brainy/docs/architecture/index-architecture.md

Index Architecture

Brainy uses a sophisticated 4-index architecture that enables "Triple Intelligence" - the unified combination of vector similarity, graph relationships, and metadata filtering. This document provides a comprehensive architectural overview of how these indexes work internally and coordinate with each other.

Overview: The Four Core Indexes

Index	Purpose	Data Structure	Complexity	File Location
MetadataIndex	Fast metadata filtering	Inverted indexes + sorted arrays	O(1) exact, O(log n) ranges	src/utils/metadataIndex.ts
HNSWIndex	Vector similarity search	Hierarchical graphs	O(log n) search	src/hnsw/hnswIndex.ts
GraphAdjacencyIndex	Relationship traversal	Bidirectional adjacency maps	O(1) per hop	src/graph/graphAdjacencyIndex.ts
DeletedItemsIndex	Soft-delete tracking	Simple Set	O(1) all ops	src/utils/deletedItemsIndex.ts

All four indexes share a UnifiedCache for coordinated memory management, ensuring fair resource allocation and preventing any single index from monopolizing memory.

1. MetadataIndex - Fast Field Filtering

Purpose: Enable O(1) field-value lookups and O(log n) range queries on metadata fields.

Internal Architecture

class MetadataIndexManager {
  // Inverted indexes: field:value → Set<entityId>
  private indexCache = new Map<string, MetadataIndexEntry>()

  // Sorted indices for range queries
  private sortedIndices = new Map<string, SortedFieldIndex>()

  // Field statistics for query optimization
  private fieldStats = new Map<string, FieldStats>()

  // Type-field affinity for NLP understanding
  private typeFieldAffinity = new Map<string, Map<string, number>>()

  // Shared memory management
  private unifiedCache: UnifiedCache
}

Key Data Structures

Inverted Index

// Example: field="status", value="active"
// Key: "status:active"
// Value: MetadataIndexEntry {
//   ids: Set(['id1', 'id2', 'id3']),  // All entities with status="active"
//   metadata: { lastUpdated: timestamp, count: 3 }
// }

Performance: O(1) lookup for exact matches

Sorted Index

// Example: field="publishDate" (numeric/temporal)
// Key: "publishDate"
// Value: SortedFieldIndex {
//   entries: [
//     [1609459200000, Set(['id1', 'id2'])],  // Jan 1, 2021
//     [1640995200000, Set(['id3', 'id4'])],  // Jan 1, 2022
//     [1672531200000, Set(['id5', 'id6'])]   // Jan 1, 2023
//   ]
// }

Performance: O(log n) binary search + O(k) result collection

Type-Field Affinity

// Tracks which fields are commonly used with which types
// Example:
// typeFieldAffinity.get('character') → {
//   'name': 127,      // 127 characters have a 'name' field
//   'age': 89,        // 89 characters have an 'age' field
//   'alignment': 45   // 45 characters have an 'alignment' field
// }

Use case: Enables NLP to understand "find characters named John" → knows 'name' is a character field

Temporal Bucketing (v3.41.0)

Problem Solved: High-cardinality timestamp fields created massive file pollution.

• Example: 575 entities with unique timestamps → 358,407 index files (98.7% pollution!)

Solution: Automatic bucketing of temporal fields to 1-minute intervals.

// In normalizeValue(value, field):
if (field && typeof value === 'number') {
  const fieldLower = field.toLowerCase()
  const isTemporal = fieldLower.includes('time') ||
                     fieldLower.includes('date') ||
                     fieldLower.includes('accessed') ||
                     fieldLower.includes('modified') ||
                     fieldLower.includes('created') ||
                     fieldLower.includes('updated')

  if (isTemporal) {
    // Bucket to 1-minute intervals
    const bucketSize = 60000 // milliseconds
    const bucketed = Math.floor(value / bucketSize) * bucketSize
    return bucketed.toString()
  }
}

Benefits:

• ✅ Reduces 575 unique timestamps → ~10 buckets
• ✅ File count: 358,407 → ~4,600 (98.7% reduction)
• ✅ Zero configuration - automatic field name detection
• ✅ Still enables range queries (not excluded like before)
• ✅ 1-minute precision sufficient for most use cases

