Matt Corallo [ARCHIVE] on Nostr: 📅 Original date posted:2015-12-01 📝 Original message:I'm really not a fan of ...

📅 Original date posted:2015-12-01
📝 Original message: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. If there were a massive improvement, I'd find it acceptable, but the improvement you've shown really isn't all that much. 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. 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?).

All that said, I'd love a proposal that allows clients to download compressed blocks via an external daemon, especially during IBD. This could help people with very restrictive data caps do IBD instead of being pushed to revert to SPV. Additionally, I think we need more chain sync protocols so that the current P2P protocol isn't consensus-critical anymore.

On November 30, 2015 4:12:24 PM MST, Peter Tschipper via bitcoin-dev <bitcoin-dev at lists.linuxfoundation.org> wrote:
>
>@gmaxwell Bip Editor, and the Bitcoin Dev Community,
>
>After several weeks of experimenting and testing with various
>compression libraries I think there is enough evidence to show that
>compressing blocks and transactions is not only beneficial in reducing
>network bandwidth but is also provides a small performance boost when
>there is latency on the network.
>
>The following is a BIP Draft document for your review.
>(The alignment of the columns in the tables doesn't come out looking
>right in this email but if you cut and paste into a text document they
>are just fine)
>
>
><pre>
> BIP: ?
> Title: Datastream compression of Blocks and Tx's
> Author: Peter Tschipper <peter.tschipper at gmail.com>
> Status: Draft
> Type: Standards Track
> Created: 2015-11-30
></pre>
>
>==Abstract==
>
>To compress blocks and transactions, and to concatenate them together
>when possible, before sending.
>
>==Motivation==
>
>Bandwidth is an issue for users that run nodes in regions where
>bandwidth is expensive and subject to caps, in addition network latency
>in some regions can also be quite high. By compressing data we can
>reduce daily bandwidth used in a significant way while at the same time
>speed up the transmission of data throughout the network. This should
>encourage users to keep their nodes running longer and allow for more
>peer connections with less need for bandwidth throttling and in
>addition, may also encourage users in areas of marginal internet
>connectivity to run nodes where in the past they would not have been
>able to.
>
>==Specification==
>
>Advertise compression using a service bit. Both peers must have
>compression turned on in order for data to be compressed, sent, and
>decompressed.
>
>Blocks will be sent compressed.
>
>Transactions will be sent compressed with the exception of those less
>than 500 bytes.
>
>Blocks will be concatenated when possible.
>
>Transactions will be concatenated when possible or when a
>MSG_FILTERED_BLOCK is requested.
>
>Compression levels to be specified in "bitcoin.conf".
>
>Compression and decompression can be completely turned off.
>
>Although unlikely, if compression should fail then data will be sent
>uncompressed.
>
>The code for compressing and decompressing will be located in class
>CDataStream.
>
>Compression library LZO1x will be used.
>
>==Rationale==
>
>By using a service bit, compression and decompression can be turned
>on/off completely at both ends with a simple configuration setting. It
>is important to be able to easily turn off compression/decompression as
>a fall back mechanism. Using a service bit also makes the code fully
>compatible with any node that does not currently support compression. A
>node that do not present the correct service bit will simply receive
>data in standard uncompressed format.
>
>All blocks will be compressed. Even small blocks have been found to
>benefit from compression.
>
>Multiple block requests that are in queue will be concatenated together
>when possible to increase compressibility of smaller blocks.
>Concatenation will happen only if there are multiple block requests
>from
>the same remote peer. For example, if peer1 is requesting two blocks
>and they are both in queue then those two blocks will be concatenated.
>However, if peer1 is requesting 1 block and peer2 also one block, and
>they are both in queue, then each peer is sent only its block and no
>concatenation will occur. Up to 16 blocks (the max blocks in flight)
>can
>be concatenated but not exceeding the MAX_PROTOCOL_MESSAGE_LENGTH.
>Concatenated blocks compress better and further reduce bandwidth.
>
>Transactions below 500 bytes do not compress well and will be sent
>uncompressed unless they can be concatenated (see Table 3).
>
>Multiple transaction requests that are in queue will be concatenated
>when possible. This further reduces bandwidth needs and speeds the
>transfer of large requests for many transactions, such as with
>MSG_FILTERED_BLOCK requests, or when the system gets busy and is
>flooded
>with transactions. Concatenation happens in the same way as for
>blocks,
>described above.
>
>By allowing for differing compression levels which can be specified in
>the bitcoin.conf file, a node operator can tailor their compression to
>a
>level suitable for their system.
>
>Although unlikely, if compression fails for any reason then blocks and
>transactions will be sent uncompressed. Therefore, even with
>compression turned on, a node will be able to handle both compressed
>and
>uncompressed data from another peer.
>
>By Abstracting the compression/decompression code into class
>"CDataStream", compression can be easily applied to any datastream.
>
>The compression library LZO1x-1 does not compress to the extent that
>Zlib does but it is clearly the better performer (particularly as file
>sizes get larger), while at the same time providing very good
>compression (see Tables 1 and 2). Furthermore, LZO1x-999 can provide
>and almost Zlib like compression for those who wish to have more
>compression, although at a cost.
>
>==Test Results==
>
>With the LZO library, current test results show up to a 20% compression
>using LZO1x-1 and up to 27% when using LZO1x-999. In addition there is
