Hi All,

Here are some final results of testing with the reference implementation for compressing blocks and transactions. This implementation also concatenates blocks and transactions when possible so you'll see data sizes in the 1-2MB ranges.

Results below show the time it takes to sync the first part of the blockchain, comparing Zlib to the LZOx library.  (LZOf was also tried but wasn't found to be as good as LZOx).  The following shows tests run with and without latency.  With latency on the network, all compression libraries performed much better than without compression.

I don't think it's entirely obvious which is better, Zlib or LZO.  Although I prefer the higher compression of Zlib, overall I would have to give the edge to LZO.  With LZO we have the fastest most scalable option when at the lowest compression setting which will be a boost in performance for users that want peformance over compression, and then at the high end LZO provides decent compression which approaches Zlib, (although at a higher cost) but good for those that want to save more bandwidth.

Uncompressed 60ms Zlib-1 (60ms) Zlib-6 (60ms) LZOx-1 (60ms) LZOx-999 (60ms)
219 299 296 294 291
432 568 565 558 548
652 835 836 819 811
866 1106 1107 1081 1071
1082 1372 1381 1341 1333
1309 1644 1654 1605 1600
1535 1917 1936 1873 1875
1762 2191 2210 2141 2141
1992 2463 2486 2411 2411
2257 2748 2780 2694 2697
2627 3034 3076 2970 2983
3226 3416 3397 3266 3302
4010 3983 3773 3625 3703
4914 4503 4292 4127 4287
5806 4928 4719 4529 4821
6674 5249 5164 4840 5314
7563 5603 5669 5289 6002
8477 6054 6268 5858 6638
9843 7085 7278 6868 7679
11338 8215 8433 8044 8795


These results from testing on a highspeed wireless LAN (very small latency)

Results in seconds




Num blocks sync'd Uncompressed Zlib-1 Zlib-6 LZOx-1 LZOx-999
10000 255 232 233 231 257
20000 464 414 420 407 453
30000 677 594 611 585 650
40000 887 782 795 760 849
50000 1099 961 977 933 1048
60000 1310 1145 1167 1110 1259
70000 1512 1330 1362 1291 1470
80000 1714 1519 1552 1469 1679
90000 1917 1707 1747 1650 1882
100000 2122 1905 1950 1843 2111
110000 2333 2107 2151 2038 2329
120000 2560 2333 2376 2256 2580
130000 2835 2656 2679 2558 2921
140000 3274 3259 3161 3051 3466
150000 3662 3793 3547 3440 3919
160000 4040 4172 3937 3767 4416
170000 4425 4625 4379 4215 4958
180000 4860 5149 4895 4781 5560
190000 5855 6160 5898 5805 6557
200000 7004 7234 7051 6983 7770


The following show the compression ratio acheived for various sizes of data.  Zlib is the clear
winner for compressibility, with LZOx-999 coming close but at a cost.

range Zlib-1 cmp%
 Zlib-6 cmp% LZOx-1 cmp% LZOx-999 cmp%
0-250b 12.44 12.86 10.79 14.34
250-500b  19.33 12.97 10.34 11.11
600-700 16.72 n/a 12.91 17.25
700-800 6.37 7.65 4.83 8.07
900-1KB 6.54 6.95 5.64 7.9
1KB-10KB 25.08 25.65 21.21 22.65
10KB-100KB 19.77 21.57 14.37 19.02
100KB-200KB 21.49 23.56 15.37 21.55
200KB-300KB 23.66 24.18 16.91 22.76
300KB-400KB 23.4 23.7 16.5 21.38
400KB-500KB 24.6 24.85 17.56 22.43
500KB-600KB 25.51 26.55 18.51 23.4
600KB-700KB 27.25 28.41 19.91 25.46
700KB-800KB 27.58 29.18 20.26 27.17
800KB-900KB 27 29.11 20 27.4
900KB-1MB 28.19 29.38 21.15 26.43
1MB -2MB 27.41 29.46 21.33 27.73

The following shows the time in seconds to compress data of various sizes.  LZO1x is the
fastest and as file sizes increase, LZO1x time hardly increases at all.  It's interesing
to note as compression ratios increase LZOx-999 performs much worse than Zlib.  So LZO is faster
on the low end and slower (5 to 6 times slower) on the high end.

range Zlib-1 Zlib-6 LZOx-1 LZOx-999 cmp%
0-250b    0.001 0 0 0
250-500b   0 0 0 0.001
500-1KB     0 0 0 0.001
1KB-10KB    0.001 0.001 0 0.002
10KB-100KB   0.004 0.006 0.001 0.017
100KB-200KB  0.012 0.017 0.002 0.054
200KB-300KB  0.018 0.024 0.003 0.087
300KB-400KB  0.022 0.03 0.003 0.121
400KB-500KB  0.027 0.037 0.004 0.151
500KB-600KB  0.031 0.044 0.004 0.184
600KB-700KB  0.035 0.051 0.006 0.211
700KB-800KB  0.039 0.057 0.006 0.243
800KB-900KB  0.045 0.064 0.006 0.27
900KB-1MB   0.049 0.072 0.006 0.307

On 10/11/2015 8:46 AM, Jeff Garzik via bitcoin-dev wrote:
Comments:

1) cblock seems a reasonable way to extend the protocol.  Further wrapping should probably be done at the stream level.

2) zlib has crappy security track record.

3) A fallback path to non-compressed is required, should compression fail or crash.

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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