ClickHouse is awesome, but there's a newer OLAP database in town: Apache Pinot, and it is significantly better:
https://pinot.apache.org/Here's why it is better:
1. User-facing analytics vs. business analytics. Pinot was designed for user-facing analytics (meaning analytics result is used by end-user (for example, "what is the expected delivery time for this restaurant?"). The demands are much higher, including latency, freshness, concurrency and uptime.
2. Better architecture. To scale out ClickHouse uses sharding. Which means if you want to add a node you have to bring down the database, re-partition the database and reload the data, then bring it back up. Expect downtime of 1 or 2 days at least. Pinot on the other hand uses segments, which is smaller (but self-contained) pieces of data, and there are lots of segments on each node. When you add a node, Pinot just moves around segments, no downtime needed. Furthermore, for high availability ClickHouse uses replicas. Each shard needs 1 or 2 replicas for HA. Pinot does not have shards vs replica nodes. Instead each segment is replicated to 2 to 3 nodes. This is better for hardware utilization.
3. Pre-aggregation. OLAP cubes became popular in the 1990s. They pre-aggregate data to make queries significantly faster, but the downside is high storage cost. ClickHouse doesn't have the equivalent of OLAP cubes at all. Pinot has something better than OLAP cubes: Star trees. Like cubes, star trees pre-aggregate data along multiple dimensions, but don't need as much storage.
Here's why it is better:
1. User-facing analytics vs. business analytics. Pinot was designed for user-facing analytics (meaning analytics result is used by end-user (for example, "what is the expected delivery time for this restaurant?"). The demands are much higher, including latency, freshness, concurrency and uptime.
2. Better architecture. To scale out ClickHouse uses sharding. Which means if you want to add a node you have to bring down the database, re-partition the database and reload the data, then bring it back up. Expect downtime of 1 or 2 days at least. Pinot on the other hand uses segments, which is smaller (but self-contained) pieces of data, and there are lots of segments on each node. When you add a node, Pinot just moves around segments, no downtime needed. Furthermore, for high availability ClickHouse uses replicas. Each shard needs 1 or 2 replicas for HA. Pinot does not have shards vs replica nodes. Instead each segment is replicated to 2 to 3 nodes. This is better for hardware utilization.
3. Pre-aggregation. OLAP cubes became popular in the 1990s. They pre-aggregate data to make queries significantly faster, but the downside is high storage cost. ClickHouse doesn't have the equivalent of OLAP cubes at all. Pinot has something better than OLAP cubes: Star trees. Like cubes, star trees pre-aggregate data along multiple dimensions, but don't need as much storage.