qdrant-sliding-time-window

# Scaling with a Sliding Time Window

Use when only recent data needs fast search -- social media posts, news articles, support tickets, logs, job listings. Old data either becomes irrelevant or can tolerate slower access.

Three strategies: **shard rotation** (recommended), **collection rotation** (when per-period config differs), and **filter-and-delete** (simplest, for continuous cleanup).


## Shard Rotation (Recommended)

Use when: data has natural time boundaries (daily, weekly, monthly). Preferred because queries span all time periods in one request without application-level fan-out. [User-defined sharding](https://search.qdrant.tech/md/documentation/operations/distributed_deployment/?s=user-defined-sharding)

1. Create a collection with user-defined sharding enabled
2. Create one shard key per time period (e.g., `2025-01`, `2025-02`, ..., `2025-06`)
3. Ingest data into the current period's shard key
4. When a new period starts, create a new shard key and redirect writes
5. Delete the oldest shard key outside the retention window

- Deleting a shard key reclaims all resources instantly (no fragmentation, no optimizer overhead)
- Pre-create the next period's shard key before rotation to avoid write disruption
- Use `shard_key_selector` at query time to search only specific periods for efficiency
- Shard keys can be placed on specific nodes for hot/cold tiering


## Collection Rotation (Alias Swap)

Use when: you need per-period collection configuration (e.g., different quantization or storage settings). [Collection aliases](https://search.qdrant.tech/md/documentation/manage-data/collections/?s=collection-aliases)

1. Create one collection per time period, point a write alias at the newest
2. Query across all active collections in parallel, merge results client-side
3. When a new period starts, create the new collection and swap the write alias [Switch collection](https://search.qdrant.tech/md/documentation/manage-data/collections/?s=switch-collection)
4. Drop the oldest collection outside the window

Trade-off vs shard rotation: allows per-collection config differences, but requires application-level fan-out and more operational overhead.


## Filter-and-Delete

Use when: data arrives continuously without clear time boundaries, or you want the simplest setup.

1. Store a `timestamp` payload on every point, create a payload index on it [Payload index](https://search.qdrant.tech/md/documentation/manage-data/indexing/?s=payload-index)
2. Filter to the desired window at query time using `range` condition [Range filter](https://search.qdrant.tech/md/documentation/search/filtering/?s=range)
3. Periodically delete expired points using delete-by-filter [Delete points](https://search.qdrant.tech/md/documentation/manage-data/points/?s=delete-points)

- Run cleanup during off-peak hours in batches (10k-50k points) to avoid optimizer locks
- Deletes are not free: tombstoned points degrade search until optimizer compacts segments
- Does not reclaim disk instantly (compaction is asynchronous)


## Hot/Cold Tiers

Use when: recent data needs fast in-RAM search, older data should remain searchable at lower performance.

- **Shard rotation:** place current shard key on fast-storage nodes, move older shard keys to cheaper nodes via shard placement. All queries still go through a single collection.
- **Collection rotation:** keep current collection in RAM (`always_ram: true`), move older collections to mmap/on-disk vectors. [Quantization](https://search.qdrant.tech/md/documentation/manage-data/quantization/)


## What NOT to Do

- Do not use filter-and-delete for high-volume time-series with millions of daily deletes (use rotation instead)
- Do not forget to index the timestamp field (range filters without an index cause full scans)
- Do not use collection rotation when shard rotation would suffice (unnecessary fan-out complexity)
- Do not drop a shard key or collection before verifying its period is fully outside the retention window
- Do not skip pre-creating the next period's shard key or collection (write failures during rotation are hard to recover)