agreed.Comments:
1) cblock seems a reasonable way to extend the protocol. Further wrapping should probably be done at the stream level.
Zlib had a bad buffer overflow bug but that was in 2005 and it got a lot of press at the time. It's was fixed in version 1.2.3...we're on 1.2.8 now. I'm not aware of any other current issues with zlib. Do you have a citation?
2) zlib has crappy security track record.
agreed.3) A fallback path to non-compressed is required, should compression fail or crash.
I don't think LZO will give as good compression here but I will do some benchmarking when I can.
4) Most blocks and transactions have runs of zeroes and/or highly common bit-patterns, which contributes to useful compression even at smaller sizes. Peter Ts's most recent numbers bear this out. zlib has a dictionary (32K?) which works well with repeated patterns such as those you see with concatenated runs of transactions.
5) LZO should provide much better compression, at a cost of CPU performance and using a less-reviewed, less-field-tested library.
On Tue, Nov 10, 2015 at 11:30 AM, Tier Nolan via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:
On Tue, Nov 10, 2015 at 4:11 PM, Peter Tschipper <peter.tschipper@gmail.com> wrote:
There are better ways of sending new blocks, that's certainly true but for sending historical blocks and seding transactions I don't think so. This PR is really designed to save bandwidth and not intended to be a huge performance improvement in terms of time spent sending.
If the main point is for historical data, then sticking to just blocks is the best plan.
Since small blocks don't compress well, you could define a "cblocks" message that handles multiple blocks (just concatenate the block messages as payload before compression).
The sending peer could combine blocks so that each cblock is compressing at least 10kB of block data (or whatever is optimal). It is probably worth specifying a maximum size for network buffer reasons (either 1MB or 1 block maximum).
Similarly, transactions could be combined together and compressed "ctxs". The inv messages could be modified so that you can request groups of 10-20 transactions. That would depend on how much of an improvement compressed transactions would represent.
More generally, you could define a message which is a compressed message holder. That is probably to complex to be worth the effort though.
On Tue, Nov 10, 2015 at 5:40 AM, Johnathan Corgan via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:
On Mon, Nov 9, 2015 at 5:58 PM, gladoscc via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:
I think 25% bandwidth savings is certainly considerable, especially for people running full nodes in countries like Australia where internet bandwidth is lower and there are data caps.
This reinforces the idea that such trade-off decisions should be be local and negotiated between peers, not a required feature of the network P2P.--
Johnathan Corgan
Corgan Labs - SDR Training and Development Services
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