Solana Validator Control Stalls Transaction-Ordering Rule

SIMD-0649, a proposed Solana rule for inspecting transaction order, closed on Sept. 25 without merging. The draft would let validators reject a block when non-exempt transactions inside one entry batch violated fee-priority order. It would not decide which transactions enter the block, set batch boundaries or create a slot-wide priority queue.

Why it matters

Under the proposal, a leader could still select transactions, defer them to later batches and choose how those batches are formed. A higher-priority transaction in a later batch would not move ahead of a lower-priority transaction in an earlier batch. That makes the rule narrower than best execution and leaves meaningful discretion with block producers.

The proposed score is based on the leader's reward for including a transaction divided by its requested cost under the pre-execution cost model. It includes the priority fee and the unburned portion of the base fee, so it is not simply a ranking by the fee a user names. Equal-priority transactions could appear in either order, while simple vote transactions would be exempt.

Market impact

The draft would give traders and validators a testable way to check whether transactions placed in the same batch followed the specified order. To limit trivial batches, every batch except the final one would need to span at least two FEC sets, or 64 data shreds under the fixed-size rule. The final batch would remain exempt from the size minimum.

That safeguard would not eliminate every avenue for preferential treatment. Reviewers questioned whether leaders could close batches strategically, while the proposal also allows leaders to favor their own transactions through priority fees. The draft further raises latency questions for partially received data, but no measured batch distribution or delay estimate establishes how much the rule would change execution on mainnet. A revised proposal would need client support and evidence that meaningful competing transactions regularly share a batch.