Type Alias JoinHashMap

pub type JoinHashMap<K> = HashMap<K, RowId, PrecomputedBuildHasher, MonitoredGlobalAlloc>;

In JoinHashMap, we only save the row id of the first build row that has the hash key. In fact, in the build side there may be multiple rows with the same hash key. To handle this case, we use ChunkedData to link them together. For example:

id	key	row
0	1	(1, 2, 3)
1	4	(4, 5, 6)
2	1	(1, 3, 7)
3	1	(1, 3, 2)
4	3	(3, 2, 1)

The corresponding join hash map is:

key	value
1	0
4	1
3	4

And we save build rows with the same key like this:

id	value
0	2
1	None
2	3
3	None
4	None

This can be seen as an implicit linked list. For convenience, we use RowIdIter to iterate all build side row ids with the given key.

Aliased Type

struct JoinHashMap<K> { /* private fields */ }