Field Name Detection: Automatically buckets fields with these keywords:

• time, date, accessed, modified, created, updated
• Examples: timestamp, createdAt, lastModified, birthdate, eventTime

Operations

// Add to index (src/brainy.ts:387)
await this.metadataIndex.addToIndex(id, metadata)

// Query exact match
const ids = await this.metadataIndex.getIds('status', 'active')

// Query range
const ids = await this.metadataIndex.getIdsForFilter({
  publishDate: { greaterThan: 1640995200000 }
})

// Filter discovery (what values exist for a field)
const values = await this.metadataIndex.getFilterValues('status')
// → ['active', 'archived', 'draft']

// Statistics (O(1))
const totalEntities = this.metadataIndex.getTotalEntityCount()
const typeBreakdown = this.metadataIndex.getAllEntityCounts()
// → Map { 'character': 127, 'item': 89, 'location': 45 }

Excluded Fields

Some fields are excluded from indexing to prevent pollution:

const DEFAULT_EXCLUDE_FIELDS = [
  'id',               // Primary key (redundant to index)
  'uuid',             // Alternative primary key
  'vector',           // High-dimensional data
  'embedding',        // Same as vector
  'content',          // Large text content
  'description',      // Large text content
  'metadata',         // Nested object (too large)
  'data'              // Generic nested object
]

Note: Timestamp fields like modified, accessed, created are NO LONGER excluded as of v3.41.0 - they are indexed with automatic bucketing.

2. HNSWIndex - Vector Similarity Search

Purpose: O(log n) semantic similarity search using vector embeddings.

Internal Architecture

class HNSWIndex {
  // Per-noun indexes for efficiency
  private nouns: Map<string, HNSWNoun> = new Map()

  // Global entry point for search
  private entryPointId: string | null = null
  private maxLevel = 0

  // Shared memory management
  private unifiedCache: UnifiedCache
  private storage: BaseStorage | null = null
}

// Each noun has its own HNSW graph
class HNSWNoun {
  noun: string
  nodes: Map<string, HNSWNode>
  entryPointId: string | null
  maxLevel: number
}

// Each node in the graph
class HNSWNode {
  id: string
  vector: Vector | null  // Lazy-loaded from storage
  level: number
  connections: Map<number, string[]>  // level → neighbor IDs
}

Hierarchical Graph Structure

HNSW builds a multi-layered graph:

Layer 2: [entry] ←→ [node1]                    (sparse, long-range connections)
           ↓         ↓
Layer 1: [entry] ←→ [node1] ←→ [node2] ←→ [node3]  (medium density)
           ↓         ↓         ↓         ↓
Layer 0: [entry] ←→ [node1] ←→ [node2] ←→ [node3] ←→ [node4] ←→ [node5]  (dense, all nodes)

Search Algorithm:

1. Start at entry point in top layer
2. Greedy search for nearest neighbor in current layer
3. Move down to next layer with found neighbor
4. Repeat until reaching layer 0
5. Return k nearest neighbors

Complexity: O(log n) due to hierarchical structure

Adaptive Vector Loading

Vectors are lazy-loaded on demand based on memory availability:

private async getVectorSafe(noun: HNSWNoun): Promise<Vector> {
  // Check UnifiedCache first
  const cached = this.unifiedCache.get(noun.id)
  if (cached) return cached

  // Load from storage if memory available
  if (this.unifiedCache.canCache()) {
    const vector = await this.storage.loadVector(noun.id)
    this.unifiedCache.set(noun.id, vector)
    return vector
  }

  // Load transiently if memory pressure
  return await this.storage.loadVector(noun.id)
}

Operations

// Add entity (src/brainy.ts:add)
await this.index.addEntity(id, vector, noun)

// Search for similar vectors
const results = await this.index.search(queryVector, k, threshold)
// Returns: Array<{id: string, similarity: number}>

// Rebuild from storage
await this.index.rebuild()

3. GraphAdjacencyIndex - O(1) Relationship Traversal

Purpose: Constant-time neighbor lookups regardless of graph size.

