Couchbase Developer flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Document key design

Keys must be unique per bucket and should spread writes across vBuckets; include a high-cardinality component such as a user ID or counter to avoid hot spots.

Embed vs reference

Embed bounded child data read with the parent; reference large, shared, or independently updated data. Couchbase has no joins, so N1QL JOIN is the only cross-document option.

USE KEYS clause

N1QL SELECT ... USE KEYS ['doc::1'] fetches documents directly by key without an index scan, making point reads fast and predictable.

Covering index

An index that includes all fields a query needs (via INCLUDE) so the query engine answers from the index without fetching the document, reducing latency and I/O.

request_plus consistency

A scan consistency mode where the query waits until indexes have caught up with the request time, guaranteeing read-after-write at the cost of added latency.

UNNEST in N1QL

UNNEST flattens an array field into rows so each element can be filtered or joined; use it to query inside arrays without application-side processing.

MERGE statement

N1QL MERGE INTO target USING source ON condition performs conditional insert, update, or delete in one statement, useful for upsert-style logic.

EXPLAIN plan

EXPLAIN returns the query plan; a primary scan over the whole bucket indicates a missing or unused secondary index and should be fixed before production.

Scope and collection

Couchbase 7.0+ logical containers inside a bucket; collections group documents and indexes, while scopes group collections, enabling multi-tenant isolation without separate buckets.

Cluster.connect

SDK 3.x entry point: Cluster.connect('couchbase://host', options) returns a Cluster; then call bucket(), scope(), and collection() to reach data.

CAS optimistic concurrency

Each document has a CAS value; pass the CAS from a read into replace or mutateIn. A mismatch throws CasMismatchException, signaling a concurrent modification.

Durability levels

MutateInOptions durability (MAJORITY, PERSIST_TO_MAJORITY) or PersistTo/ReplicateTo control how many replicas must acknowledge a write before it returns.

Sub-document operations

lookupIn and mutateIn read or modify specific paths inside a document without transferring the whole body, reducing bandwidth and latency for large documents.

Error classification

SDK errors fall into transient (retry with backoff), ambiguous (outcome unknown, re-read), and permanent (do not retry); correct classification prevents duplicate writes.

SDK transactions

Couchbase 7.0+ transactions run via cluster.transactions().run(lambda); operations inside commit atomically across collections and roll back on failure.

GetResult contentAs

GetResult.contentAs(Class) deserializes the document body; check exists() first because a missing document returns an empty result rather than throwing.

Reactive and async APIs

Java, .NET, and Node.js SDKs offer reactive or async variants; blocking calls on event-loop threads cause stalls, so use async methods in those runtimes.

Connection string schemes

couchbase:// uses plain TCP; couchbases:// enables TLS. The string lists seed nodes and optional options such as timeouts and compression.

vBuckets

Each bucket is divided into 1024 vBuckets distributed across data nodes; rebalance moves vBuckets to equalize load and replicas protect them during node loss.

Graceful vs hard failover

Graceful failover waits for data to be replicated before removing a node; hard failover removes it immediately and may lose unreplicated writes.

Auto-failover

A cluster setting that triggers failover after a node is unresponsive for a configured timeout; it requires at least one replica to preserve availability.

Bucket RAM quota

The memory allocated to a bucket's cache; too small a quota causes frequent disk fetches, while too large a quota starves other services on the node.

cbbackupmgr

The backup and restore tool for Couchbase; it supports full and incremental backups, merges, and restore to a cluster, and should be tested regularly.

RBAC roles

Role-based access control assigns privileges such as data reader, data writer, or query to users; applications should use least-privilege accounts, not Administrator.

Rolling upgrade

Upgrade one node at a time, rebalancing after each, so the cluster stays online; verify SDK and index compatibility before starting.

Service placement

Data, index, query, search, analytics, and eventing services can run on selected nodes; placement affects failover capacity and query performance.

Couchbase Lite

An embedded NoSQL database on mobile and edge devices; it stores documents locally and replicates with Sync Gateway or Couchbase Server.

Sync Gateway

The server component that authenticates mobile clients and replicates documents between Couchbase Lite and Couchbase Server using the replication protocol.

Push vs pull replication

Push sends local changes to the server; pull fetches remote changes to the device. Continuous replication keeps both running, one-shot runs once.

Conflict resolution

When the same document changes on device and server, Couchbase Lite resolves conflicts with a default last-write-wins rule or a custom conflict handler.

Channels and roles

Sync Gateway assigns documents to channels via the sync function; users with access to a channel receive those documents during replication.

Delta sync

A replication optimization that sends only changed document fields instead of full bodies, reducing bandwidth for mobile and edge connections.