[Bitcoin-development] Fwd: Re: Full Clients in the future - Blockchain management

Alan Reiner etotheipi at gmail.com
Sat Jun 2 17:15:26 UTC 2012


(response from Doug forwarded below)

It's a very good point.  I have no experience with database engines.  I 
had assumed that in most cases, data could always be indexed in RAM, and 
wanted to know where to go when that's not the case.  I will look into 
that solution, further.

I am very interested to solve the blockchain compression problem, and 
think I've got a great way that will not just compress the blockchain, 
but improve the network for lightweight clients.  But the idea is not 
fully formed yet, so I was holding off...



-------- Original Message --------
Subject: 	Re: [Bitcoin-development] Full Clients in the future - 
Blockchain management
Date: 	Sat, 2 Jun 2012 12:07:44 -0500
From: 	Douglas Huff <mith at jrbobdobbs.org>
To: 	Alan Reiner <etotheipi at gmail.com>



I think you're trying to solve something a little out of scope, really. 
Most of the issues aren't really issues for other clients using 
established storage mechanisms (bdb,SQLite,etc) and they're using them 
precisely because this is a problem that people have been working on for 
decades and a poor candidate for reinvention.

If you really look at what you're proposing it's fundamentally how bdb 
operates except your indexing format is usage domain specific and you're 
in charge of all the resource management semantics. While at the same 
time you'll be missing many of the newer features that make working 
with/recovering/diagnosing issues in the storage layer easier.

If you're really wanting to talk about pruning methods to prevent the 
massive amount of duplicated; but no longer pertinent, data that's a 
different story and please continue. :)

-- 
Douglas Huff

On Jun 2, 2012, at 10:40, Alan Reiner <etotheipi at gmail.com 
<mailto:etotheipi at gmail.com>> wrote:

> Devs,
>
> I have decided to upgrade Armory's blockchain utilities, partly out of 
> necessity due to a poor code decision I made before I even decided I 
> was making a client.  In an effort to avoid such mistakes again, I 
> want to do it "right" this time around, and realize that this is a 
> good discussion for all the devs that will have to deal with this 
> eventually...
>
> The part I'm having difficulty with, is the idea that in a few years 
> from now, it just may not be feasible to hold transactions 
> file-/pointers/ in RAM, because even that would overwhelm standard RAM 
> sizes.  Without any degree of blockchain compression, I see that the 
> most general, scalable solution is probably a complicated one.
>
> On the other hand, where this fails may be where we have already 
> predicted that the network will have to split into "super-nodes" and 
> "lite nodes."  In which case, this discussion is still a good one, but 
> just directed more towards the super-nodes.  But, there may still be a 
> point at which super-nodes don't have enough RAM to hold this data...
>
> (1)  As for how small you can get the data:  my original idea was that 
> the entire blockchain is stored on disk as blkXXXX.dat files.  I store 
> all transactions as 10-byte "file-references."  10 bytes would be
>
>     -- X in blkX.dat (2 bytes)
>     -- Tx start byte (4 bytes)
>     -- Tx size bytes (4 bytes)
>
> The file-refs would be stored in a multimap indexed by the first 6 
> bytes of the tx-hash.  In this way, when I search the multimap, I 
> potentially get a list of file-refs, and I might have to retrieve a 
> couple of tx from disk before finding the right one, but it would be a 
> good trade-off compared to storing all 32 bytes (that's assuming that 
> multimap nodes don't have too much overhead).
>
> But even with this, if there are 1,000,000,000 transactions in the 
> blockchain, each node is probably 48 bytes  (16 bytes + map/container 
> overhead), then you're talking about 48 GB to track all the data in 
> RAM.  mmap() may help here, but I'm not sure it's the right solution
>
> (2) What other ways are there, besides some kind of blockchain 
> compression, to maintain a multi-terabyte blockchain, assuming that 
> storing references to each tx would overwhelm available RAM?   Maybe 
> that assumption isn't necessary, but I think it prepares for the worst.
>
> Or maybe I'm too narrow in my focus.  How do other people envision 
> this will be handled in the future.  I've heard so many vague notions 
> of "well we could do /this/ or /that/, or it wouldn't be hard to do 
> /that/" but I haven't heard any serious proposals for it.  And while I 
> believe that blockchain compression will become ubiquitous in the 
> future, not everyone believes that, and there will undoubtedly be 
> users/devs that /want/ to maintain everything under all circumstances.
>
> -Alan
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