Optimistically cache mapped metadata when cluster metadata is periodically refreshed #725
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In Mimir, we have a process creating 1
Client
(settingMetadataMinAge
= MetadataMaxAge = 10s`) and then using it to do two things:ListOffsets
every 1sI noticed that such
Client
issues 2Metadata
requests everyMetadataMinAge
(remember that we setMetadataMaxAge = MetadataMinAge
).One request is due to the periodic Metadata refresh, and one is due to
ListOffsets
which needMetadata
as well.ListOffsets
request callsClient.fetchMappedMetadata()
which caches the metadata forMetadataMinAge
, so effectively leading to 2Metadata
requests everyMetadataMinAge
.In this PR I'm proposing to optimistically cache the mapped metadata when cluster metadata is periodically refreshed.
Notes
fetchMappedMetadata()
comment says "this is garbage heavy, so it is only used in one off requests in this package". Part of the the garbage is introduced by caching the mapped metadata, which is now done each time metadata is refreshed. Do you see any issue?storeCachedMappedMetadata()
, but I haven't come up with a better idea which either doesn't make code more complex or introduce more allocations. Thoughts?Metadata
requests dropped from 2 to 1 everyMetadataMinAge