retoorandClaude Sonnet 5
9dbd1fe667
- Plexer: always-active terminal multiplexing. NativePlexerController/ TmuxPlexerController share one interface, chosen by which env var is already set (TAI_PLEXER_SOCKET vs TMUX_PANE); NativePlexerBackend is the pty.fork()-based wrapper (raw mode, SIGWINCH resize forwarding, a Unix-socket control protocol, continuous session logging, a Ctrl+A prefix key distinct from tmux's own Ctrl+B). Auto-wraps new interactive shells via a .bashrc hook mirroring the existing command-not-found install pattern, gated on $TMUX/$TAI_PLEXER_ACTIVE/ a $HOME/.tai-no-plexer bypass. New plexer_send/read/type/status tools, env-gated on a detected controller. - tests/container.py + docker-compose.yml + tests/docker/Dockerfile: a disposable podman/docker image for the tests that must never touch a real machine (installing the plexer hook into a real ~/.bashrc, a live tmux session). Required suite (test_seal.py, test_tai.py, tests/plexer.py, tests/bashrc.py) gates the result; tests/rag.py runs as best-effort since its real-LLM dependency can't be satisfied inside a disposable container with no nested engine. - tests/bashrc.py: real end-to-end hook install + bash -i auto-wrap, anti-recursion, tmux-active skip, non-interactive skip, a live TmuxPlexerController test, and an install/uninstall round-trip. - tests/plexer.py: NativePlexerBackend under a real pty, plus a dedicated robustness pass (file permissions, >64KB payload framing, a malformed control request, a genuine self-deadlock fix in the write-to-child path). - tai_test.py: the shared async process-driving framework (pipe/pty transport, group-wide kill-and-reap, a StdinBridge for --interactive) both test files build on. - ChatClient last-resort backend: when there's no local opencode CLI but the sandbox box is already running, install opencode into it (official Node tarball, not apt -- apt's nodejs/npm pull in webpack/babel/jest as transitive deps) and route through it instead of giving up. Only reachable after the first retry round already failed everything else; never creates the box itself. TmuxPlexerController.status() fixed to use `list-panes` instead of `display-message -p`, which silently fell back to the default pane instead of erroring against a dead target. - Fix 4 pre-existing test_tai.py bugs surfaced by running it in a clean environment for the first time: two stale mock signatures (subprocess.run's stdout= kwarg, Chat.complete's deadline= kwarg), one $TMUX-dependent catalog assertion, one tty-dependent color assertion. - research/: a sourced research archive (Source Dossier/Citation Card/Conclusion tiers) backing the above design decisions, with its own audit.py consistency checker. - .gitignore: fix a blanket *.md rule that was about to silently drop the entire research/ archive from version control; add __pycache__/ and the one-off debug transcript this session started from. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
53 lines
3.0 KiB
Markdown
53 lines
3.0 KiB
Markdown
# 2Q Cache Management Algorithm
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## Metadata
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| Field | Value |
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| Institute | Molodetz Institute — Research & Retrieval Division |
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| Subject | agent-memory-recency-tracking |
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| Document type | Source Dossier |
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| Tier | 1 |
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| Source title | 2Q Cache Management Algorithm |
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| Source URL | https://arpit.substack.com/p/2q-cache-management-algorithm |
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| Source publisher / author | Arpit (Substack newsletter), explaining Johnson & Shasha's 1994 VLDB paper |
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| Source type | blog post (explainer of a primary paper) |
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| Source date (published) | Unknown — not stated |
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| Date researched | 2026-10-09 |
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| Researched by | tai (agent), model: Claude Sonnet 5, on behalf of retoor |
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| Research method | web search synthesis |
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| Confidence | High |
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| Status | Active |
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## Summary
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An accessible explainer of Johnson & Shasha's 1994 "2Q" buffer-replacement algorithm — a constant-overhead, no-tuning alternative to full LRU that influenced real database buffer-pool design, most notably PostgreSQL's.
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## Key findings
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- 2Q answers whether a constant-overhead-per-access scheme can match LRU/2 page-replacement performance; the 1994 paper's answer is yes, with no tuning required.
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- The design splits the buffer into three structures: a main LRU queue for confirmed-hot pages, a first-in (probationary) queue for newly-seen pages, and a ghost queue that stores only the identifiers of recently-evicted pages (not their data).
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- A page enters the probationary queue on first access; if it's re-referenced while still represented in the ghost queue, it gets promoted into the main queue.
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- This design is specifically scan-resistant: a one-time sequential scan fills and drains the probationary queue without ever polluting the main hot-page queue.
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- Per the source, 2Q's simplicity and effectiveness influenced PostgreSQL's own buffer-management design.
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## Pros / strengths
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- O(1), constant-overhead-per-access, no tuning parameters — directly addresses the "speed is important" constraint behind this entire research task, as a possible template if tai ever needs a real eviction policy rather than just tracking.
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- Real production lineage (PostgreSQL) gives confidence this isn't just an academic curiosity.
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## Cons / limitations / caveats
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- 2Q's own main-LRU-queue component is itself expensive to make concurrent under high contention — this is exactly the weakness that `arxiv-2511-21958-clock2q-plus.md` (Clock2Q+) sets out to fix by replacing that component with a CLOCK-style structure.
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- 2Q is an eviction-policy design for buffer pools; tai is not (yet) building eviction at all, only tracking — so 2Q is background context for a possible future phase, not something applicable today.
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## Relevance to tai
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Background/comparative context only for this research pass — explicitly not part of the current proposal (which is tracking-only, no eviction), but recorded here so a future eviction-policy decision doesn't have to rediscover 2Q as a candidate from scratch.
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## Changelog
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| Date | Change |
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| 2026-10-09 | Initial dossier created. |
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