Search through CQL

Executing OpenSearch queries through the Cassandra CQL driver lets applications reuse their existing Cassandra connectivity while still accessing Elassandra search features.

Benefits include:

  • no separate HTTP load balancer for simple driver-based search flows

  • shared Cassandra authentication and TLS handling

  • access to Cassandra paging together with search requests

Configuration

Enable the Elassandra query handler and add the query columns to the target table:

JVM_OPTS="$JVM_OPTS -Dcassandra.custom_query_handler_class=org.elassandra.index.ElasticQueryHandler"

ALTER TABLE twitter."_doc" ADD es_query text;
ALTER TABLE twitter."_doc" ADD es_options text;

Search request through CQL

Once enabled, search requests can be issued directly from CQL:

SELECT "_id", user, message
FROM twitter."_doc"
WHERE es_query='{"query":{"query_string":{"query":"message:dynamic"}}}';

If the target index name differs from the keyspace name, specify it in es_options and use ALLOW FILTERING:

SELECT "_id", user, message
FROM twitter."_doc"
WHERE es_query='{"query":{"term":{"user":"Poulpy"}}}'
  AND es_options='indices=twitter'
ALLOW FILTERING;

Paging

When Cassandra driver paging is enabled, Elassandra uses a search scroll internally for multi-page result sets. If you only need the first few hits, use LIMIT so the coordinator can keep the search request small:

SELECT "_id", user
FROM twitter."_doc"
WHERE es_query='{"query":{"match_all":{}}}'
LIMIT 10;

Routing

Because Elassandra maps search data onto Cassandra token ownership, routing decisions are based on the Cassandra primary key and partition key model. Keep that relationship in mind when designing ids and partitions for search-heavy tables.

CQL Functions

Applications that already consume Cassandra result metadata can also inspect the incoming payload returned by Elassandra to read search metadata such as total hits and shard status.

Elassandra aggregations through CQL

Aggregations can be executed through the same es_query mechanism. The aggregation response is returned through the query payload rather than regular CQL columns, which makes this mode best suited to application code rather than interactive shell use.

Application unit tests

For current application-level testing, prefer the repository Docker or Helm workflows and run CQL search queries against a real Elassandra node with org.elassandra.index.ElasticQueryHandler enabled.

CQL tracing

When troubleshooting search over CQL, enable Cassandra tracing to inspect the underlying row fetches and coordinator work:

tracing on;
SELECT "_id"
FROM twitter."_doc"
WHERE es_query='{"query":{"match_all":{}}}'
LIMIT 1;