Evaluation - SB Experiment mp3 to wav Migration and QA on Hadoop Cluster

Evaluator(s)

Bolette Jurik (SB)

Evaluation points

In this testbed experiment we focus on performance. The earlier experiment EVAL-LSDR6-1 on mp3 to wav migration and QA using xcorrSound also focused on correctness. Moving the workflow to Hadoop to prove scalability, should not affect correctness of the tool.

• Scalability The workflow must be able to process a large collection within reasonable time. That is we want to be able to migrate and QA a large collection of radio broadcast mp3-files (20 Tbytes - 175.000 files) within weeks rather than years. The goal of 1000 for Number Of Objects Per Hour (or 0.28 for number of objects per second) would mean that we can migrate the 20TB radio broadcast mp3 collection in a week.
• Reliability The workflow must run reliably without failing on a large number of files, and it must be possible to restart the workflow without loosing work.
• Correctness/Scalability We must believe to some extent that the automatic QA correctly identifies the "questionable" migrations, such that these can be checked in a manual QA process. We must however also insist that the number of migrations to check manually is minimal, as this is a very resource demanding process. The goal for QAFalseDifferentPercent has been changed to 2%. This means that we would have to check 3500 migrated 2 hour wav files manually. This is already too resource demanding. However the poor quality of the original files is a great challenge for the content comparison tool, and it turns out this is also too much to ask!

This table shows the results of the evaluation of the mp3 to wav migration and QA performed on the SB Hadoop Cluster.

Assessment of measurable points

*Based on the small experiment from April with max split size 128 below.

**Based on the large scale experiment from June below.

***This measure is not defined in the Metrics Catalogue, but we have kept it as a more readable extra supplement to number of objects per second.

Discussion and Conclusion

The conclusion is that the workflow does scale! We will not be able to migrate the collection in 1 week, but we will be able to do it in one month on the SB Hadoop cluster, which is considerably better than the one year needed without Hadoop (last evaluation).

The conclusion on correctness is really more of a discussion... The measure QAFalseDifferentPercent is defined as "Ratio of 'QA decided different'/'human judged same', that is ratio of content comparisons resulting in original and migrated different, even though human evaluation define original and migrated similar". As the large scale evaluations were performed on .5TB input, comprising 4998 2-hour mp3 files or 416.5 days, that is over a year of audio, we did not annotate the input, which means that ~8.7% is the number of files, where our audio content comparison tool reported that content of the original and the migrated files were not similar. Some of these may be actual migration errors. Most of them we however believe is due to the poor quality of the original material. Some of the original mp3 files have long periods of "nothing recorded" or silence. Silence or "almost silence" is very difficult to compare, and the tool will report not similar on these files. A better output would probably be "too much silence to perform content comparison". I would like to refer to the correctness evaluation of the xcorrSound waveform-compare tool done last year instead in section 2.4 Correctness based Benchmarks and Validation Tests of deliverable D11.2 Quality Assurance Workflow, Release 2 + Release Report.

Small Experiments April 2014

All run on a file list of 58 files (7.2Gb in total).

The small experiments were mainly run to decide an optimal max-split-size (or an optimal number of map-reduce map tasks). A split is a part of an input file that one map task is working on. Picking the appropriate size for the tasks for your job can radically change the performance of Hadoop. When working on text files, the default of letting the number of map tasks depend on the number of DFS blocks in the input files works well. We are not working on text files. The input to our map-reduce jobs are text files, but very small text files only containing lists of paths to the audio files, we actually want to work on. We thus want much smaller splits of only a few lines each. The max-split-size (mapred.max.split.size) is the maximum size of such a split in bytes.

The exact number of MR map tasks seem not to have a big influence on performance, as long as we have more than 2*12. That is as long as max split size is at most 256 on an input file list of 58 files. We note that we get approximately twice as many launched maps for the waveform-compare Hadoop job, simply because the input list is approximately twice as big, as it is a list of pairs. We can of course adjust this to get approximately the same number of jobs, but as the two first jobs FfmpegMigrate and Mpg321Convert run simultaneously, and the WaveformCompare job runs alone, we actually have approximately the same number of map tasks throughout the workflow.

The large scale experiments were held up for a while, due to too few connection to storage. Remember we are using the SB Hadoop Platform. As this job writes very much data, the Isilon disk I/O and CPU use were being maxed out, even though we were trying to "play nice" and only run 28 maps concurrently. The number of connections to the 16 nodes Isilon storage solution at SB were 2 when the small scale experiments were run. It was then set up to five connections before we ran the large scale experiments.

Large Scale Experiments June 2014

This line of tests will focus on scalability. If max-split-size=256 (bytes) gives us 2*12 maps on an input-txt-file with 58 files, this means 256 bytes is approx 58/12=4,8333 files, so one file is approx 256/4.8333=52.9655 bytes. Then if we want approx 2*12 maps on an input-txt-file with 1000 files, we want max-split-size to be approx 1000/12*52.9655 = 4413.7931 bytes.

The jobs were run on file-lists of approximately 1000 files (129GB); the max.split.size was set to 4414; and each job writes approximately 3.1TB of intermediate and output wav files (+ some small log files).

