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DGraph, a C++ recommendation engine launched in 2022 for 得物, combines an index layer with a service layer, uses lock‑free RCU structures, a custom mmap‑based D‑Allocator, RoaringBitmap invert indexes, and a multi‑operator fusion scheduler to achieve high‑performance, eventually consistent, scalable recommendations.
Linux kernel synchronization requires protecting shared mutable state from concurrent access using primitives such as spinlocks, mutexes, read‑write locks, or lock‑less techniques like RCU, which copies data and waits for a grace period, each offering distinct performance, latency, and complexity trade‑offs.
The Linux kernel’s page‑cache indexing migrated from the classic radix‑tree structure—using shift‑based multi‑way nodes, RCU‑protected insert, lookup, and delete operations—to the newer XArray API introduced in 4.20, which retains the radix layout while offering automatic resizing, built‑in locking, richer marking, and a cleaner, safer interface.