--- description: Identify whether intermittent request slowness correlates with Tiered Cache upper-tier routing, and collect the evidence needed to report it. title: Investigate latency on tiered requests image: https://developers.cloudflare.com/cache/troubleshooting/investigating-tiered-cache-latency/og.png?v=024c14715f0d8280 --- [Skip to content](#main-content) > Documentation Index > Fetch the complete documentation index at: https://developers.cloudflare.com/cache/llms.txt > Use this file to discover all available pages before exploring further. # Investigate latency on tiered requests Last updated Sep 29, 2026|Copy as Markdown| [View as Markdown](https://developers.cloudflare.com/cache/troubleshooting/investigating-tiered-cache-latency/index.md)| [Agent setup](https://developers.cloudflare.com/agent-setup/) Some requests for the same URL are slow while others are fast. If the slow requests have a `cf-cache-status` of `MISS` or `EXPIRED` and the fast requests have `HIT`, the difference may be explained by Tiered Cache: slow requests miss in the lower-tier data center and fetch through an upper-tier data center before reaching your origin. Fast requests are served directly from the lower-tier cache. This page describes how to use Log Explorer to confirm whether Tiered Cache is involved and how to collect the data needed before contacting Support. ## Confirm Tiered Cache routing with Log Explorer The [HTTP Requests](https://developers.cloudflare.com/logs/logpush/logpush-job/datasets/zone/http_requests/) dataset exposes fields that show whether a request was routed through an upper tier: - **`CacheTieredFill`**: `true` when the lower-tier data center fetched from an upper-tier data center for this request. - **`EdgeColoCode`**: the IATA airport code for the lower-tier data center that received the request. - **`UpperTierColoID`**: the internal ID of the upper-tier data center used for the fill. - **`CacheCacheStatus`**: the cache outcome ( `HIT`, `MISS`, `EXPIRED`, `BYPASS`, and so on). - **`OriginResponseDurationMs`**: the total time from when the lower-tier sent a request upstream until it received the full response. When `CacheTieredFill` is `true`, this duration includes the upper-tier lookup, any transit to your origin (also includes Argo Smart Routing transit time, if enabled), origin processing, and the response back. It is a measure of correlation, not isolation of a specific network hop. ## Correlate slow requests with upper-tier usage To check whether the slow requests are the ones going through Tiered Cache: 1. Open [Log Explorer](https://developers.cloudflare.com/logs/) for the zone. 2. Filter by the affected URL or path and set a time window that includes both slow and fast samples. 3. Group by `CacheTieredFill` and compare `OriginResponseDurationMs` between the two groups. If requests where `CacheTieredFill` is `true` show significantly higher `OriginResponseDurationMs` than those where it is `false`, Tiered Cache routing is correlated with the slowness. 4. Note the `EdgeColoCode` values for the slow requests and the `UpperTierColoID` values. These identify which lower-tier and upper-tier pair is involved. Note `OriginResponseDurationMs` captures total upstream response time across all hops. It does not isolate a specific segment, such as transit between the upper tier and your origin, and does not prove congestion on a particular path. Use it to establish whether Tiered Cache routing correlates with the slow samples before escalating. ## What to bring to Support When you contact Cloudflare Support, include: - The zone ID and affected URL or path. - A Log Explorer export or screenshot showing slow samples ( `CacheTieredFill: true`) and fast samples ( `CacheTieredFill: false`), with `OriginResponseDurationMs`, `EdgeColoCode`, `UpperTierColoID`, and `CacheCacheStatus` visible. - The time window in UTC during which you observed the issue. Cloudflare Support and network engineering use this data to assess whether a routing change between the upper-tier data center and your origin is needed. ## Why turning off Tiered Cache does not fix the underlying cause Turning off Tiered Cache routes all cache misses from every lower-tier data center directly to your origin. If the underlying issue is a congested or slow path from a specific upper-tier data center to your origin, turning off Tiered Cache may redistribute traffic rather than resolve the congestion, and removes the cache-fill efficiency benefits for the rest of your traffic. If a specific upper-tier data center consistently produces high `OriginResponseDurationMs`, the appropriate fix is a routing or topology change. Consider: - **[Smart Tiered Cache](https://developers.cloudflare.com/cache/how-to/tiered-cache/#smart-tiered-cache)**: selects upper tiers using origin-latency data, which can route around a slow upper-tier-to-origin path automatically. - **[Custom Tiered Cache](https://developers.cloudflare.com/cache/how-to/tiered-cache/#custom-tiered-cache)**: lets you work with your account team to design a topology that avoids specific upper-tier data centers. ## Related resources - [Investigate uncached responses](https://developers.cloudflare.com/cache/troubleshooting/investigating-uncached-responses/) - [Tiered Cache](https://developers.cloudflare.com/cache/how-to/tiered-cache/) - [HTTP Requests log fields](https://developers.cloudflare.com/logs/logpush/logpush-job/datasets/zone/http_requests/) Was this helpful? 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