docs(adr): memory + eviction decisions 0006-0008 (closes #41, #45, #46)#171
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ADR-0006 default allocator (#41): tikv-jemallocator/jemalloc for mallctl introspection, the je_get_defrag_hint path, and tuned dirty-page decay; per-shard mallctl accounting makes maxmemory honest (invariant 3); mimalloc rejected as default for lacking introspection/defrag-hint. ADR-0007 cache mode by default (#45): host-derived ceiling + eviction ON; strict no-evict is an explicit opt-in, inverting Redis's maxmemory 0 / noeviction footgun. ADR-0008 default eviction policy (#46): S3-FIFO behind a pluggable EvictionPolicy trait; SIEVE and W-TinyLFU-fronted kept selectable; LRU rejected (per-hit relink). INDEX/OPEN/QUESTIONS updated; #42/#47 to be re-milestoned to M1 as empirical validation. Closes #41 Closes #45 Closes #46 Signed-off-by: Zeke <ezequiel.lares@outlook.com>
ADR-0006: correct the accounting model (jemalloc stats.allocated is logical used_memory, NOT RSS; invariant 3 means logical allocated bytes; RSS can exceed it, decay/defrag keep them close); record #41's commitments to enable the jemalloc background purger and lower dirty_decay_ms for eviction churn; narrow the mimalloc rejection to the decisive je_get_defrag_hint gap (mimalloc can report RSS via mi_process_info). ADR-0007: replace the strawman rejected option with issue #45's real Option C (ceiling-on + noeviction default). ADR-0008: cite SIEVE's own >45%-of-traces result and the ~8B/entry W-TinyLFU sketch vs S3-FIFO's 2-bit counter; flag both win-rates as home-corpus, gated on #47; add the sampled-LRU/LFU rejection. refs #41, refs #45, refs #46 Signed-off-by: Zeke <ezequiel.lares@outlook.com>
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Three evidence-grounded decisions on the bytes-per-key / throughput-per-core core.
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Review focus (engineering)
Closes #41. Closes #45. Closes #46. Part of M0: Vision and Scope.