$$ \newcommand \PSfunction {\textbf{function }} \newcommand \PSreturn {\textbf{return }} \newcommand \PSendfunction {\textbf{end function}} \newcommand \PSswitch {\textbf{switch }} \newcommand \PScase {\textbf{case }} \newcommand \PSdefault {\textbf{default}} \newcommand \PSendswitch {\textbf{end switch}} \newcommand \PSfor {\textbf{for }} \newcommand \PSendfor {\textbf{end for}} \newcommand \PSwhile {\textbf{while }} \newcommand \PSendwhile {\textbf{end while}} \newcommand \PSdo {\textbf{ do}} \newcommand \PSif {\textbf{if }} \newcommand \PSelseif {\textbf{else if }} \newcommand \PSelse {\textbf{else}} \newcommand \PSthen {\textbf{ then}} \newcommand \PSendif {\textbf{end if}} \newcommand \PSnot {\textbf{not }} \newcommand \PScomment {\qquad \small \textsf} $$

$$ \newcommand \TP {\mathrm{TxPool}} \newcommand \FeePB {\mathrm{feePerByte}} \newcommand \FeeMul {\mathrm{feeThresholdMultiplier}} \newcommand \FeeExp {\mathrm{expFeeFactor}} \newcommand \PendingFB {\mathrm{pendingFullBlocks}} \newcommand \ComputeFeePerByte {\mathrm{ComputeFeePerByte}} $$

Prioritization

When the \( \TP \) becomes congested, a fee prioritization algorithm determines which transactions are enqueued into the pool and which are rejected.

The key parameter in this process is \( \FeePB \), which is calculated dynamically based on the number of pending blocks awaiting evaluation.

The \( \PendingFB \) is an unsigned integer that represents the number of uncommitted full blocks present in the \( \TP_{pq} \).

The function computeFeePerByte below demonstrates how this value is computed:

\( \textbf{Algorithm 2} \text{: Compute Fee per Byte} \)

$$ \begin{aligned} &\text{1: } \PSfunction \ComputeFeePerByte() \\ &\text{2: } \quad \FeePB \gets \FeeMul \\ &\text{3: } \quad \PSif \FeePB = 0 \land \TP.\PendingFB > 1 \PSthen \\ &\text{4: } \quad \quad \FeePB \gets 1 \\ &\text{5: } \quad \PSendif \\ &\text{6: } \quad \PSfor i {\textbf{ from }} 0 \textbf{ to } \TP.\PendingFB \PSdo \\ &\text{7: } \quad \quad \FeePB \gets \FeePB \cdot \TP.\FeeExp \\ &\text{8: } \quad \PSendfor \\ &\text{9: } \quad \PSreturn \FeePB \\ &\text{10: } \PSendfunction \end{aligned} $$

⚙️ IMPLEMENTATION

Compute fee per byte reference implementation.

The computeFeePerByte function begins by setting \( \FeePB \) equal to the \( \FeeMul \). When there is no congestion in \( \TP \), this value is \( 0 \).

However, if there are any full blocks currently pending in \( \TP_{pq} \), \( \FeePB \) is initially set to \( 1 \). This setup ensures that the subsequent multiplication step accumulates due to a non-zero base.

Next, for each of these full pending blocks, the \( \FeeExp \) is multiplied by the current \( \FeePB \) value—causing \( \FeePB \) to grow exponentially with the level of congestion.

The resulting \( \FeePB \) is then:

$$ \FeePB = \max\{1, \FeeMul \} \times \FeeExp^{\TP.\PendingFB} $$