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chore: don't cache errors in file cache#18555
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| } | ||
| func(c*Cache)registerMetrics(registerer prometheus.Registerer)*Cache { | ||
| funcnewCacheMetrics(registerer prometheus.Registerer)cacheMetrics { |
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👍
| // Check if the caller's context was canceled | ||
| iferr:=ctx.Err();err!=nil { | ||
| returnnil,err |
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Why do we need to check this? It will fail theAuthorize if it is cancelled
And if we do this check, do we need to close?
| // Check if the caller's context was canceled | |
| iferr:=ctx.Err();err!=nil { | |
| returnnil,err | |
| // Check if the caller's context was canceled | |
| iferr:=ctx.Err();err!=nil { | |
| e.close() | |
| returnnil,err |
| // Check that the caller is authorized to access the file | ||
| subject,ok:=dbauthz.ActorFromContext(ctx) | ||
| if!ok { | ||
| returnnil,dbauthz.ErrNoActor | ||
| } |
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Need to close?
| // Check that the caller is authorized to access the file | |
| subject,ok:=dbauthz.ActorFromContext(ctx) | |
| if!ok { | |
| returnnil,dbauthz.ErrNoActor | |
| } | |
| // Check that the caller is authorized to access the file | |
| subject,ok:=dbauthz.ActorFromContext(ctx) | |
| if!ok { | |
| e.close() | |
| returnnil,dbauthz.ErrNoActor | |
| } |
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By design, concurrent calls to
Acquirein the file cache all share a single database fetch. This is by design, so that everyone can share in the success of whoever asked for the file first. That's kind of what caches do!but one problem with the current implementation is that errors are also shared. This is mostly fine, because once all of the references are dropped, the cache entry will be freed, and the next
Acquirewill trigger a new fetch. However, if enough people are trying to load the same file at once, you could imagine how they might keep retrying and the reference count neverquite hits zero.To combat this, just immediately and forcibly remove errors from the cache, even if they still have references. Whoever is the first to retry afterwards will trigger a new fetch (like we want), which can then again be shared by others who retry.
Related, one opportunity to reduce the potential for errors we have is to use
context.Background()for the database fetch so that a canceled request context cannot disrupt others who may be waiting for the file. We can then manually check the context outside of theLoad, just like we already do with authorization.