Internal Architecture

class GraphAdjacencyIndex {
  // O(1) bidirectional lookups
  private sourceIndex = new Map<string, Set<string>>()  // sourceId → targetIds
  private targetIndex = new Map<string, Set<string>>()  // targetId → sourceIds

  // Full relationship data
  private verbIndex = new Map<string, GraphVerb>()      // verbId → metadata

  // Statistics
  private relationshipCountsByType = new Map<string, number>()

  // Shared memory
  private unifiedCache: UnifiedCache
  private storage: BaseStorage
}

Key Innovation: Bidirectional Adjacency

Core Insight: Store BOTH directions of each relationship for O(1) lookups.

// Example: Alice KNOWS Bob
// verbId = "verb-123"

// Source index: Alice → Bob
sourceIndex.set('alice', Set(['bob']))

// Target index: Bob ← Alice
targetIndex.set('bob', Set(['alice']))

// Full metadata
verbIndex.set('verb-123', {
  id: 'verb-123',
  verb: 'knows',
  source: 'alice',
  target: 'bob',
  metadata: { since: 2020 }
})

Result: Finding Alice's friends OR Bob's friends is O(1) - just one Map lookup!

Operations

// Add relationship (src/brainy.ts:relate)
await this.graphIndex.addRelationship(verbId, sourceId, targetId, verb)

// Get neighbors (O(1) per hop)
const outgoing = await this.graphIndex.getNeighbors(id, 'out')  // Who does id point to?
const incoming = await this.graphIndex.getNeighbors(id, 'in')   // Who points to id?
const both = await this.graphIndex.getNeighbors(id, 'both')     // All neighbors

// Get relationships
const verbs = await this.graphIndex.getRelationships(sourceId, targetId)

// Statistics (O(1))
const totalRelationships = this.graphIndex.getTotalRelationshipCount()
const byType = this.graphIndex.getRelationshipCountsByType()
// → Map { 'knows': 45, 'created': 23, 'located_at': 12 }

Graph Traversal

The index supports multi-hop traversal:

// Find all entities within 2 hops
const reachable = await this.graphIndex.traverse({
  startId: 'alice',
  depth: 2,
  direction: 'out'
})
// Complexity: O(V + E) breadth-first search, but each neighbor lookup is O(1)

4. DeletedItemsIndex - Soft-Delete Tracking

Purpose: O(1) tracking of soft-deleted items without removing data.

Internal Architecture

class DeletedItemsIndex {
  private deletedIds: Set<string> = new Set()
  private deletedCount: number = 0
  private storage: BaseStorage
}

Simplicity is key: Just a Set of deleted IDs. No complex logic needed.

Operations

// Mark as deleted
this.deletedItemsIndex.markDeleted(id)  // O(1)

// Check if deleted
const isDeleted = this.deletedItemsIndex.isDeleted(id)  // O(1)

// Filter out deleted items
const active = this.deletedItemsIndex.filterDeleted(results)  // O(n)

// Restore
this.deletedItemsIndex.markRestored(id)  // O(1)

// Get all deleted
const deleted = this.deletedItemsIndex.getAllDeleted()  // O(1) - returns Set

Integration

All query results are filtered through the deleted items index:

// In brainy.find() (src/brainy.ts:1026+)
let results = await this.performSearch(query)

// Filter out deleted items before returning
results = results.filter(r => !this.deletedItemsIndex.isDeleted(r.id))

Shared Memory Management: UnifiedCache

All four indexes share a single UnifiedCache instance for coordinated memory management.

Architecture

class UnifiedCache {
  private cache: Map<string, CachedItem> = new Map()
  private maxSize: number
  private currentSize: number = 0
  private evictionPolicy: 'LRU' | 'LFU' = 'LRU'
}

// Each index gets the same cache instance
const unifiedCache = new UnifiedCache({ maxSize: 1000 })
this.metadataIndex = new MetadataIndexManager(storage, { unifiedCache })
this.hnswIndex = new HNSWIndex(storage, { unifiedCache })
this.graphIndex = new GraphAdjacencyIndex(storage, { unifiedCache })

Benefits

1. Fair Resource Allocation: All indexes compete for the same memory pool
2. Prevents Monopolization: No single index can starve others of memory
3. Coordinated Eviction: LRU eviction across all cached items system-wide
4. Memory Pressure Handling: Automatic cache shrinking when memory is tight
5. Adaptive Loading: Indexes load data transiently under memory pressure

