Skip to main content

PGA for Arbitrum chains

Priority Gas Auctions (PGA) is an optional transaction-ordering policy that you can enable on any Arbitrum chain. Under PGA, the Sequencer orders transactions by the priority fee attached to each one. During short ordering rounds that run several times per block, the Sequencer transfers the priority queue into the block it is building.

Activating PGA requires enabling tip collection on your chain. Once your chain collects tips, the Sequencer switches to PGA ordering automatically. PGA adds no operational overhead, which makes it viable for a much wider range of chains than Timeboost.

Your chain must collect priority fees, which ArbOS 61 supports. PGA orders transactions by tips.

As with all features on the Arbitrum stack, you can adopt PGA at your own discretion and on your own timeline.

To learn how PGA works, see the introduction to PGA.

Consider PGA for any chain with meaningful competition for block space. These chains are good candidates:

  • Chains with active DeFi, arbitrage, or liquidation activity. PGA converts latency competition into fee competition and routes the proceeds to your chain's fee collector.
  • Chains with latency-sensitive applications, such as proposer-based automated market makers (propAMMs). Per-transaction, just-in-time bidding suits workloads that need frequent priority-ordered inclusion.

Tradeoffs​

Costs​

Under first come first serve (FCFS) ordering, arrival time determines the order. Under PGA, willingness to pay determines it. Whenever your chain is congested, the Sequencer orders transactions that pay no priority fee behind those that do. The anti-starvation boost bounds how long they wait, but does not restore parity.

Revenue​

PGA revenue depends on MEV and competition for ordering. A chain with no congestion collects little in priority fees.

Enable PGA on your chain​

Prerequisites​

Before you start, confirm all four of the following:

  1. ArbOS 61 or newer. This release supports priority fee collection. PGA orders by tips, so it only activates once your chain collects them. To check what your chain runs and what the release contains, see ArbOS 61 Elara and the ArbOS software releases overview.

  2. Priority fee collection enabled. Collection requires all three of the following:

    • ArbOS 61 or newer
    • The chain's collect-tips flag set
    • The batch poster coinbase configured

    On Arbitrum One, you toggle collection with an ArbOwner precompile call to setCollectTips. For the call itself, the access-control rules, and a timing caveat that affects the enabling transaction, see priority fees collection. The ArbOwner precompile reference lists every method.

  3. Timeboost disabled. A configuration that enables both Timeboost and PGA behaves unpredictably. To find your current setting, see Timeboost for Arbitrum chains.

  4. A Nitro build that includes PGA. Confirm that the release you run supports it. The ArbOS software releases overview maps Nitro versions to ArbOS versions, and the Nitro support policy tells you which releases are supported.

Overview​

To enable PGA, complete two steps:

  1. Configure your Sequencer node's PGA rounds-per-block parameter.
  2. Enable priority fee collection on your chain, which activates PGA.

Step 1: Configure your Sequencer node for PGA​

Add the following to your Sequencer's node configuration file:

{
  "execution": {
    "sequencer": {
      "pga": {
        "rounds-per-block": 2
      },
      "timeboost": {
        "enable": false
      },
      "max-block-speed": "250ms"
    }
  }
}

rounds-per-block is the K parameter. With max-block-speed at 250ms and K=2, ordering rounds are 125ms long.

Step 2: Enable priority fee collection​

Caution

Complete Step 1 before you start Step 2. Enabling tip collection activates PGA immediately, with a default of one round per block.

Verify that your chain runs ArbOS 61 or newer. If your chain has a toggler contract for tip collection, use it. Otherwise, make an ArbOwner precompile call to setCollectTips.