--- title: Cloudflare Identifies Query Planning Bottleneck in... description: Cloudflare traced a slowdown in its billing pipeline to lock contention inside ClickHouse's query planning stage. After migrating to a per-tenant partitioning... canonical: https://daily.dev/posts/cloudflare-identifies-query-planning-bottleneck-in-clickhouse-2yvq0qcqd twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Cloudflare Identifies Query Planning Bottleneck in ClickHouse | daily.dev og:description: Cloudflare traced a slowdown in its billing pipeline to lock contention inside ClickHouse's query planning stage. After migrating to a per-tenant partitioning... og:url: https://daily.dev/posts/cloudflare-identifies-query-planning-bottleneck-in-clickhouse-2yvq0qcqd og:image: https://api.daily.dev/og/posts/2YVQ0qcqd.png og:image:alt: Cloudflare Identifies Query Planning Bottleneck in ClickHouse og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Cloudflare Identifies Query Planning Bottleneck in ClickHouse **[InfoQ](https://daily.dev/sources/infoq)** · 4 min read · 0 upvotes · 0 comments ## Summary Cloudflare traced a slowdown in its billing pipeline to lock contention inside ClickHouse's query planning stage. After migrating to a per-tenant partitioning scheme, the number of data parts grew significantly, causing 45% of CPU time to be spent in a single function (filterPartsByPartition) waiting to acquire an exclusive mutex (MergeTreeData). The team patched ClickHouse by replacing the exclusive lock with a shared lock, removing the per-query copy of the full parts list, and improving part filtering. After deploying the patch in March 2026, query durations dropped by 50% and performance no longer correlated with part count growth. The changes were contributed upstream and are available in ClickHouse version 25.11. Long-term sustainability of the architecture remains uncertain as metadata load continues to grow. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [Our billing pipeline was suddenly slow. The culprit was a hidden bottleneck in ClickHouse](https://daily.dev/posts/our-billing-pipeline-was-suddenly-slow-the-culprit-was-a-hidden-bottleneck-in-clickhouse-t6saatu35) · Cloudflare · 7 upvotes · 0 comments - [Running out of runway: migrating Temporal Cloud's billing store to ClickHouse](https://daily.dev/posts/running-out-of-runway-migrating-temporal-cloud-s-billing-store-to-clickhouse-rpxl3uwjt) · Temporal · 0 upvotes · 0 comments --- Tags: [#cloudflare](https://daily.dev/tags/cloudflare), [#clickhouse](https://daily.dev/tags/clickhouse) [View this post on daily.dev](https://daily.dev/posts/cloudflare-identifies-query-planning-bottleneck-in-clickhouse-2yvq0qcqd) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Cloudflare Identifies Query Planning Bottleneck in ClickHouse","url":"https://daily.dev/posts/cloudflare-identifies-query-planning-bottleneck-in-clickhouse-2yvq0qcqd","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/cloudflare-identifies-query-planning-bottleneck-in-clickhouse-2yvq0qcqd"},"datePublished":"2026-06-06T05:03:40.342Z","dateModified":"2026-06-06T05:04:00.389Z","description":"Cloudflare traced a slowdown in its billing pipeline to lock contention inside ClickHouse's query planning stage. 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