When a Shared Proxy Cache Helps a Crawler
Evaluate repeated resources, freshness and actual crawler fetches before expecting a shared forward-proxy cache to improve throughput.
Suppose several browser-based workers open different pages from one site. Those pages reference the same stylesheet, logo and script bundle. A shared forward cache can make the first fetch useful to later workers when the responses are reusable.
Now change the workload: each worker downloads only one HTML document and never loads its linked resources. The common stylesheet is still present in the markup, but no worker requests it. It contributes nothing to the proxy’s cache hit rate.
Start with the requests your crawler actually makes
A browser rendering a page and an HTTP client retrieving its source create different request sets. Inspect those sets before choosing a caching design.
| Workload | Potential for shared reuse |
|---|---|
| Workers repeatedly fetch the same public assets | Useful when freshness and cache-key rules permit it |
| Every request has a unique URL or response variant | Little overlap to reuse |
| A response needs revalidation before reuse | May save response bytes while still needing an upstream round trip |
| Workers already satisfy requests from their own local cache | Those requests may never reach the shared proxy |
URL equality alone is insufficient. The response’s freshness policy and fields named by Vary can distinguish representations. Private, non-storable or authenticated content needs the applicable shared-cache rules; it should not be forced into one public result just to raise the hit count.
For ordinary HTTPS CONNECT traffic, the forward proxy carries an encrypted tunnel and has no HTTP objects inside it to cache. A TLS-inspection deployment has different trust and processing behavior. Include the actual mode when assessing whether object caching is available.
A cache hit can avoid an upstream fetch, while a miss still pays for the intermediary’s work. Compare completed useful bytes, upstream traffic and latency for the intended workload. Thread count describes concurrency; it does not describe how much reusable content those threads share.