Apache Solr Reference Guide Covering Apache Solr 6.0

nction. When this expression is sent to the /stream handler, the /stream hander sees the daemon function
and keeps it in memory where it will run at intervals. In this particular example, the daemon function will run the u
pdate function every second. The update function is wrapping a topic function, which returns all new
documents for a specific query. The update function will send the new documents to another collection to be
indexed.
The effect of this is to continuously push new documents that match a specific query into another collection.
Custom push functions can be plugged in that push documents out of Solr and into other systems, such as Kafka
or an email system.
Push streaming can also be used for continuous background aggregation scenarios where aggregates are rolled
up in the background at intervals and pushed to other Solr collections. Another use case is continuous
background machine learning model optimization, where the optimized model is pushed to another Solr
collection where they can be integrated into queries.
The /stream handler supports a small set commands for listing and controlling daemon functions:
http://localhost:8983/collection/stream?action=list
This command will provide a listing of the current daemon's running on the specific node along with there current
state.
http://localhost:8983/collection/stream?action=stop&id=daemonId
This command will stop a specific daemon function but leave it resident in memory
http://localhost:8983/collection/stream?action=start&id=daemonId
This command will start a specific daemon function that has been stopped.
http://localhost:8983/collection/stream?action=kill&id=daemonId
This command will stop a specific daemon function and remove it from memory.
Continous Pull Streaming
The DaemonStream java class (part of the Solrj libraries) can also be embedded in a java application to provide
continuous pull streaming. Sample code:
StreamContext context = new StreamContext()
SolrClientCache cache = new SolrClientCache();
context.setSolrClientCache(cache);
Map topicQueryParams = new HashMap();
topicQueryParams.put("q","hello"); // The query for the topic
topicQueryparams.put("rows", "500"); // How many rows to fetch during each run
topicQueryparams.put("fl", "id, "title"); // The field list to return with the
documents
TopicStream topicStream = new TopicStream(zkHost, // Host address for the
zookeeper service housing the collections
"checkpoints", // The collection to store
the topic checkpoints
"topicData", // The collection to query
for the topic records
"topicId", // The id of the topic
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