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Author Topic: How does the bitcoin client handle block distribution amongst connected peers?  (Read 1077 times)
zvs (OP)
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March 19, 2014, 02:49:32 PM
 #1

First set of data is irrelevant to question, just wanted to show dstat before the logfile output & stripping extraneous info

------sockets------ --net/eth0- -dsk/total- ---load-avg--- ----interrupts---
tot tcp udp raw frg| recv  send| read  writ| 1m   5m  15m |  51    52    53
986 810   3   0   0|  23k   17k|   0     0 |0.35 0.32 1.45|  92    74     0
986 810   3   0   0| 594k 7441k|   0   448k|0.32 0.31 1.44|1998  2183     0
986 810   3   0   0| 878k   54M|   0     0 |0.32 0.31 1.44|8278    11k    0
986 810   3   0   0|1062k   63M|   0     0 |0.32 0.31 1.44|9655    13k    0
986 810   3   0   0|1349k   72M|   0     0 |0.32 0.31 1.44|  11k   15k    0
986 810   3   0   0|1232k   50M|  24M    0 |0.32 0.31 1.44|9095    11k    0
986 810   3   0   0| 632k   23M|  44M   60k|0.38 0.32 1.44|4751  6215     0
986 810   3   0   0| 412k   19M|  44M    0 |0.38 0.32 1.44|3383  5325     0
986 810   3   0   0| 472k   17M|  19M    0 |0.38 0.32 1.44|4018  5333     0
986 810   3   0   0| 281k   16M|  16M    0 |0.38 0.32 1.44|2698  4440     0
986 810   3   0   0| 411k   18M|  20M    0 |0.38 0.32 1.44|3845  5218     0
986 810   3   0   0| 438k   18M|  18M    0 |0.35 0.32 1.43|3619  4957     0
986 810   3   0   0| 377k   17M|  12M   64k|0.35 0.32 1.43|3746  4934     0
986 810   3   0   0| 370k   16M|  12M   32k|0.35 0.32 1.43|3559  4908     0
986 810   3   0   0| 369k   18M|  16M    0 |0.35 0.32 1.43|3005  5266     0
986 810   3   0   0| 453k   17M|  13M    0 |0.35 0.32 1.43|3799  5294     0
986 810   3   0   0| 291k   16M|8688k    0 |0.32 0.31 1.43|2423  4368     0
986 810   3   0   0| 275k   15M|9200k    0 |0.32 0.31 1.43|2349  4285     0
986 810   3   0   0| 323k   15M|  15M    0 |0.32 0.31 1.43|2135  4029     0
986 810   3   0   0| 372k   15M|  10M    0 |0.32 0.31 1.43|3383  4571     0
986 810   3   0   0| 563k   12M|  10M    0 |0.32 0.31 1.43|3560  4088     0
986 810   3   0   0| 418k   15M|  14M   16k|0.37 0.32 1.42|3943  4697     0
986 810   3   0   0| 228k   13M|9852k    0 |0.37 0.32 1.42|2258  3587     0
986 810   3   0   0| 373k   15M|  11M    0 |0.37 0.32 1.42|3357  4305     0
986 810   3   0   0| 789k   14M|  11M    0 |0.37 0.32 1.42|2523  4063     0
986 810   3   0   0| 335k   13M|6556k    0 |0.37 0.32 1.42|2242  3832     0
986 810   3   0   0| 357k   14M|7280k    0 |0.34 0.32 1.42|3092  4362     0
986 810   3   0   0| 432k   12M|5376k 8192B|0.34 0.32 1.42|3945  4610     0


^^ This is from Philadelphia node, the other two had the blockchain in ramfs (this was the only node with any significant disk activity).

