Attaches the current default Subscriber
to this type, returning a
WithDispatch
wrapper. Read more