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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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parent 9d1343c54c
commit 25b51bcbd9
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 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 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. 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 `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 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 value to `verify` can lead to increased latency for requests that wait for an upstream refresh.
from ever being served if an updated response can be retrieved from the source.
In `immediate` mode, concurrent requests for the same expired entry dispatch at most one In `immediate` mode, concurrent requests for the same expired entry dispatch at most one
background refresh. background refresh.
**VERIFY_TIMEOUT** is only valid with `verify` and bounds how long the cache waits for the upstream **VERIFY_TIMEOUT** is only valid with `verify` and bounds how long the cache waits for the upstream