Stale Share
A stale share is a valid proof of work submitted by a miner that arrives at the pool after the mining job it was based on has become outdated, typically because a new block has already been found on the network.
Understanding Stale Shares
Section titled “Understanding Stale Shares”When a new block is discovered on the Bitcoin network, all the work being done on the previous block template becomes irrelevant. The pool must quickly distribute a new job to all connected miners. However, there is always a small delay between the moment a new block is found and the moment every miner switches to the new job. Any shares submitted during this window are considered stale.
Imagine a newspaper printing press. If breaking news arrives after the paper has already started printing, those copies contain outdated headlines. Similarly, a stale share was valid work, but it was performed on data that is no longer relevant.
Stale shares are typically not rewarded by the pool because they cannot contribute to finding the next block. A high stale share rate is a problem for miners because it means wasted hashrate and lost revenue.
Practical Example
Section titled “Practical Example”A miner is working on block template #840,000. At 14:32:05, another pool finds block #840,000 and broadcasts it. At 14:32:05.3, the miner’s pool receives the new block and starts distributing a new job. At 14:32:05.5, the miner submits a share that was still based on the old block #840,000 template. This share is stale — it was valid work but is no longer useful. The miner begins receiving the new job at 14:32:05.6 and switches to working on block #840,001.