mirror of
https://github.com/scylladb/scylladb.git
synced 2026-06-04 14:03:06 +00:00
c95dd67d11
It is a read-through cache of a file. Will be used to cache contents of the promoted index area from the index file. Currently, cached pages are evicted manually using the invalidate_*() method family, or when the object is destroyed. The cached_file represents a subset of the file. The reason for this is to satisfy two requirements. One is that we have a page-aligned caching, where pages are aligned relative to the start of the underlying file. This matches requirements of the seastar I/O engine on I/O requests. Another requirement is to have an effective way to populate the cache using an unaligned buffer which starts in the middle of the file when we know that we won't need to access bytes located before the buffer's position. See populate_front(). If we couldn't assume that, we wouldn't be able to insert an unaligned buffer into the cache.