1. Scalability and Performance: Clickhouse is designed for high performance analytical processing and can handle massive amounts of data with low latency. It is horizontally scalable and can process billions of rows per second. On the other hand, Couchbase is a distributed NoSQL database that provides high scalability and performance for both read and write operations. It can handle large workloads and scale out horizontally by adding more nodes.

2. Data Model: Clickhouse is a columnar database that stores data in columns rather than rows, which allows for efficient compression and faster query execution. It is optimized for analytical queries and aggregations. In contrast, Couchbase is a document-oriented database that stores data in JSON-like documents. It offers flexible schema-less data model, which allows for easy data modeling and makes it suitable for a wide range of use cases.

3. Consistency Model: Clickhouse is an eventual consistency database, which means that it may not provide real-time consistency across all replicas in a distributed setup. It prioritizes availability and partition tolerance over strict consistency. On the other hand, Couchbase provides strong consistency by default, ensuring that every read receives the most recent write. It uses a distributed consensus protocol to ensure consistency across replicas.

4. Query Language: Clickhouse uses its own SQL-like query language called ClickHouse SQL (CHQL) for querying and manipulating data. It supports advanced analytical features such as window functions, materialized views, and sampling. Couchbase uses N1QL (pronounced as "nickel") as its query language, which is a SQL-like query language for JSON documents. It extends SQL to provide querying flexibility over complex JSON structures.

5. Data Replication: Clickhouse supports asynchronous data replication, where data is replicated to replicas in the background. It provides configurable replication settings for controlling data consistency and performance. Couchbase also supports data replication but offers both synchronous and asynchronous replication options. It provides replication across multiple data centers for high availability and disaster recovery.

6. Caching: Clickhouse provides efficient caching mechanisms to improve query performance, including a block cache, page cache, and a query cache. It leverages the available RAM to cache frequently accessed data and results. Couchbase also provides a built-in caching mechanism that can be configured to cache frequently accessed data in memory. It uses an intelligent caching strategy to optimize data access and reduce latency.

In Summary, Clickhouse is a high-performance columnar database with eventual consistency, while Couchbase is a distributed NoSQL database based on a document-oriented model with strong consistency.