# Netflix/hollow

Hollow is a java library and toolset for disseminating in-memory datasets from a single producer to many consumers for high performance read-only access.

Repository: https://github.com/Netflix/hollow
Canonical: https://ross.abutalabs.com/products/hollow
Language: Java
License: Apache-2.0
License Family: permissive
Last push: 2026-08-25T23:36:24+00:00

## Health v2 (maintenance only)
Score: 95/100 (v2, computed 2026-09-03T02:39:23.370411+00:00)
- activity 99, release rhythm 87, longevity 100
- inputs: {"age_days": 3561, "days_push": 8, "days_rel": 8, "gap_med": 6.0, "n_releases_24m": 71}
- flags: none
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 1366, forks 248 (observed 2026-08-28T04:04:31.259014+00:00)

## What it is
Hollow is a Java library and toolset for disseminating in-memory datasets from a single producer to many consumers for high-performance read-only access. It enables efficient snapshot and delta-based data distribution across services.

## Use cases
- distribute reference data from one producer to many microservices
- serve large read-only in-memory datasets with low latency
- incrementally update consumers with dataset deltas
- broadcast lookup data like movie titles or product catalogs to edge services
- replace repeated database queries with in-memory read-only datasets

## When to choose
- you have one producer and many consumers of a mostly read-only dataset
- consumers need fast in-memory access without hitting a database
- you need incremental delta updates pushed to many services
- you run on the JVM and want a battle-tested Netflix OSS solution

## When to avoid
- your data is write-heavy or requires transactional updates
- consumers are not on the JVM
- your dataset is small enough to fit a simple cache or config file
- you need SQL query capabilities over the data

## Facets
- artifact type: library
- maturity: stable
- function: caching, serialization, database, streaming
- domain: microservices, backend, developer-tools
- platform: jvm, cross-platform
- tags: in-memory-dataset, read-only-access, data-dissemination, producer-consumer, netflix-oss, data-engineering

## Member repositories
- Netflix/hollow (main) score 95

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:04:31.259014+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-30T04:41:10.447542+00:00, confidence not recorded.
  - readme: https://github.com/Netflix/hollow (fetched 2026-08-28T04:04:31.259014+00:00, sha c15632230ecf)
- Data as of 2026-08-30T08:39:29.467469+00:00.