> ## Documentation Index
> Fetch the complete documentation index at: https://docs.theblockchainlibrary.com/llms.txt
> Use this file to discover all available pages before exploring further.

# FIFO Transaction Ordering

> A transaction-ordering policy that processes eligible transactions in first-in, first-out order rather than primarily by fee bidding.

# FIFO Transaction Ordering

A transaction-ordering policy that processes eligible transactions in first-in, first-out order rather than primarily by fee bidding.

## Definition

A transaction-ordering policy that processes eligible transactions in first-in, first-out order rather than primarily by fee bidding.

## Why it matters

Transaction concepts explain how user actions are represented, ordered, executed, and confirmed on-chain.

## How it works

Validator nodes maintain a mempool where incoming transactions are timestamped or ordered by arrival sequence. When constructing a block, the validator selects transactions from the front of this queue until the block is full. No additional incentives can change the relative position of a transaction once it has been placed in the queue.

## Real-world example

Various research-focused blockchain projects implement FIFO ordering to mitigate the negative impacts of MEV on decentralized exchanges.

## Advantages

* Prevents front-running and MEV exploitation
* Promotes fairness and equal access
* Reduces complexity in transaction broadcasting

## Limitations

* Vulnerable to latency-based manipulation
* Hard to enforce in decentralized global networks
* May ignore urgency of time-sensitive transactions

## Common misconceptions

* Many think FIFO is inefficient, but it actually saves resources by eliminating complex fee-sorting algorithms.
* Users often confuse it with a lack of scalability, though it is purely about the sequencing of operations.

## Related knowledge

* [Blockchain](/categories/blockchain) — term
* [Cryptography](/categories/cryptography) — term
* [Web3](/categories/web3) — term

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**Canonical knowledge ID:** `glossary:fifo-transaction-ordering`