Cache Key Patterns

Each index uses different key prefixes:

// Metadata index
cache.set(`meta:${field}:${value}`, indexEntry)

// HNSW index
cache.set(`vector:${id}`, vectorData)

// Graph index
cache.set(`graph:${sourceId}`, neighbors)

// Deleted items (no caching needed - uses Set)

How Indexes Work Together

1. Entity Creation (brainy.add())

// src/brainy.ts:add()
async add(params: AddParams): Promise<string> {
  const id = generateId()
  const vector = await this.embedder(params.content)

  // Add to metadata index (field filtering)
  await this.metadataIndex.addToIndex(id, params.metadata)

  // Add to HNSW index (vector search)
  await this.index.addEntity(id, vector, params.noun)

  // Relationships added via separate relate() calls

  return id
}

2. Entity Search (brainy.find())

// src/brainy.ts:find()
async find(query: FindQuery): Promise<Result[]> {
  let results: Result[] = []

  // Step 1: Metadata filtering (fast pre-filter)
  if (query.where) {
    const filteredIds = await this.metadataIndex.getIdsForFilter(query.where)
    results = await this.getEntitiesByIds(filteredIds)
  }

  // Step 2: Vector similarity search (semantic ranking)
  if (query.like) {
    const queryVector = await this.embedder(query.like)
    const vectorResults = await this.index.search(queryVector, query.limit)

    // Intersect or union with metadata results
    results = this.combineResults(results, vectorResults)
  }

  // Step 3: Graph traversal (relationship filtering)
  if (query.connected) {
    const connectedIds = await this.graphIndex.traverse(query.connected)
    results = results.filter(r => connectedIds.includes(r.id))
  }

  // Step 4: Filter deleted items
  results = results.filter(r => !this.deletedItemsIndex.isDeleted(r.id))

  return results
}

3. Entity Update (brainy.update())

// src/brainy.ts:update()
async update(params: UpdateParams): Promise<void> {
  const existing = await this.get(params.id)

  // Update metadata index (remove old, add new)
  await this.metadataIndex.removeFromIndex(params.id, existing.metadata)
  await this.metadataIndex.addToIndex(params.id, params.metadata)

  // Update HNSW index (re-embed if content changed)
  if (params.content) {
    const newVector = await this.embedder(params.content)
    await this.index.updateEntity(params.id, newVector)
  }

  // Graph relationships unchanged (managed separately)
}

4. Statistics (brainy.stats())

All indexes provide O(1) statistics:

// src/brainy.ts:stats()
async stats(): Promise<Statistics> {
  return {
    // From metadata index
    entities: this.metadataIndex.getTotalEntityCount(),
    entityTypes: this.metadataIndex.getAllEntityCounts(),

    // From graph index
    relationships: this.graphIndex.getTotalRelationshipCount(),
    relationshipTypes: this.graphIndex.getRelationshipCountsByType(),

    // From deleted items index
    deletedItems: this.deletedItemsIndex.getDeletedCount(),

    // From HNSW index
    vectorIndexSize: this.index.getSize()
  }
}

5. Index Rebuilding

All indexes rebuilt in parallel on initialization:

// src/brainy.ts:init()
async init(): Promise<void> {
  // Check if indexes are empty
  const metadataEmpty = await this.metadataIndex.isEmpty()
  const hnswEmpty = await this.index.isEmpty()
  const graphEmpty = await this.graphIndex.isEmpty()

  if (metadataEmpty || hnswEmpty || graphEmpty) {
    // Rebuild all indexes in parallel
    await Promise.all([
      metadataEmpty ? this.metadataIndex.rebuild() : Promise.resolve(),
      hnswEmpty ? this.index.rebuild() : Promise.resolve(),
      graphEmpty ? this.graphIndex.rebuild() : Promise.resolve()
    ])
  }
}

Triple Intelligence Integration

The TripleIntelligenceSystem (src/cortex/tripleIntelligence.ts) combines all three core indexes:

class TripleIntelligenceSystem {
  constructor(
    private metadataIndex: MetadataIndexManager,
    private hnswIndex: HNSWIndex,
    private graphIndex: GraphAdjacencyIndex,
    private embedder: EmbedderFunction,
    private storage: BaseStorage
  ) {}

  async query(nlpQuery: string): Promise<Result[]> {
    // Parse natural language
    const parsed = await this.parseQuery(nlpQuery)

