Quote from: pireff on November 09, 2019, 08:06:47 PM

Hello Bitcointalk members, as it's apparent from the title, i need a reliable way to detect orphan blocks. I wrote a custom explorer, and it's running quite fast actually, but i need an explanation on how exactly i can detect orphans, and mark them as so.

In normal circumstances, orphan occurs when block A and B are produced at the same time and that a portion of the network is building on Block A and the other is building on Block B. The miners will compete with each other until either of the sides find a block. This further extends the network and thus one of the forks now have a larger accumulated proof of work. The longer fork will supersede the shorter one. The problem with this is that nodes won't register (AFAIK) block B after they've received block A. Hence, you would need to have a very good connection to the network and a modified client to see all of the orphans that is on the network.

Quote from: pireff on November 09, 2019, 08:06:47 PM

What the longest chain fork due to orphan blocks is?

IIRC, the longest fork I've seen was during the 2013 hard fork and that lasted >30 blocks. Normally, the orphans should not go beyond 6 blocks.

Quote from: pireff on November 09, 2019, 08:06:47 PM

If on every block sync, i check the last 1000 blocks, is that enough to assume that every block beyond these 1000 is NOT an orphan?
Is the -1 confirmations the only way to detect them?

The orphan blocks are stored within the Bitcoin database. Parse the database and you should be able to sieve them out.