InfluxDB is a time-series database that can be used to store and query large amounts of data, particularly those with temporal relationships. The database has various features such as Continuous Queries (CQs) which allow for real-time calculations on the data stored in it. Shard group duration recommendations are crucial for efficient data storage and retrieval, and InfluxDB provides guidelines for configuring shard group durations based on retention policies and query time ranges. Users can configure shard groups to have at least 100,000 points per shard group and 1,000 points per series to optimize performance. Additionally, users can use the HTTP API to query data from non-DEFAULT retention policies by fully qualifying measurements in the query's FROM clause with their database and retention policy names.