Subject: Re: [bitcoin-dev] [BIP Draft] Datastream compression of Blocks and Transactions

From: Peter Tschipper <[email-masked]>
Date: Wed, 2 Dec 2015 15:05:10 -0800

On 30/11/2015 9:28 PM, Matt Corallo wrote:
> I'm really not a fan of this at all. To start with, adding a compression library that is directly accessible to the network on financial software is a really, really scary idea. 
Why scary?  LZO has no current security issues, and it will be
configureable by each node operator so it can be turned off completely
if needed or desired. 
> If there were a massive improvement, I'd find it acceptable, but the improvement you've shown really isn't all that much.
Why is 15% at the low end, to 27% at the high end not good?  It sounds
like a very good boost.   
>  The numbers you recently posted show it improving the very beginning of IBD somewhat over high-latency connections, but if we're throughput-limited after the very beginning of IBD, we should fix that, not compress the blocks. 
I only did the compression up to the 200,000 block to better isolate the
transmission of data from the post processing of blocks and determine
whether the compressing of data was adding to much to the total
transmission time.

I think it's clear from the data that as the data (blocks, transactions)
increase in size that (1) they compress better and (2) they have a
bigger and positive impact on improving performance when compressed.

> Additionally, I'd be very surprised if this had any significant effect on the speed at which new blocks traverse the network (do you have any simulations or other thoughts on this?).
>From the table below, at 120000 blocks the time to sync the chain was
roughly the same for compressed vs. uncompressed however after that
point as block sizes start increasing, all compression libraries
peformed much faster than uncompressed. The data provided in this
testing clearly shows that as block size increases, the performance
improvement by compressing data also increases.

TABLE 5:
Results shown in seconds with 60ms of induced latency
Num blks sync'd  Uncmp  Zlib-1  Zlib-6  LZO1x-1  LZO1x-999
---------------  -----  ------  ------  -------  ---------
120000           3226   3416    3397    3266     3302
130000           4010   3983    3773    3625     3703
140000           4914   4503    4292    4127     4287
150000           5806   4928    4719    4529     4821
160000           6674   5249    5164    4840     5314
170000           7563   5603    5669    5289     6002
180000           8477   6054    6268    5858     6638
190000           9843   7085    7278    6868     7679
200000           11338  8215    8433    8044     8795

As far as, what happens after the block is received, then obviously
compression isn't going to help in post processing and validating the
block, but in the pure transmission of the object it most certainly and
logically does and in a fairly direct proportion to the file size (a
file that is 20% smaller will be transmited "at least" 20% faster, you
can use any data transfer time calculator
<http://www.calctool.org/CALC/prof/computing/transfer_time> for that). 
The only issue, that I can see that required testing was to show how
much compression there would be, and how much time the compression of
the data would add to the sending of the data.