Web / Apache Solr Interview questions
How does Solr replication work in standalone (master-slave) mode?
In classic standalone replication, one core is designated the master and one or more cores act as slaves. The master handles all writes; slaves handle read traffic and periodically pull data from the master.
- A slave's ReplicationHandler polls the master on a configured interval, checking the master's index version.
- If the master's version is newer, the slave downloads the changed Lucene segment files over HTTP.
- Once the download finishes, the slave opens a new searcher on the updated index and swaps it in.
This is pull-based replication, not push-based, and it's inherently eventually consistent - slaves lag behind the master by roughly the poll interval. Because failover is manual and there's no automatic sharding, this mode is mostly seen today in legacy deployments or very small single-shard use cases rather than new production systems.
Is standalone Solr replication push-based or pull-based?
What does a slave download from the master when it detects a newer index version?
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