Apache Solr Streaming Expressions

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 to messaging
• Distributed graph traversal