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annotate doc/v2_planning/architecture_discussion.txt @ 1484:83d3c9ee6d65

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* changed MNIST dataset to use config.get_filepath_in_roots mechanism
author gdesjardins
date Tue, 05 Jul 2011 11:01:51 -0400
parents 93e1c7c9172b
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rev   line source
1260
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1 Arnaud:
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2
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3 From what I recall for the meeting last Friday, we saw three
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4 propositions for a runtime architecture for the experiments in
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5 pylearn.
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6
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7 The thing I noticed was that none of the three propositions was
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8 addressing the same problem. So not only do we have to choose which
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9 one(s) we want, but we also have to decide upon what do we need.
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10
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11 The proposals and the problems they address are outlined below, please
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12 comment if you see inaccuracies:
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13
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14 - PL's proposal, the hooks thing, was about enabling hooks to be
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15 registered at predefined points in functions and giving them access to
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16 the local variables. This addresses nicely the problem of collecting
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17 stats and printing progress.
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18
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19 - OB's proposal, the checkpoints thing, was about enabling the saving
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20 and loading of state at predefined points in the function. Other
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21 actions could also be performed at these points.
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22
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23 - JB's proposal, the new language thing, was about expressing
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24 algorithms with a control structure made of classes so that its state
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25 and structure could be preserved. It could also define new control
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26 structure to run things in parallel, over multiple machines or not.
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27
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28 Razvan:
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29
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30 I would add the following observations:
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31
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32 #1
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33 ---
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34
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35 This might be an artificial created issue, but I will write it down anyhow.
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36 We can decide later if we care about it.
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37
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38 Imagine you have some function provided by the library that implements
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39 some (complicated) pattern. Let say deeplearning ( the pretraining followed
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40 by finetuning). You instantiate this somehow :
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41
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42 instance = deeplearning(..)
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43
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44 Now you want to add some function to a given hook, checkpoint or whatever
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45 to calculate some statistics. You of course can do that ( the documentation
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46 can tell you how those hooks are named), but what the function will get is
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47 the locals defined in deeplearning. So you need to open up the file that
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48 implements that deeplearning and understand the code to figure out what
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49 variable does what.
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50
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51 Secondly if you need to execute a function in a unforseen place by the
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52 deeplearning,you can only do that by hacking the file implementing
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53 deeplearning function, i.e. by hacking the library. One can make sure that
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54 does not happen by overpopulating the code with hooks, but then we need
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55 a name for each hook.
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56
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57 I can add that probably in most cases the logic that goes into this is
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58 simple enough that the issues above are insignificant, but I might be wrong.
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59
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60
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61 #2
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62 ---
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63
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64 I think it is much healthier to think of James proposal as a glorified
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65 pipeline and not as a new language. You have components that you add in
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66 you pipeline. A CALL is such a component. You run the program by executing
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67 the pipeline ( which goes from one component to the other and calls it)
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68
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69 We are dealing with a glorified pipeline because :
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70 - when running the pipeline you can loop over a certain segment of the
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71 pipeline if you need to
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72 - you can, at run time, swtich between two possible terminations of the
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73 pipeline (the if command)
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74 - you can have two pipelines running in paralel, by running one
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75 component from one pipeline and then going to the other
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76
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77 You can also think of what James proposes as sort of the same as
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78 Olivier's with the following differences:
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79 - Olivier makes this entire mechanism invisible to the eye while in
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80 James' case it is explicit
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81 - James has inplicit checkpoints between any component, in Olivier's
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82 case you can define pipelines at different points ( maybe even more
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83 finely grained that what James mechanism offers)
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84 - One can imagine how, though Olivier did not exactly explained
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85 how you could have hooks in a template such that you do not actually need
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86 to hack that code.
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87
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88 James proposal also offers a way of expressing the distributed part in
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89 your main program. Is the same as having two pipelines between which you
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90 switch. Just think now each pipeline runs on a different machine
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91 independently and you just wait as the server for them to return. This
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92 is just one possibility.
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93
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94 In this proposal you can also see how you would solve the unforseen hooks
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95 problem, by having a special function that could alter the pipeline in some
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96 way (for example by introducing new components).
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97
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98 OD comments: It seemed to me that one major issue we are trying to solve with
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99 these approaches is that of being able to interrupt an experiment, then
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100 restart it later without starting again from scratch. OB and JB's proposals
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101 handle this more or less automatically (compared to PL's that would require
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102 more manual engineering of the save/load process). However it is not obvious
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103 to me that they would necessarily make things much easier, because:
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104 - One needs to use the same "framework" in all pieces of code (the +
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105 syntax for OB, or a single program for JB), otherwise some manual
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106 engineering will also be required. Can we reasonably expect the whole
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107 code to adhere to this? (maybe...)
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108 - If you want to be smart about what you (or rather do not) want to save,
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109 it may add yet another layer of complexity (I'm not sure though how hard
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110 it would be, so it'd be nice to have an example, e.g. if you are doing
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111 K-Fold CV with the training set stored in memory, but you don't want to
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112 save it on disk when serializing your experiment).