Investigate latency on tiered requests

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.

The 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.

To check whether the slow requests are the ones going through Tiered Cache:

1. Open Log Explorer 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.

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.

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: selects upper tiers using origin-latency data, which can route around a slow upper-tier-to-origin path automatically.
• Custom Tiered Cache: lets you work with your account team to design a topology that avoids specific upper-tier data centers.

• Investigate uncached responses
• Tiered Cache
• HTTP Requests log fields