Assessment of non-measurable points

In the last evaluation, we did include ReliableAndStableAssessment Reliability - Runtime stability in the evaluation points, and we wrote true both in goal and in baseline value (Manual assessment: the experiment performed reliably and stably for 13 days, but then Taverna failed with  java.lang.OutOfMemoryError: Java heap space due to /tmp/ being filled up. All results were however saved, and the workflow could simply be restarted with a new starting point in the input list). This measure is not a part of the scape metrics catalogue, but stability judgement is and an evaluation follows here.

The experiment performed reliable and stably for around 4 hours. I will however note that this experiment was not focused on reliability, and all intermediate results are potentially lost if the workflow is killed. I will also note that we partitioned the input to the workflow, so it worked on only 1000 files at a time. This was done as the test environment had on upper limit on available storage, and the workflow produces approximately 3.1TB of output files for each 1000 input files. The workflow will fail if it does not have enough output storage. Working on only 1000 files at a time of course has the benefit, that only 1000 results can be lost at a time, and as the workflow seems to run stably for this size input it is reliable and stable in this configuration. Using this configuration however means that for a 20TB 175000 file collection, I need 175 input files and a script that starts the workflow 175 times sequentially (and roughly .5 Petabyte available storage).

A note about goals-objectives omitted, and why

This evaluation covers performance, reliability and functional suitability to some extent. We did not look at the metrics max object size handled in bytes and min object size handled in bytes. These measures would certainly contribute to the evaluation. Our collection (Danish Radio broadcasts, mp3) has mp3 files varying very little in size (approx. 2 hours, average file size 118Mb, largest file: 135Mb) and the workflow thus produces wav files varying very little in size (2 wav files of around 1.4Gb for one 118Mb mp3 file). The test mp3 files used under development were of course considerably smaller (around 7Mb) and produced smaller output (around 50Mb*2 per mp3 file). We think that the workflow can handle larger files as well, but this was not tested. We can report that for input min object size handled in bytes is around 7Mb (7000000 bytes) and max object size handled in bytes is around 135Mb (135000000 bytes). For output min object size handled in bytes is around 50Mb (50000000 bytes) and max object size handled in bytes is around 1.4Gb (1400000000 bytes). This would be an interesting measure to experiment further with.

We did also not look at the metrics throughput in bytes per second. This measure can be computed from number of objects per second or Number Of Objects Per Hour. The evaluation 2014 June 17th-23rd gave us Number Of Objects Per Hour=223. To compute throughput in bytes per second, we need the throughput size. Our question here is what throughput means. We wrote that the 1000 files in input were only approximately 129GB but they produced 3.1TB of intermediate and output wav files. Half of these (1.55TB) is output, and we will use this as the throughput size. Then for Number Of Objects Per Hour=223, we get 1.55/1000*223 = 0.34565TB or 0.34565×1024 = 353.9456Gb of throughput per hour, that is 353945600000 / 60 / 60 = 98318222 bytes or 98 MB of throughput per second.

The evaluation does not cover

• Organisational maturity
• Maintainability
• Planning and monitoring efficiency
• Commercial readiness

This experiment was focused on tools and platform and performance, and we will keep the evaluations to the specific experiment.

Technical details

The workflow that was used is version 4 of the Slim Migrate And QA mp3 to Wav Using Hadoop Jobs workflow available from http://www.myexperiment.org/workflows/4080.html

The Hadoop jobs that were used are from commit e1ec47d of the https://github.com/statsbiblioteket/scape-audio-qa-experiments project.

The waveform-compare tool that was used was from xcorrSound release v2.0.2 https://github.com/openplanets/scape-xcorrsound/releases/tag/v2.0.2.

The ffmpeg used was version 0.10 Copyright (c) 2000-2012 the FFmpeg developers built on Mar  9 2012 09:32:12 with gcc 4.4.6 20110731 (Red Hat 4.4.6-3).

The mpg321 used was version 0.2.10. Copyright (C) 2001, 2002 Joe Drew.

The cluster set up that was used was the June 2014 version of the SB Hadoop Platform.

WebDAV

The Taverna logs and outputs of the June experiment are stored on http://fue.onb.ac.at/scape-tb-evaluation/sb/LargeScaleAudioMigration/Mp3ToWavMigrationOnHadoop/ along with the SB scape Hadoop Cluster map-reduce client configuration.

Evaluation notes

• We have (stubbornly) kept the old measure Number Of Objects Per Hour in our evaluation, as it is simply easier to read when the processing time is as long as in this experiment.
• QAFalseDifferentPercent was introduced as a measure, when we were working on smaller annotated datasets. When we are working on large scale real life datasets it is problematic. A better idea would probably be to have a Dissimilar in Percent measure along with a Correctness judgement based on the Dissimilar in Percent measure along with prior correctness evaluations on annotated data. We would then also need a discussion of the adequacy of the solution when taken into acount the level of automation and the human resources still needed.

Conclusion

The conclusion is that we are able to migrate our 20TB mp3 collection to wav including quality assurance in one month on the SB Hadoop Platform. We however need roughly .5 Petabyte available storage, which is not feasible, and we will not do this migration. The xcorrSound waveform-compare tool has proven robust and easy to integrate in a larger workflow, and we will continue maintenance and maybe further development on xcorrSound.