🧱 2 MB Megaslab Memory Engine

The kachedb-core memory subsystem completely eliminates runtime malloc and free allocation jitter by managing storage through structured 2 MB Megaslabs with 64-byte L1 CPU cache-line alignment.

📐 Memory Slab Geometry

┌────────────────────────────────────────────────────────────────────────────────────────┐
│                        2 MB Megaslab Page Frame (2,097,152 Bytes)                      │
│ ┌───────────────────┬───────────────────┬───────────────────┬────────────────────────┐ │
│ │  Slot 0 (64B-Aln) │  Slot 1 (64B-Aln) │  Slot 2 (64B-Aln) │  Slot N (64B-Aln)      │ │
│ │ [ Payload Data  ] │ [ Payload Data  ] │ [ Payload Data  ] │ [ Payload Data  ]      │ │
│ └───────────────────┴───────────────────┴───────────────────┴────────────────────────┘ │
└────────────────────────────────────────────────────────────────────────────────────────┘

1. Cache-Line Alignment (`64-byte`)

Every allocated slot is guaranteed to start on a 64-byte boundary via libc::posix_memalign.
Zero False Sharing: Multi-core writes to neighboring slots never cross CPU L1 cache line boundaries, eliminating cache invalidation stalls.

2. Standard Size Classes

Class Name	Slot Size	Slots per 2 MB Megaslab	Primary Workload
`AppSmall`	128 Bytes	16,384	Session IDs, token auths, atomic counters, short strings
`AppMedium`	512 Bytes	4,096	JSON user profiles, metadata records
`AppLarge`	4,096 Bytes (4 KB)	512	Large document blobs, web cache pages
`Tensor64KB`	65,536 Bytes (64 KB)	32	LLM KV attention block (16 tokens FP16)
`Tensor256KB`	262,144 Bytes (256 KB)	8	LLM KV attention block (64 tokens BF16)

⚡ Bump Pointer + Free-List Recycling

Allocation in KacheDB occurs in two stages:

Fast-Path Bump Allocation: If the active 2 MB arena has unallocated capacity, it increments a local cursor in $\approx 3.84\text{ ns}$.
Free-List Slot Recycling: When keys are overwritten, deleted, or expired, their BlockId is pushed to a lock-free LIFO free-list for immediate O(1) slot reuse.

🔄 Dynamic S3-FIFO Workload Quotas

KacheDB implements the state-of-the-art S3-FIFO (Simple, Scalable, Small-footprint FIFO) cache eviction algorithm:

Small Queue (10% capacity): Acts as a high-speed filter against scan pollution and one-off burst keys.
Main Queue (90% capacity): Stores frequency-accessed keys with multi-chance bit tracking.
Ghost Queue: Tracks key signatures after eviction to detect re-access and promote directly into the Main Queue.
Elastic Borrowing: The WorkloadQuota manager balances memory pools between Redis key-value workloads and LLM tensor memory elastically.

KacheDB Documentation