2nd/10_Wiki/Topics/AI_and_ML/카산드라(Cassandra).md

---
id: wiki-2026-0508-카산드라-cassandra
title: 카산드라(Cassandra)
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [Apache Cassandra, Cassandra, C*]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [database, nosql, distributed, wide-column, ap-system]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: Java/CQL
  framework: Apache Cassandra 5.0
---

# 카산드라 (Cassandra)

## 매 한 줄
> **"매 write-optimized · 매 masterless · 매 AP 의 매 wide-column store"**. 매 Apache Cassandra 5.0 (2026) 은 매 Dynamo-style replication + 매 BigTable-style data model 의 매 합 — 매 single-region 1M+ writes/sec 의 매 linear scale, 매 multi-DC active-active, 매 tunable consistency. 매 partition key 설계 가 매 흥망 — 매 잘못된 model 은 매 hotspot · 매 large partition 의 매 재앙.

## 매 핵심

### 매 architecture
- **매 Masterless**: 매 모든 node 가 매 동등 — 매 single point of failure 부재.
- **매 Consistent hashing**: 매 token ring + 매 vnode (default 16) — 매 even distribution.
- **매 Replication**: 매 RF=3 의 매 typical, 매 NetworkTopologyStrategy 로 매 multi-DC.
- **매 Gossip**: 매 peer-to-peer cluster state.
- **매 LSM tree storage**: 매 memtable → SSTable, 매 compaction (STCS / LCS / TWCS).

### 매 consistency
- **매 Tunable**: ANY, ONE, QUORUM, LOCAL_QUORUM, EACH_QUORUM, ALL.
- **매 Strong**: R+W > N (e.g., RF=3, R=QUORUM, W=QUORUM).
- **매 Eventual**: ONE/ANY — 매 fast 하지만 매 stale read 가능.
- **매 LWT (Paxos)**: 매 conditional write — 매 비싸지만 매 linearizable.

### 매 응용
1. 매 time-series (IoT, metrics, logs).
2. 매 messaging / 매 feed (Discord 의 매 trillion+ msgs).
3. 매 session / 매 cart store.
4. 매 GenAI 의 매 vector + Cassandra 5 의 매 SAI vector index.

## 💻 패턴

### Pattern 1: 매 Schema Design (query-first)
```sql
-- 매 BAD: 매 hotspot — 매 single partition
CREATE TABLE messages (
  channel_id uuid PRIMARY KEY,
  msg_id timeuuid,
  body text
);

-- 매 GOOD: 매 bucketed time partition
CREATE TABLE messages (
  channel_id uuid,
  bucket text,        -- 매 'YYYY-MM-DD'
  msg_id timeuuid,
  body text,
  PRIMARY KEY ((channel_id, bucket), msg_id)
) WITH CLUSTERING ORDER BY (msg_id DESC);
```

### Pattern 2: 매 Vector Search (Cassandra 5 SAI)
```sql
CREATE TABLE products (
  id uuid PRIMARY KEY,
  name text,
  embedding vector<float, 1536>
);

CREATE CUSTOM INDEX ON products(embedding)
  USING 'StorageAttachedIndex'
  WITH OPTIONS = { 'similarity_function' : 'cosine' };

-- 매 ANN search
SELECT id, name FROM products
ORDER BY embedding ANN OF [0.1, 0.2, ...]
LIMIT 10;
```

### Pattern 3: 매 Driver Async (Java)
```java
CqlSession session = CqlSession.builder().build();
PreparedStatement ps = session.prepare(
  "INSERT INTO messages (channel_id, bucket, msg_id, body) VALUES (?, ?, ?, ?)"
);

CompletionStage<AsyncResultSet> f = session.executeAsync(
  ps.bind(channelId, bucket, msgId, body)
    .setConsistencyLevel(ConsistencyLevel.LOCAL_QUORUM)
);
```

### Pattern 4: 매 Compaction Strategy 선택
```sql
-- 매 time-series → TWCS
ALTER TABLE metrics WITH compaction = {
  'class': 'TimeWindowCompactionStrategy',
  'compaction_window_size': '1',
  'compaction_window_unit': 'DAYS'
};

-- 매 read-heavy → LCS
ALTER TABLE users WITH compaction = {
  'class': 'LeveledCompactionStrategy',
  'sstable_size_in_mb': '160'
};

-- 매 write-heavy general → STCS (default)
```

### Pattern 5: 매 Multi-DC Replication
```sql
CREATE KEYSPACE app
  WITH replication = {
    'class': 'NetworkTopologyStrategy',
    'us-east': 3,
    'eu-west': 3,
    'ap-northeast': 2
  } AND durable_writes = true;
```

### Pattern 6: 매 LWT (conditional)
```sql
-- 매 unique constraint
INSERT INTO users (email, id) VALUES ('a@b.com', uuid())
  IF NOT EXISTS;

-- 매 비쌈 — 매 4 round trip Paxos. 매 hot path 회피.
```

### Pattern 7: 매 Anti-pattern 진단
```sql
-- 매 nodetool tablestats 로 매 large partition 확인
-- nodetool tablestats keyspace.table | grep "Compacted partition maximum"

-- 매 100MB+ partition = 매 redesign signal
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| 매 write 1M+/sec | Cassandra (자연 fit) |
| 매 strong consistency 필수 | LWT or 매 다른 DB (CockroachDB, Spanner) |
| 매 ad-hoc query / JOIN | Postgres / Trino — 매 Cassandra 부적합 |
| 매 time-series | Cassandra + TWCS or ScyllaDB |
| 매 vector + scale | Cassandra 5 SAI or Milvus/Qdrant |
| 매 small data (< 1TB) | Postgres — 매 Cassandra overkill |

**기본값**: 매 query-first schema, 매 LOCAL_QUORUM, 매 RF=3, 매 partition < 100MB.

## 🔗 Graph
- 부모: [[NoSQL]] · [[Distributed Database]]
- 변형: [[ScyllaDB]] · [[DynamoDB]]
- 응용: [[Time Series Database]] · [[Messaging Platform]]
- Adjacent: [[Vector Database]] · [[CAP Theorem]]

## 🤖 LLM 활용
**언제**: 매 large-scale write workload 의 매 design, 매 multi-DC active-active 요건, 매 time-series storage, 매 schema review.
**언제 X**: 매 transactional / OLTP / JOIN 매 heavy — 매 RDBMS 가 매 적합. 매 small data — 매 over-engineering.

## ❌ 안티패턴
- **매 Large partition (>100MB)**: 매 OOM, 매 compaction failure, 매 read latency 폭발.
- **매 Hotspot key**: 매 single-channel 모든 msg → 매 partition 폭발.
- **매 ALLOW FILTERING**: 매 full scan — 매 production X.
- **매 Secondary index 의 매 high cardinality**: 매 매번 매 fanout — 매 SAI 사용.
- **매 LWT 의 매 hot path**: 매 4× latency.
- **매 SQL mindset (JOIN, GROUP BY)**: 매 denormalize 의 매 의무.

## 🧪 검증 / 중복
- Verified (Apache Cassandra 5.0 docs, DataStax docs, Discord engineering blog 2026).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — Cassandra 5.0 (SAI vector) full 정리 |