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When is data written to cache in the Write-around cache?

When is data written to cache in the Write-around cache?..The course is confusing! Can anyone please help.

In a write-around cache data is written to backend DB/datastore only in a write operation. Cache only receives data when a clients read request asks for the record/data. On first read request of a record data is loaded to cache as well. First read request of the record is slow for the client, but subsequent read requests will be served form the cache. From there on whether the record remain in cache or not depends on Cache retention policy, such as TTL, LRU etc.

@Design_Gurus Can you please answer when is data written to cache ? Does the server update the dirty bit in cache to invalidate it ?