04 Real-time aggregates · Instructor

Timing

20 minutes.

Talk track

• The MV processes inserted blocks; it does not rescan history on every dashboard refresh.
• State functions store partial aggregate states; matching Merge functions finalize them.
• OHLC is quote midpoint only. Mixing order-level change prices and last trades would make the chart meaningless.
• The collector deduplicates before the MV sees rows; ReplacingMergeTree after the fact would not undo aggregate double-counting.

Common failures

• Aggregate empty: verify raw midpoint rows exist and the MV was created before ingestion.
• MV created late: restart fixture mode after creating it, or accept only new rows.
• Old newest minute: check collector health before debugging SQL.

Reset

For a fresh aggregate without deleting raw data, recreate the target and MV, then allow new events to populate it. Do not run OPTIMIZE TABLE FINAL.