*****

OK, now this data is all from one block:

Germany (nogleg), an i7-4770 w/ 32 GB of RAM w/ blockchain in ramfs,

(tcp sockets open (maybe a handful or two aren't bitcoind connections), eth0 received, eth0 sent, timestamp (GMT))

629,656147,721483,06-03 04:11:28
629,528982,44778852,06-03 04:11:29
629,1026082,78608445,06-03 04:11:30
629,1108072,92873237,06-03 04:11:31
629,1057960,67983803,06-03 04:11:32
630,460841,28231563,06-03 04:11:33
630,163400,10998207,06-03 04:11:34
630,210372,8074017,06-03 04:11:35
630,126797,7413886,06-03 04:11:36


(capped at 88.57MB, or 93MB if we want to use fake infos, like manufacturers of hdds)

this is Philadelphia, PA, an e3-1270v1 w/ 16GB of RAM and SSD drive:

496,222221,244847,06-03 04:11:28
496,694519,6537351,06-03 04:11:29
496,867406,60435521,06-03 04:11:30
496,979387,67685208,06-03 04:11:31
496,820277,49585630,06-03 04:11:32
496,469354,19855676,06-03 04:11:33
496,126834,5740728,06-03 04:11:34
496,173320,4679675,06-03 04:11:35


This is Houston, TX, which is by far the fastest machine (quad opteron 6274, 64gb RAM -- ~1800c/m yam and nearly 300khash scrypt, hoho) -- blockchain in ramfs.  I don't want to use tmpfs since I'd rather have it crash & burn then start using swap space (so I have to remove disk space check every time since it doesn't work with ramfs.. well, I'd remove it regardless, since it's some small hit to efficiency)

I modified the source to allow 64 scriptcheck threads instead of 16, but unsure if it made any difference (it was "running" 64 threads at least).  the clock on this had a couple of seconds drift.  I took it offline after around 36 hours because of the inadequate upstream.  The rest were shut down at end of day GMT on march 8th.  I started Philadelphia & nogleg back up for approx. 23 hrs on march 12th (wanted to confirm correlating changes in tx propagation times on http://bitcoinstats.com/network/propagation)

Data for Houston, TX server:

530,183301,6583325,06-03 04:11:30
530,277817,12304357,06-03 04:11:31
530,271737,12301635,06-03 04:11:32
530,303381,12300903,06-03 04:11:33
530,298444,12300672,06-03 04:11:34
530,313658,12298154,06-03 04:11:35
529,320124,12292110,06-03 04:11:36
528,288593,12293872,06-03 04:11:37
528,263904,12300140,06-03 04:11:38
528,278275,12303968,06-03 04:11:39
526,281720,12291286,06-03 04:11:40
527,279488,12289710,06-03 04:11:41
527,287642,12291841,06-03 04:11:42
526,290481,12278198,06-03 04:11:43
527,192947,9499450,06-03 04:11:44
527,83951,3973766,06-03 04:11:45


Now my question is...  you can see this is on a 100mbps uplink and that it continued sending at that max speed for maybe 8 seconds or so after the other two had stopped.  I haven't looked through the code (& not even sure if I'd be able to tell if I did) or conducted a test, but would it be possible to delay someone receiving a block by deliberately decreasing your upstream bandwidth (or just by having poor upstream to begin with)?  i.e. I can receive and process any block very quickly, I then limit my upstream to, say, 3mbps.  that should make sure everyone that requests the block from me receives some small amt (~5kb/s).  does this mean they won't request the block from another source? 

I could see it requesting from 2 or 3 sources simultaneously, but more than that & you'd exacerbate the bandwidth issues.  Client should probably determine the best sources over time if it doesn't already.  I'm sure there's some relay in place between major pools (if not, there should be), but I'm guessing at least 1/4th of the blocks come from solo miners or small private pools...   problematic if someone can slow the transfer to a trickle w/o it breaking off request.

I used to think those Swiss nodes were doing that (I had them blocked, the vbitcoin eth zurich nodes, as they never sent data & just received), but maybe not...  or maybe they were, but since they weren't sending any data at all it requested the block from a secondary source semi-quickly?
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