>a marked performance improvement when there is latency on the network.
>From the test results, with a latency of 60ms there is an almost 30%
>improvement in performance when comparing LZO1x-1 compressed blocks
>with
>uncompressed blocks (see Table 5).
>
>The following table shows the percentage that blocks were compressed,
>using two different Zlib and LZO1x compression level settings.
>
>TABLE 1:
>range = data size range
>range Zlib-1 Zlib-6 LZO1x-1 LZO1x-999
>----------- ------ ------ ------- --------
>0-250 12.44 12.86 10.79 14.34
>250-500 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 4.37 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 table shows the time in seconds that a block of data
>takes
>to compress using different compression levels. One can clearly see
>that LZO1x-1 is the fastest and is not as affected when data sizes get
>larger.
>
>TABLE 2:
>range = data size range
>range Zlib-1 Zlib-6 LZO1x-1 LZO1x-999
>----------- ------ ------ ------- ---------
>0-250 0.001 0 0 0
>250-500 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
>
>TABLE 3:
>Compression of Transactions (without concatenation)
>range = block size range
>ubytes = average size of uncompressed transactions
>cbytes = average size of compressed transactions
>cmp% = the percentage amount that the transaction was compressed
>datapoints = number of datapoints taken
>
>range ubytes cbytes cmp% datapoints
>---------- ------ ------ ------ ----------
>0-250 220 227 -3.16 23780
>250-500 356 354 0.68 20882
>500-600 534 505 5.29 2772
>600-700 653 608 6.95 1853
>700-800 757 649 14.22 578
>800-900 822 758 7.77 661
>900-1KB 954 862 9.69 906
>1KB-10KB 2698 2222 17.64 3370
>10KB-100KB 15463 12092 21.80 15429
>
>The above table shows that transactions don't compress well below 500
>bytes but do very well beyond 1KB where there are a great deal of those
>large spam type transactions. However, most transactions happen to be
>in the < 500 byte range. So the next step was to appy concatenation
>for
>those smaller transactions. Doing that yielded some very good
>compression results. Some examples as follows:
>
>The best one that was seen was when 175 transactions were concatenated
>before being compressed. That yielded a 20% compression ratio, but
>that
>doesn't take into account the savings from the unneeded 174 message
>headers (24 bytes each) as well as 174 TCP ACKs of 52 bytes each which
>yields and additional 76*174 = 13224 byte savings, making for an
>overall
>bandwidth savings of 32%:
>
> 2015-11-18 01:09:09.002061 compressed data from 79890 to 67426
>txcount:175
>
>However, that was an extreme example. Most transaction aggregates were
>in the 2 to 10 transaction range. Such as the following:
>
>2015-11-17 21:08:28.469313 compressed data from 3199 to 2876 txcount:10
>
>But even here the savings of 10% was far better than the "nothing" we
>would get without concatenation, but add to that the 76 byte * 9
>transaction savings and we have a total 20% savings in bandwidth for
>transactions that otherwise would not be compressible. Therefore the
>concatenation of small transactions can also save bandwidth and speed
>up
>the transmission of those transactions through the network while
>keeping
>network and message queue chatter to a minimum.
>
>==Choice of Compression library==
>
>LZO was chosen over Zlib. LZO is the fastest most scalable option when
>used at the lowest compression setting which will be a performance
>boost
>for users that prefer performance over bandwidth savings. And at the
>higher end, LZO provides good compression (although at a higher cost)
>which approaches that of Zlib.
>
>Other compression libraries investigated were Snappy, LZOf, fastZlib
>and
>LZ4 however none of these were found to be suitable, either because
>they
>were not portable, lacked the flexibility to set compression levels or
>did not provide a useful compression ratio.
>
>The following two tables show results in seconds for syncing the first
>200,000 blocks. Tests were run on a high-speed wireless LAN with very
>little latency, and also run with a 60ms latency which was induced with
>"Netbalancer".
>
>TABLE 4:
>Results shown in seconds on highspeed wireless LAN (no induced latency)
>Num blks sync'd Uncmp Zlib-1 Zlib-6 LZO1x-1 LZO1x-999
>--------------- ----- ------ ------ ------- ---------
>10000 255 232 233 231 257
>20000 464 414 420 407 453
>30000 677 594 611 585 650
>40000 887 787 795 760 849
>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
>
>TABLE 5:
>Results shown in seconds with 60ms of induced latency
>Num blks sync'd Uncmp Zlib-1 Zlib-6 LZO1x-1 LZO1x-999
>--------------- ----- ------ ------ ------- ---------
>10000 219 299 296 294 291
>20000 432 568 565 558 548
>30000 652 835 836 819 811
>40000 866 1106 1107 1081 1071
>50000 1082 1372 1381 1341 1333
>60000 1309 1644 1654 1605 1600
>70000 1535 1917 1936 1873 1875
>80000 1762 2191 2210 2141 2141
>90000 1992 2463 2486 2411 2411
>100000 2257 2748 2780 2694 2697
>110000 2627 3034 3076 2970 2983
>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
>
>==Backward compatibility==
>
>Being unable to present the correct service bit, older clients will
>continue to receive standard uncompressed data and will be fully
>compatible with this change.
>
>==Fallback==
>
>It is important to be able to entirely and easily turn off compression
>and decompression as a fall back mechanism. This can be done with a
>simple bitcoin.conf setting of "compressionlevel=0". Only one of the
>two
>connected peers need to set compressionlevel=0 in order to turn off
>compression and decompression completely.
>
>==Deployment==
>
>This enhancement does not require a hard or soft fork.
>
>==Service Bit==
>
>During the testing of this implementation, service bit 28 was used,
>however this enhancement will require a permanently assigned service
>bit.
>
>==Implementation==
>
>This implementation depends on the LZO compression library: lzo-2.09
>
> https://github.com/ptschip/bitcoin/tree/compress
>
>==Copyright==
>
>This document is placed in the public domain.
>
>
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