couchbase

Couchbase

Couchbase works as a Key-Value store (managed memory cache) + Document Database. It is famous for its "memory-first" architecture and N1QL (SQL for JSON).

When to Use

• Memory-First NoSQL Document Store: Applications requiring sub-millisecond document lookups powered by an integrated managed memory cache.
• SQL for JSON (N1QL / SQL++): Querying JSON documents using familiar SQL syntax with joins, nested arrays, and subqueries.
• Distributed Key-Value + Full-Text Search: Unifying key-value caching, document storage, and vector/full-text search in a single cluster.
• Mobile Edge Data Sync (Couchbase Lite): Synchronizing embedded mobile database instances with cloud clusters using Sync Gateway.

Quick Start

-- N1QL Query
SELECT u.name, ARRAY_AGG(o.item) as orders
FROM `travel-sample`.inventory.users u
JOIN `travel-sample`.inventory.orders o ON u.id = o.user_id
WHERE u.city = "Paris"
GROUP BY u.name;

Core Concepts

Memory-First VBucket Architecture

Documents are mapped across 1024 virtual buckets (vBuckets), cached directly in RAM before being asynchronously written to disk:

[ Application Client ] ──Sub-Millisecond Read/Write──→ [ Managed Memory Cache (RAM) ]
                                                                 │ (Async Flush)
                                                                 ▼
                                                        [ Append-Only Disk Storage ]

SQL++ (N1QL) Declarative JSON Queries

Executes full SQL expressions over schemaless JSON structures:

-- Query nested JSON orders in Couchbase SQL++
SELECT
  meta().id AS orderId,
  customer.email,
  ARRAY_SUM(items[*].price) AS totalAmount
FROM `commerce`.`orders` AS o
WHERE status = 'PAID'
  AND ANY item IN items SATISFIES item.category = 'Electronics' END
ORDER BY totalAmount DESC
LIMIT 20;

Scopes and Collections Multi-Tenancy

Organizes documents into logical namespaces mimicking relational databases: