Optimizing Queries in InfluxDB 3.0 Using Progressive Evaluation

InfluxDB 3.0 introduces optimized SQL queries using progressive evaluation, which significantly improves "most recent values" query performance. This technique is currently only available for SQL queries with the clause ORDER BY time DESC or ASC and has certain limitations such as expressions, aliases, and aggregations on the SELECT clause. Progressive evaluation can be identified in the query plan by the presence of ProgressiveEvalExec. The data organization in InfluxDB 3.0 consists of four stages: C (not yet persisted), L0 (newly ingested and persisted), L1 (compacted files), and L2 (beyond the scope of this topic). Progressive evaluation benefits queries by fetching data from non-overlapped files progressively, reducing CPU time and potentially improving latency for other queries on the system.