Dennis Gove created SOLR-8188:
---------------------------------
Summary: Add hash style joins to the Streaming API and Streaming
Expressions
Key: SOLR-8188
URL: https://issues.apache.org/jira/browse/SOLR-8188
Project: Solr
Issue Type: Improvement
Components: SolrJ
Reporter: Dennis Gove
Priority: Minor
Add HashJoinStream and OuterHashJoinStream to the Streaming API to allow for
optimized joining between sub-streams.
HashJoinStream is similar to an InnerJoinStream except that it does not insist
on any particular order and will read all values from the stream being hashed
(hashStream) when open() is called. During read() it will return the next tuple
from the stream not being hashed (fullStream) which has at least one matching
record in hashStream. It will return a tuple which is the merge of both tuples.
If the tuple from the fullStream matches with more than one tuple from the
hashStream then calling read() will return the merge with the next matching
tuple. The order of the resulting stream is the order of the fullStream.
OuterHashJoinStream is similar to a HashJoinStream and LeftOuterJoinStream in
that a tuple from fullStream will be returned even if it doesn't have a
matching record in hashStream. All other pieces are identical.
In expression form
{code}
hashJoin(
search(collection1, q=*:*, fl="fieldA, fieldB, fieldC", ...),
hashed=search(collection2, q=*:*, fl="fieldA, fieldB, fieldE", ...),
on="fieldA, fieldB"
)
{code}
{code}
outerHashJoin(
search(collection1, q=*:*, fl="fieldA, fieldB, fieldC", ...),
hashed=search(collection2, q=*:*, fl="fieldA, fieldB, fieldE", ...),
on="fieldA, fieldB"
)
{code}
As you can see the hashStream is named parameter which makes it very clear
which stream should be hashed.
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