Shuffling shards to balance the load
Several shard shuffle strategies are available to balance the load and minimize data that is transferred from non-local nodes.
DataStax Enterprise uses a shuffling technique to balance the load, and also attempts to minimize the number of shards that are queried as well as the amount of data that is transferred from non-local nodes.
To balance the load in a distributed environment, choose from several strategies for shuffling the shards. The shard shuffling strategy specifies how one DSE Search node is selected over others for reading the Solr data. The value of the shard.shuffling.strategy parameter must be one of the following values:
- host
Shards are selected based on the host that received the query.
- query
Shards are selected based on the query string.
- host_query
Shards are selected by host x query.
- random
Different random set of shards are selected with each request (default).
- SEED
Selects the same shard from one query to another.
Methods for selecting shard shuffling strategy
- Append
shard.shuffling.strategy = <strategy>
to the HTTP API query. For example:http://localhost:8983/solr/wiki.solr/select?q=title:natio*&shard.shuffling.strategy=host
Issuing this query determines the shard shuffling strategy for this query only.
- Create a dse-search.properties file and POST it to Solr.
For example:
- Create the dse-search.properties file with the following
contents:
shard.shuffling.strategy=query
- Post the command to DSE Search. For
example:
curl -v --data-binary @dse-search.properties http://localhost:8983/solr/resource/wiki.solr/dse-search.properties
Posting the command determines the shard shuffling strategy for all queries to the given Solr core. The strategy is propagated to all nodes and saved in Solr core metadata.
- Create the dse-search.properties file with the following
contents:
-
Set the following parameters to use the SEED strategy:
- Pass the
shard.shuffling.strategy=SEED
as a request parameter. - Specify a request parameter, such as an IP address or any string, using the
shard.shuffling.seed
parameter. When you reuse the same seed value between queries on a stable cluster, the same shard strategy will be in effect.Every time you pass the same string, the same list of shards is queried, regardless of the target node you actually query; if you change the string, a different list of shards are queried.
- Verify that the strategy was maintained by passing the
shards.info=true request
parameter. For example:curl "http://localhost:8983/solr/demo.solr/select/?q=text:search&shards.info=true&shard.shuffling.strategy=SEED&shard.shuffling.seed=192.168.0.1&rows=0"
- Pass the
Shuffling does not always result in the node selection that you might expect. For example, using a replication factor of 3 with six nodes, the best and only solution is a two-shard solution where half of the data is read from the originator node and half from another node. A three-shard solution would be inefficient.