papers/lp-208-dag-mempool/sections/06-composition.tex

\section{Composition With Sibling LPs}

\begin{table}[h]
\centering
\small
\begin{tabular}{@{}lp{9cm}@{}}
\toprule
\textbf{LP} & \textbf{Composition} \\
\midrule
LP-022 & ZAP wire protocol; the framing under schema IDs \texttt{0xF0}/\texttt{0xF1} \\
LP-077 & Round-digest binding; used by the consumer LP-209 ordering, not by DAG construction \\
LP-182 & Consensus wire / QuasarCert; the cert that finalizes the LP-209 ordering of this DAG \\
LP-200 & ZAP Stack umbrella; the immutable-buffer guarantee this LP relies on for content-addressing \\
LP-201 & ZAP P2P; schema IDs \texttt{0xF0}--\texttt{0xFF} do not collide with LP-201's \texttt{0xD0}--\texttt{0xDF} reservation; Kademlia DHT used for body storage \\
LP-202 & Pipelining contract; per-stage unwind primitives apply to the Select stage that consumes from this DAG \\
LP-203 & GPU-native verify; saturates the per-header sig-verify path \\
LP-205 & Pipelined Quasar (sibling); consumes from this DAG via the Select stage \\
LP-209 & Mysticeti ordering (sibling); the consumer that totally orders this DAG \\
LP-217 & Cert profile modes; the consumer's ordering is committed at the chosen mode \\
\bottomrule
\end{tabular}
\caption{Composition of LP-208 with sibling LPs.}
\label{tab:composition}
\end{table}

\subsection{With LP-205 (pipelined Quasar)}

The two LPs compose orthogonally:

\begin{itemize}[leftmargin=2em,nosep]
\item LP-205 specifies the per-leader pipeline at depth~$3$.
\item LP-208 specifies the per-validator emission of headers into a DAG.
\end{itemize}

A pipelined-Quasar chain using a DAG mempool runs:

\begin{enumerate}[leftmargin=2em,nosep]
\item Every validator emits DAGHeader every $K{=}$\SI{50}{\milli\second} (this LP).
\item LP-209 Mysticeti totally orders the DAG; the ordered output is the
  stream of txs.
\item The current leader's Select stage (LP-205) consumes from the
  Mysticeti output instead of a local mempool.
\item Build (LP-205) constructs a block frame referencing the consumed
  tx-set.
\item Sign (LP-205) produces a QuasarCert at the LP-217 mode.
\end{enumerate}

The leader's Select stage is the only LP-205 stage that changes; the
other two stages are unchanged. The aggregate throughput becomes
$\sum(\textrm{validator\_emit\_rate})$ rather than
$\min(\textrm{validator\_mempool\_rate})$.

\subsection{With LP-209 (Mysticeti ordering)}

The contract LP-208 makes to LP-209:

\begin{enumerate}[leftmargin=2em,nosep]
\item The DAG is content-addressed; LP-209 can refer to vertices by
  hash and rely on byte-identity across validators.
\item Headers from honest validators carry honest tx-hash lists and
  honest-best-effort parent pointers; LP-209 specifies how to recover
  ordering against adversarial headers.
\item Bodies are eventually consistent in the DHT under
  \texttt{body\_hash}; LP-209 specifies when to wait for body
  availability versus proceeding with header-only ordering.
\end{enumerate}

\subsection{With LP-203 (GPU verify)}

Tx sig verify runs on Blackwell as DAG headers arrive. Each header
carries up to $1000$ tx hashes; the bodies for those hashes are
batched into a single CUDA dispatch on the verify path. Verify
throughput tracks the LP-203 bench numbers directly -- at
$\sim$\SI{1}{\mega verifies/s} on Blackwell, the GPU is not the
bottleneck up to a per-validator emit rate of
$\sim$\SI{1}{\mega tx/s}.

\subsection{With LP-217 (cert profile modes)}

The DAG ordering (from LP-209 Mysticeti consuming this LP's DAG) is
committed at the LP-217 mode the consumer chain has configured --
PQ-fast for typical workloads, PQ-strict for custody/treasury,
PQ-heavy for archival anchoring. The DAG itself is mode-agnostic;
only the cert that finalizes the ordering of DAG vertices into
blocks carries the mode posture.

\section{Activation Marker}

\begin{verbatim}
activates:      2025-12-25T16:20:00-08:00
activates-unix: 1766708400
\end{verbatim}

DAG mempool is opt-in at activation. A chain enables it via genesis
config:

\begin{verbatim}
dag_mempool:
  enabled: true
  emission_ms: 50
  active_window_headers: 320
  schema_ids:
    header: 0xF0
    body: 0xF1
\end{verbatim}

\section{Backwards Compatibility}

None. Chains that do not enable DAG mempool use the single-mempool
model unchanged. LP-205 (pipelined Quasar) works against either
input source.

\section{Future Work}

\begin{itemize}[leftmargin=2em,nosep]
\item \textbf{LP-209} -- Mysticeti ordering: total-ordering of the
  DAG with sub-second finality; this LP's DAG is its input
  \cite{mysticeti2024}.
\item \textbf{LP-210} -- Block-STM speculation: speculative execute
  against the DAG's tx stream ahead of LP-209 ordering; commit on
  ordering arrival.
\item \textbf{LP-211} -- Cross-shard atomic commit: DAG mempools
  across peer shards exchange parent-pointers via cross-shard schema
  IDs (\texttt{0xF2}--\texttt{0xFF} reserved for this).
\end{itemize}