What are the “Rejected Shares” in crypto mining?

Bitcoin mining pools are a way for Bitcoin miners to pool their resources together and share their hashing power while splitting the reward equally according to the amount of shares they contributed. Pooled mining effectively reduces the granularity of the block generation reward, smoothing it over time.

When you mine at a pool, you may often hear about “Accepted shares” and “Rejected Shares”.

A “share” is awarded to members of the Bitcoin mining pool who present a valid proof of work that their Bitcoin miner solved. Accepted shares mean your work is counting towards discovering new block, the more accepted shares you contribute, the more pool payout you’ll get.

Screenshot of mining platform: B.TOP

Rejected shares represent work that will not be applied toward a round in a mining pool. It occurs when you find a share and submit it to the mining pool after the pool has already moved on to the next block. In that case, you will have some “invalid shares” which don’t count in terms of revenue share, in other words, you’ll not get paid by the mining pool. This happens not too often thus it is considered normal. If everything is working correct, the percentage of rejected shares should be around 1%. A seasoned mining pool,such as BTC.TOP is capable of mantaining a Rejected Shares ratio less than 0.1%. As indicated on the above chart, the average rejected rate of the mining platform B.TOP (a susbidary of BTC.TOP) has been reduced to 0.03%.

Since that you only get paid for accepted shares, the desired goal is to minimize rejected shares and maximize accepted shares. Usually less than 2% rejected rate is considered normal, but if you detect a rate higher than 2%, or experience a sudden spike, most likely due to instability in the mining pool network.

Although rejected shares are inevitable, there is some way to reduce the rate, below are the best practices practiced by mainstream mining pools :

  • Using a correct and updated software, double check your algorithm, sometimes miners confuse the algorithms for different cryptos. For example, if you are mining LTC by using ETH algorithm, you’ll get tons of rejected shares;
  • Set your hardware configuration, if you’re using GPU mining, and your GPU core memory clocks very high or your power limit is too low, the hardware is having problem computing the correct hash;
  • Use reliable internet connection. If one specific mining machine shows a high rejected rate, try to replace internet cable, change router or switch interface, and keep an eye on the temperature of the machine for abnormalities. If you detect a high rejected rate in all the machines, try to check all the internet equipment such as broadband, routers or switches, in addition, check the internet condition of the mining facility. In China’s mining facilities, owners usually subscribe two telecom operators as part of contigency plan.

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