Clear DefinitionsStale Share
3 min read
Pronunciation
[steyl shair]
Analogy
Think of stale shares as completed homework assignments turned in after the teacher has already graded everyone else's work. The late assignment might be perfectly correct and represent real effort, but it no longer counts toward your grade because the class has moved on to the next topic. Similarly, a stale share represents real computational work by a miner that meets all the mathematical requirements, but arrives too late to be useful for the current mining target, resulting in wasted effort from the miner's perspective. Just as consistently turning in late assignments affects your overall grade, a high rate of stale shares reduces a miner's effective earning rate in a pool.
Definition
In cryptocurrency mining pools, a stale share is a valid proof-of-work solution submitted by a miner that arrives too late to be counted toward the current block being mined. Stale shares occur when another miner has already found a solution for the target block or when the mining pool has moved on to a new block, resulting in the late submission being rejected despite representing legitimate computational work.
Key Points Intro
Key Points
Network Latency: Delays in transmitting shares from the miner to the pool server, particularly affecting miners with poor internet connections or geographically distant from pool servers.
Workload Transitions: Occur when miners continue working on outdated block templates after the pool has moved to a new mining target due to another successful miner.
Reward Impact: Typically receive reduced or zero credit in pool reward calculations, directly impacting miner earnings despite representing legitimate work.
Performance Indicator: High stale share rates serve as diagnostic signals of connectivity issues, hardware problems, or inefficient mining software.
Example
A Bitcoin miner in Australia joins a mining pool with primary servers in Europe. The miner's hardware successfully computes a valid share with the appropriate difficulty and submits it to the pool. However, due to the approximately 300ms network latency between Australia and Europe, during that fraction of a second, another miner in the pool finds a full solution to the block, causing the pool to immediately switch to mining the next block. When the Australian miner's share arrives at the pool server, it's marked as stale because it was solving for a block target that's no longer relevant. The miner's dashboard shows a stale share rate of 2.8%, meaning almost 3% of their computational work yields no rewards. To reduce this rate, they reconfigure their setup to connect to the pool's Asia-Pacific servers instead of European ones, reducing network latency and bringing their stale share rate down to 0.7%, effectively increasing their rewards by over 2% without any change in hash rate.
Technical Deep Dive
Stale shares arise from the asynchronous nature of distributed mining operations and manifest differently across various pool architectures. At the protocol level, share staleness occurs when a miner works with an outdated mining context, typically containing either a previous block template or an outdated transaction mempool. Modern mining implementations use the stratum protocol, where mining jobs are identified by job IDs that help pools track which specific work assignment a submitted share corresponds to. Pools handle stale shares through different policies: some implement strict rejection (PROP and PPS systems typically give zero credit), while others use time-decay functions (certain PPLNS variations) where recent stales receive partial credit. The technical challenge for miners involves minimizing staleness through various optimizations: efficient work fetching algorithms that poll for new jobs at appropriate intervals without excessive network overhead, connection redundancy to multiple pool endpoints with automatic failover, and specialized networking configurations prioritizing mining traffic. Advanced mining operations implement statistical monitoring systems that track stale rates across different mining rigs, network paths, and pool connections to identify and address systemic issues. The relationship between hash rate, share submission frequency, and network latency creates complex optimization problems where higher hash rates require more aggressive new work fetching to prevent staleness during block transitions, while lower hash rates might optimize for reduced network traffic. Most professional mining operations consider stale rates below 1% acceptable, with rates above 3% indicating significant optimization opportunities.
Security Warning
Consistently high stale share rates may indicate network manipulation or man-in-the-middle attacks intercepting and delaying your submissions. If you observe sudden increases in stale rates without changing your hardware or internet connection, verify your pool connection settings and consider temporarily switching to a different pool to rule out targeted attacks.
Caveat
While minimizing stale shares is generally desirable, the appropriate optimization strategy depends on specific mining circumstances. Extremely aggressive polling for new work can sometimes increase stale rates by consuming bandwidth needed for share submission, particularly on limited connections. Additionally, some pools' reporting of stale shares may not perfectly align with their actual reward calculations, making optimization based solely on reported metrics potentially misleading. Geographic distribution of mining operations creates inherent advantages for miners located near major pool servers, contributing to centralization pressures despite the theoretically location-agnostic nature of proof-of-work. As mining difficulty increases and margins tighten, even small differences in stale rates can significantly impact profitability, making this formerly minor technical consideration increasingly important to mining economics.
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