# Streaming secondary indices: incremental, demand-driven index evaluation

DevFeed: [Streaming secondary indices: incremental, demand-driven index evaluation](<https://devfeed.tech/articles/streaming-secondary-indices-incremental-demand-driven-index-evaluation-5580.md>)

Original publisher: [Read original article](<https://clickhouse.com/blog/streaming-secondary-indices>)

Author: Tom Schreiber

Published: 2026-01-12T00:00:00Z

Content type: article

Language: en

Sources: [ClickHouse Blog](<https://devfeed.tech/sources/clickhouse-blog.md>)

Topics: [clickhouse](<https://devfeed.tech/topics/clickhouse.md>), [Streaming](<https://devfeed.tech/topics/streaming.md>), [Latency](<https://devfeed.tech/topics/latency.md>), [data](<https://devfeed.tech/topics/data.md>)

Tags: [clickhouse](<https://devfeed.tech/tags/clickhouse.md>), [data](<https://devfeed.tech/tags/data.md>), [evaluation](<https://devfeed.tech/tags/evaluation.md>), [feature](<https://devfeed.tech/tags/feature.md>), [latency](<https://devfeed.tech/tags/latency.md>), [memory](<https://devfeed.tech/tags/memory.md>), [startup](<https://devfeed.tech/tags/startup.md>), [streaming](<https://devfeed.tech/tags/streaming.md>)

## AI overview

ClickHouse 25.9 introduces streaming secondary indices, evaluating index entries incrementally alongside table-data reads instead of scanning the entire secondary index upfront. This demand-driven approach reduces startup latency, unnecessary work, and memory usage, while allowing queries with LIMIT to stop without completing a full index scan.

## Source excerpt

ClickHouse now streams secondary index evaluation alongside data reads instead of scanning indexes upfront, making index usage incremental and demand-driven, reducing startup latency, unnecessary work, and memory usage.