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plugin/cache: clarify stale verify behavior (#8579)

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Signed-off-by: git-jxj <65210887+git-jxj@users.noreply.github.com>
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jxj
2026-10-15 16:05:21 +08:00
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1 changed files with 5 additions and 3 deletions
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plugin/cache/README.md vendored
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@@ -68,11 +68,13 @@ cache [TTL] [ZONES...] {
available as long as it has not been expired for longer than **DURATION** (default 1 hour). By default, the _cache_ plugin will
attempt to refresh the cache entry after sending the expired cache entry to the client. The
responses have a TTL of 0 by default for backward compatibility. **REFRESH_MODE** controls the timing of the expired cache entry refresh.
`verify` will first verify that an entry is still unavailable from the source before sending the expired entry to the client.
For a request that starts its own refresh, `verify` checks the source before sending a stale entry.
If it receives an accepted updated response, that request uses the update. A positive **VERIFY_TIMEOUT**
permits the request to fall back to the stale entry when the wait expires. A positive **FAILURE_RECHECK**
lets concurrent requests return stale immediately while a verify is in flight, even if that verify later succeeds.
`immediate` will immediately send the expired entry to the client before
checking to see if the entry is available from the source. **REFRESH_MODE** defaults to `immediate`. Setting this
value to `verify` can lead to increased latency when serving stale responses, but will prevent stale entries
from ever being served if an updated response can be retrieved from the source.
value to `verify` can lead to increased latency for requests that wait for an upstream refresh.
In `immediate` mode, concurrent requests for the same expired entry dispatch at most one
background refresh.
**VERIFY_TIMEOUT** is only valid with `verify` and bounds how long the cache waits for the upstream