ClickHouse Release 26.6

Summary

ClickHouse 26.6 is a release marking the 10-year anniversary of ClickHouse becoming open source, with 56 new features, 79 performance optimizations, and 366 bug fixes. Hypothetical skip indexes let users evaluate set indexes in a session without building them; on a 487.24-million-row UK property dataset, the example estimated skip ratios of 77.0% at granularity 128 and 92.2% at granularity 1. The release overhauls dependencies between refreshable materialized views, addressing schedule drift that could make dependent stages lag or miss a refresh cycle. It also introduces experimental continuous queries, the aiEmbed function, embedding quantization to 8 bits and below, and workload-level memory reservations.

Takeaways

1. 1

   Hypothetical skip indexes are visible only in the current session, are discarded when it ends, and let EXPLAIN WHATIF estimate applicability, bytes read, marks scanned, and skip ratio before an index is built.

2. 2

   On the example UK property dataset, a set index on town was estimated to skip 77.0% of granules at granularity 128 and 92.2% at granularity 1.

3. 3

   Embedding components can be quantized to 8 bits and below; the post states this could shrink vector indexes fourfold or more, while memory reservations can be assigned through workload settings.