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I am running a private bitcoin network for which I changed the target time between two blocks to 12 seconds and the difficulty adjustment to 25 blocks interval. I ran the network for about 4 hours with 50 nodes. In one of the node's logs I observed that the blockchain height increased up to a maximum of 181 and then started decreasing, all the way to 38. what could be an explanation for such a strange behaviour.

Please refer to the log below:

2015-11-04 01:58:47 receive version message: /Satoshi:0.11.99/: version 70011, blocks=181, us=0.0.0.0:0, peer=2, peeraddr=127.0.0.1:44117
2015-11-04 01:58:47 UpdateTip: new best=0000005265ca4ce01ad0d06f45cf475bf303de3d64e942c5cf1177e00f346c78  height=180  log2_work=37.083283  tx=30941  date=2015-11-04 01:53:17 progress=1.000000  cache=0.0MiB(1tx)
2015-11-04 01:58:47 UpdateTip: new best=00000052a34cedf3c5ddbeb46d36644654523db855c4cce984d2623e840dd219  height=179  log2_work=37.082953  tx=30940  date=2015-11-04 01:53:10 progress=1.000000  cache=0.0MiB(2tx)
2015-11-04 01:58:47 UpdateTip: new best=00000030fd7652affb883f05fe0c98e7fe3fbc3cfd74808e061ed05ec61c22e6  height=178  log2_work=37.082623  tx=30939  date=2015-11-04 01:52:55 progress=1.000000  cache=0.0MiB(3tx)
2015-11-04 01:58:47 AddToWallet c32bcbd8102c602a5e71ee717232e204435f331dce6fbfb9eb5d552698faa95b
2015-11-04 01:58:47 AddToWallet 1c91517aeadd12bcbcfdf4a1423b671d405543ae9abfbd87078969ce1971663f
2015-11-04 01:58:47 AddToWallet b11f9c2e3b1ab3d3983da63783bb95903d89405243d0716ea88272a9261b7a33
bawejakunal
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2 Answers2

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Are all 50 nodes mining? What might happen is that some nodes are not in sync and keep mining on earlier blocks. If these soft forks are of a higher difficulty than the chain tip, the chain might rollback.

However it seems the logs are at the same second which might indicate that there is some race condition between receiving the blocks and printing the log messages.

Marius van der Wijden
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The log you provided shows you have two peers. If that's the only nodes(2+1) in the network then your chain is not gonna be stable without more fine tuning on the variables. My guess is that you changed some rules and a chain split&reorganization(soft fork) happened, the extra blocks become orphans after the reorganization.

Gary Chen
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