Streaming Expressions in Apache Solr
The Structure Query Language (SQL) engine is built on top of Solr’s Streaming API or streaming expressions. Streaming expression provides a simple and powerful stream processing language for Solr cloud and Its support for parallel relational algebra and real-time map-reduce.
Distributed Joins: Streaming expressions are added to distributed joins.
- Inner Join
- Left Outer Join
- Hash Join
- Outer Hash Join
Example:
innerJoin(search(collection1, q=*:*, fl="fieldP, fieldQ, fieldR", ...),
 search(collection2, q=*:*, fl="fieldP, fieldM, fieldN", ...),
 on="fieldP=fieldP")
Rolling streaming expression: It is a group of  the common field value tuple.
Example:
rollup(search(collection1, qt="/export"
            q="*:*",
            fl="id,course,price",
            sort="course asc"),
      over="course"),
      count(*),
      max(price))
Facet streaming expression: It pushes down the computation using json.
Example: facet(intellipaat_courses,
           q="*:*",
           buckets="course",
           bucketSorts="count(*) desc",
           bucketSizeLimit=1000,
           count(*),
           sum(price),
           max(popularity))
There are many available functions.
- Continuous push streaming
- Continuous pull streaming
- Request/Response streaming
- MapReduce is shuffling aggregation
- Pushdown faceted aggregation
- Parallel relational algebra (distributed joins, intersections, unions, complements)
- Publish/subscribe messaging
- Distributed graph traversal
This blog will help you get a better understanding of Solr + Hadoop = Big Data Love