Block-header-only, faster startup client #7

1. 
   gavinandresen commented at 1:53 pm on December 20, 2010: contributor

   Bitcoin newbies have to endure an hour or two (or more) while bitcoin downloads and indexes all transactions and blocks.

   Satoshi has mostly implemented code that downloads just the block headers; as long as you’re not generating blocks, you don’t need all the old transactions.

2. 
   gavinandresen commented at 5:44 pm on December 20, 2010: contributor

   See the blockheaders feature branch here for initial work on this. Notes from Satoshi:

   CBlockIndex contains all the information of the block header, so to operate with headers only, I just maintain the CBlockIndex structure as usual. The nFile/nBlockPos are null, since the full block is not recorded on disk.

   The code to gracefully switch between client-mode on/off without deleting blk*.dat in between is not implemented yet. It would mostly be a matter of having non-client LoadBlockIndex ignore block index entries with null block pos. That would make it re-download those as full blocks. Switching back to client-mode is no problem, it doesn’t mind if the full blocks are there.

   If the initial block download becomes too long, we’ll want client mode as an option so new users can get running quickly. With graceful switch-off of client mode, they can later turn off client mode and have it download the full blocks if they want to start generating.

3. laanwj referenced this in commit 50d08dc1e1 on Sep 18, 2011
4. sipa referenced this in commit d73bad33e8 on Jun 2, 2013
5. 
   bardiharborow commented at 11:50 am on March 29, 2014: contributor

   @gavinandresen, we need to add another service category (NODE_SPV??) for SPV clients, so that they can operate without getting queried for blocks by other peers.
6. 
   laanwj commented at 11:54 am on March 29, 2014: member

   Why, how is this any different from what SPV clients do? See #3884 for another step towards this.
7. 
   bardiharborow commented at 0:24 am on March 30, 2014: contributor

   @laanwj, my understanding is that most SPV clients at the moment either get headers from a centralised source (Electrum) or use their own p2p network. I don’t know, some may use the main Bitcoin network, but wouldn’t they be queried for blocks by other clients and have to ignore those requests which could confuse the other peer (maybe?). I think it would be neater if other peers knew that you could be asked for headers, but not for blocks/txs. Anyway, sorry to bring up an old issue. Just thought someone should start working through the massive backlog, so I started from the back.
8. 
   christophebiocca commented at 0:29 am on March 30, 2014: none

   @bardiharborow SPV nodes talk to full nodes, not to each other (although that might be possible as well?). There’s a service bit specifically for offering full blocks instead of just headers: https://en.bitcoin.it/wiki/Protocol_specification#version
9. 
   sipa commented at 3:06 pm on March 30, 2014: member

   Electrum does SPV validation, but is in the strictly technical sense not an SPV node, as it does not participate in the P2P network.

   Actual SPV nodes (like Bitcoin Wallet for Android or Multibit) do connect to the P2P network (only to other full nodes, service flag NODE_NETWORK), and fetch blocks and headers from it. SPV nodes so far don’t connect to each other, both because they provide very little service (most don’t even keep all old headers around) and because they are only online sporadically.

10. 
    bardiharborow commented at 9:36 pm on March 30, 2014: contributor

    I’ve just realised that nodes can chose not to advertise their IP, which I assume is what they do. Does anyone know how hard this would be to implement? The only technical discussion seems to be 3 years old. Wouldn’t we also need a way of being alerted to transactions and downloading merkle branches? (This may already exist but the wiki maybe out of date and I’m not completely on top of the code.)
11. 
    sipa commented at 9:38 pm on March 30, 2014: member

    All this exists. SPV clients are used, and the protocol provides everything necessary. See BIP37 for example.

    The only thing we don’t have is the ability to run the reference code base in such an SPV client mode, where it doesn’t do full block validation. There are several steps towards that, but the first is certainly headers-first synchronization.

12. 
    laanwj commented at 2:18 am on March 31, 2014: member

    @bardiharborow This has all been done years ago. Please move questions like these to the stack exchange or forums, or #bitcoin on IRC. Github is not the place for basic discussion like this.
13. justmoon referenced this in commit 3de48d4a52 on Apr 7, 2014
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15. laanwj added the label P2P on May 9, 2014
16. kac- referenced this in commit 35f0a4e2e9 on Oct 8, 2014
17. 
    gavinandresen commented at 6:28 pm on October 28, 2014: contributor

    Headers-first download merged. And there are plenty of SPV wallets. Closing this.
18. gavinandresen closed this on Oct 28, 2014

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Contributors
gavinandresen bardiharborow laanwj christophebiocca sipa

Labels
Feature P2P