    // Execute across all three indexes
    const [metadataResults, vectorResults, graphResults] = await Promise.all([
      this.metadataIndex.getIdsForFilter(parsed.filters),
      this.hnswIndex.search(parsed.vector, parsed.limit),
      this.graphIndex.traverse(parsed.graphConstraints)
    ])

    // Fuse results with weighted scoring
    return this.fuseResults(metadataResults, vectorResults, graphResults)
  }
}

Performance Characteristics

Operation Complexity by Index

Operation	MetadataIndex	HNSWIndex	GraphAdjacencyIndex	DeletedItemsIndex
Add	O(1) per field	O(log n)	O(1)	O(1)
Remove	O(1) per field	O(log n)	O(1)	O(1)
Exact lookup	O(1)	N/A	O(1)	O(1)
Range query	O(log n) + O(k)	N/A	N/A	N/A
Similarity search	N/A	O(log n)	N/A	N/A
Neighbor lookup	N/A	N/A	O(1)	N/A
Statistics	O(1)	O(1)	O(1)	O(1)

Where:

• n = total number of entities
• k = number of matching results

Memory Footprint

Index	Per-Entity Memory	Notes
MetadataIndex	~100 bytes	Depends on field count and cardinality
HNSWIndex	~1.5 KB	Vector (384 dims × 4 bytes) + graph connections
GraphAdjacencyIndex	~50 bytes per relationship	Bidirectional references + metadata
DeletedItemsIndex	~40 bytes per deleted ID	Just Set storage

Total overhead: ~1.6 KB per entity + ~50 bytes per relationship

Scalability

All indexes scale gracefully:

Database Size	Metadata Filter	Vector Search	Graph Hop	Combined Query
1K entities	0.3ms	0.8ms	0.05ms	1.1ms
10K entities	0.5ms	1.2ms	0.08ms	1.5ms
100K entities	0.8ms	1.8ms	0.1ms	2.1ms
1M entities	1.2ms	2.5ms	0.1ms	2.8ms

Key observations:

• Graph queries stay O(1) regardless of scale
• Metadata filtering scales sub-linearly
• Vector search degrades gracefully due to HNSW
• Combined queries remain fast even at scale

Best Practices

When to Use Each Index

MetadataIndex:

• Filtering by exact field values (status, type, category)
• Range queries on numeric/temporal fields (dates, prices, counts)
• Field discovery (what filters are available)
• Type-based querying (find all characters, all items)

HNSWIndex:

• Semantic similarity search ("find similar documents")
• Content-based retrieval ("find posts about AI")
• Fuzzy matching (when exact matches aren't required)
• Recommendation systems (find related items)

GraphAdjacencyIndex:

• Relationship queries ("who knows whom")
• Path finding ("how are these entities connected")
• Network analysis ("find communities")
• Multi-hop traversal ("friends of friends")

DeletedItemsIndex:

• Soft deletes (preserve data but hide from queries)
• Audit trails (track what was deleted when)
• Restoration workflows (undo deletions)

Query Optimization

1. Start with metadata filters - They're fastest and most selective
2. Use graph constraints - O(1) lookups significantly reduce search space
3. Vector search last - Most expensive, best used on pre-filtered set
4. Leverage temporal bucketing - Timestamp range queries work efficiently
5. Monitor statistics - Use O(1) stats methods for cardinality estimation

Memory Management

1. Configure UnifiedCache appropriately - Balance between speed and memory
2. Use lazy loading - HNSW loads vectors on-demand
3. Monitor cache hit rates - Adjust cache size if hit rate is low
4. Consider storage adapter - Memory storage = fastest, S3 = most scalable

Related Documentation

• Find System - Query-centric view of index usage
• Triple Intelligence - Advanced query system
• Storage Architecture - Storage layer details
• Performance Guide - Performance tuning
• Overview - High-level architecture

Version History

• v3.41.0 (October 2025): Added automatic temporal bucketing to MetadataIndex
• v3.40.0 (October 2025): Enhanced batch processing for imports
• v3.0.0 (September 2025): Introduced 4-index architecture with UnifiedCache