link:../src/crux/db.clj[role=include]This document serves as a guide for understand the query internals of Crux.
Crux has the fundamental notion of an index.
link:../src/crux/db.clj[role=include]The two operations are seek and next.
The layered index exists to facilitate the idea of navigating up and down an index, in a tree like manner.
link:../src/crux/db.clj[role=include]For example the index attribute+value+entity+content-hash is the following tree:
digraph G
{
attribute->value
value->entity
entity->content
}
open-level gives instructions to open and move down a level. In the
above example if could be moving the index down to point at the values
within a given attribute. That is to say that if we have an attribute
:name, the index will iterate across all values for that attribute,
until there are no more name values.
close-level moves the index back-up, so in the above example, we can
iterate at the higher level of attribute.
A Virtual Index comprises together multiple child indices. This is to join indices together, returning key/value pairs on where they match.
A join condition in a query could be reflected by a Virtual Index. A Virtual Index will maintain state as to where Index is currently positioned.
UnaryJoinVirtualIndex comprises of multiple child indices and
implements both Index and LayeredIndex. Calling seek-values on
it will advance all the child indices internally until they all
contain the same key. This involves calling seek-values on each
child index until the indices match at the same level. Calling
next-values would move all the indices along until the next common
key that all the indices share.
| 0 | 1 | 3 | 4 | 5 | 6 | |
| 0 | 2 | 3 | 5 | |||
| 2 | 3 | 4 | 5 | 6 |
In the above example, where UnaryJoinVirtualIndex joins three
RelationVirtualIndexs (a,b,c). Calling seek-values would return 3
as the first value found.
Calling next-values would jump ahead to the value 5.
TODO: JP: I need to understand the Nary vs Unary testing index-test.
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