Mythosia.VectorDb.InMemory 4.1.0

Mythosia.VectorDb.InMemory

Package Summary

Provides InMemoryVectorStore, a thread-safe in-memory implementation of IVectorStore using cosine similarity search.
Suitable for development, testing, and small-scale workloads.

Usage

Automatically used as the default vector store in Mythosia.AI.Rag:

// Explicit selection (same as default)
.WithRag(rag => rag
 .AddDocument("docs.txt")
 .UseInMemoryStore()
)

Features

• Thread-safe — Uses ConcurrentDictionary for safe concurrent access
• Cosine similarity — TopK search with configurable result count
• Hybrid search — BM25 + dense vector fusion via weighted RRF, scores normalized to [0, 1]
• Metadata filtering — Full VectorFilter operator set (Eq/Ne/In/NotIn/Gt/Gte/Lt/Lte/Like/Exists/NotExists, And/Or groups)
• Minimum score — Discard results below a similarity threshold
• Upsert — Single and batch upsert operations
• CountAsync — Count records, optionally narrowed by filter criteria
• Diagnostics — IRagDiagnosticsStore: ListAllRecordsAsync, ScoredListAsync, GetTotalRecordCount

Standalone Usage

Recommended — Metadata-based isolation

using Mythosia.VectorDb;
using Mythosia.VectorDb.InMemory;

var store = new InMemoryVectorStore();

await store.UpsertAsync(new VectorRecord
{
 Id = "doc-1",
 Content = "Some text content",
 Vector = new float[] { 0.1f, 0.2f, 0.3f },
 Metadata =
 {
 ["source"] = "manual.txt",
 ["namespace"] = "my-namespace",
 ["scope"] = "tenant-1"
 }
});

var filter = new VectorFilter()
 .Where("namespace", "my-namespace")
 .Where("scope", "tenant-1");
var results = await store.SearchAsync(queryVector, topK: 5, filter: filter);

BM25 Index

Bm25Index provides in-memory BM25 keyword search for hybrid retrieval. When UseHybridSearch() is called with InMemoryVectorStore, the RAG pipeline automatically builds a BM25 index alongside the vector store and merges results via RRF.

// Automatic — just enable hybrid search in the builder
var store = await RagStore.BuildAsync(config => config
 .AddText("환불은 14일 이내 가능합니다.", id: "refund")
 .UseLocalEmbedding(512)
 .UseInMemoryStore()
 .UseHybridSearch() // BM25 index is built automatically
);

Standalone usage:

using Mythosia.VectorDb.InMemory;

var bm25 = new Bm25Index();
bm25.Index("doc1", "machine learning neural network");
bm25.Index("doc2", "cooking recipe pasta");

var results = bm25.Search("machine learning", topK: 5);
// results[0].Id == "doc1", results[0].Score > 0

When hybrid search is used, fused RRF scores are normalized to the [0, 1] range so VectorFilter.MinScore is applied consistently to the final merged score.

VectorFilter

For the full operator reference and fluent API examples (Where, WhereNot, WhereIn, WhereLike, WhereExists, Or, And, WithMinScore, etc.), see the .

InMemory-specific note: Range operators (WhereGreaterThan, WhereLessThan, etc.) use string.Compare (ordinal). Store numeric values zero-padded (e.g. "0042") for correct ordering.

Batch Get & Count

// Fetch multiple records by ID in one call
var filter = new VectorFilter().Where("namespace", "docs");
var records = await store.GetBatchAsync(new[] { "id-1", "id-2", "id-3" }, filter);

// Count all records matching a filter
long count = await store.CountAsync(new VectorFilter().Where("namespace", "docs"));

// Count with additional metadata filter
long filtered = await store.CountAsync(
 new VectorFilter().Where("namespace", "docs").Where("storage_id", storageId));

GetBatchAsync performs O(1)-per-ID lookups via ConcurrentDictionary.TryGetValue — no vector scoring, just direct key access. Records not found or not matching the filter are omitted.

Resource Disposal

InMemoryVectorStore implements IDisposable. A Bm25Index (Lucene writer, analyzer, RAMDirectory) is maintained alongside the vector store. Dispose the store when it is no longer needed to release these resources:

using var store = new InMemoryVectorStore();
// ... use store
// Lucene resources released on Dispose

Vector Replacement

ReplaceByFilterAsync is available via the IVectorStore default interface method. It performs sequential DeleteByFilterAsync → UpsertBatchAsync (non-transactional, suitable for in-memory usage):

IVectorStore store = new InMemoryVectorStore();

var filter = new VectorFilter()
 .Where("full_path", "/docs/file.md");

await store.ReplaceByFilterAsync(filter, newRecords);

For transactional guarantees (zero query gap), use PostgresStore which wraps both operations in a single database transaction.

Limitations

• Data is not persisted — lost when the process exits
• Not suitable for large-scale production workloads (millions of vectors)
• For persistence or scale, implement a custom IVectorStore (e.g., Qdrant, Chroma, Pinecone)