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How often do forks occur in the block chain? I'm interested in the small, one block forks that happen when two miners create a block at the similar time.

6

Blocks are orphaned once in a while, roughly every few hundred blocks:

http://blockchain.info/orphaned-blocks

There used to be a blockexplorer-provided list of chain reorganizations which can occur upon such events (might become available again someday):

http://blockexplorer.com/q/reorglog

These chain reorgs used to happen a few times per month.

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    "not very often" is a relative term, and doesn't mean a lot to me. It would be worth providing a ball-park figure on this question. – Highly Irregular Dec 8 '11 at 2:29
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    You can check that by using the link provided. They happened 3 to 9 times a month since July. – nponeccop Dec 8 '11 at 9:40
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    The reorglog is not very indicative of blockchain forks or orphaned nodes as a reorg only happens if a fork happens and the node was expecting the other branch to be the winner. Therefore most forks are not detected as the node already chooses the correct block on which the longest chain will be built. – cdecker Jan 3 '13 at 12:52
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    blockexplorer.com/q/reorglog gives a HTTP 404 error. Is there a new location where this information can be found? – Flow Apr 4 '13 at 16:17
  • @Flow: the whole site seems to be down. Dunno when/if it will be back soon. – Stéphane Gimenez Apr 4 '13 at 18:30
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I don't think the blockexplorer reorglog catches all blocks. http://blockchain.info/orphaned-blocks shows 1-2 detached blocks per day.

3

Update for everyone who stumbles up on this question. There is a paper that shows why it is hard to figure out the actual fork rate.

xxx

it's from this paper "Echoes of the Past: Recovering Blockchain Metrics From Merged Mining"

https://eprint.iacr.org/2018/1134.pdf

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    It's worth adding that increases in block propagation speed (esp in the last 2.5 years) have further suppressed the propagation of stale blocks. Blocks which are stale before the source ever announced them don't propagate, so speeding up the network causes you to see fewer of them and things like BIP152 and fibre have made the network a lot faster. – G. Maxwell Feb 5 at 22:50
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Both of the links in the previous two answers aren't working. Historic data (both, until March 2014) can be viewed on the internet archive. The last snapshot from blockexplorer.com: https://web.archive.org/web/20130313092352/http://blockexplorer.com/q/reorglog

The last snapshot from blockchain.info can be found in a similar way (stackexchange doesn't allow me to post more than 2 links, since I don't have enough reputation...).

An updated information, that unfortunately contain few details, is available in Organ Ofcorti's blog.
See, for example, http://organofcorti.blogspot.com/2014/05/may-11th-2014-weekly-hashrate.html , Table 2. The information is presented per week, in an image (not as text - which makes it a bit harder to analyze).

  • You can see in the chart above that more recent times (e.g. post height 403200, 2016-03) look a lot different than 2014, however. – G. Maxwell Feb 6 at 2:48

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