Batch processing of biophysical retirevals using multiple CPUs

Hi all,

I have a question related to batch processing in SNAP GUI via my ready-made XML graph. My intention is to retrieve biophysical parameters of atmospherically corrected Sentinel-2 image using Biophysical retrieval toolbox (S2 toolbox add-on in recent SNAP 4.0). When running the retrieval for single scene only, SNAP is able to use all CPUs (cores) specified in the configuration, however when running the batch processing of multiple scenes, only one CPU
(one core) is used. The retrieval itself takes quite a long time when using 20+ CPUs (about 5 hours?) and is takes literally ages on singe CPU…in fact I was unable to obtain a single result when only one CPU is used in batch mode. Do you have any suggestions, how to speed-up the batch processing of biophysical retrieval toolbox?


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Just one core is used? Sounds not good. I wonder if the cause for this is one of the operators you use or maybe the batch processing tool itself. Can you attach the graph here? This might help when investigating the issue.

Have you tried to do the batch processing on the command line? There is the gpt tool which you can use to execute a graph.

Dear Marco,

I use very simple Graph which:

  1. read the input L2A scene
  2. resample to 20 m resolution
  3. retrieve the biophysical parameters using Biophysical retrieval toolbox
  4. save the result

I also tried to skip the resampling part by resampling to 20 m externally, however the result is still the same - when executing the Biophysical retrieval toolbox via menu, the processing uses all my CPU cores, when using the Batch processing tool with graph, only one core is used. This is a major issue for Biophysical retrieval toolbox, since it takes many hours of processing, even with multi-core capability.

BTW: I recently updated to SNAP 5.0 and the spatial resampling in batch mode is not working any more - the tab with resampling setup requires to specify target resolution, but non of the options is correct. Do you have any comment on that?

Please find the Graph attached:

<graph id="Graph">
  <node id="Resample">
      <sourceProduct refid="Read"/>
    <parameters class="com.bc.ceres.binding.dom.XppDomElement">
  <node id="BiophysicalOp">
      <sourceProduct refid="Resample"/>
    <parameters class="com.bc.ceres.binding.dom.XppDomElement">
  <node id="Read">
    <parameters class="com.bc.ceres.binding.dom.XppDomElement">
  <node id="Write">
      <sourceProduct refid="BiophysicalOp"/>
    <parameters class="com.bc.ceres.binding.dom.XppDomElement">
  <applicationData id="Presentation">
    <node id="Resample">
      <displayPosition x="169.0" y="137.0"/>
    <node id="BiophysicalOp">
      <displayPosition x="280.0" y="138.0"/>
    <node id="Read">
      <displayPosition x="47.0" y="142.0"/>
    <node id="Write">
            <displayPosition x="419.0" y="139.0"/>

Best regards,

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I was able to reproduce the problem you have described.
It seems there is an issue when using operators in a graph which implement a certain method (computeTileStack()).
In this case the parallelisation isn’t working correct.
When using the operator directly, without a graph, the CPU usage is 100%. For me it dropped to 18% when used in a graph.
After specifying the -q option with a value of 120, I got the 100% again. It increases the number of allowed threads to 120.
Maybe you have to play a bit with this value. For me it is 10 * NumCores.
I haven’t tried a graph which contained both, the resample and the BiophysicalOp. It might happen that the resample op suffers from this setting or maybe you might need to set it even higher.

However, this is a bug we have to fix.

Thanks for the valuable report

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Dear Marco,

thank you for your quick reply. I was able to execute the batch processing of BiophysicalOP operator in command line GPT tool, the -q option really did the job and now the retrievals are running of all cores.

However, I’m still struggling with the Resample operator in GUI mode - it seems, that the GUI batch processing uses a new bullet switch (SNAP 5.0) instead of cells with values (SNAP 4.0) for setting the resampling parameters. For some reason, my preference in resampling all bands to 20 m resolution (i.e. Target resolution 20) is not working, since the GUI puts also the Target width and Target height 100 there. This produces an error message: if targetResolution is set, targetWidth, targetHeight, and referenceBandName must not be set . I was able to overcome this only by manually editing the XML file (i.e. deleting the targetWidth and targetHeight tags - see the previous XML graph attached) and executing the Graph via command line. Perhaps this is a bug in SNAP 5.0 related to new bullet switch option for resampling? Or am I doing something wrong?


I couldn’t reproduce this behaviour. The 100 pixels in width and height are replaced as soon as I have selected a product. Maybe this is the reason why you observer the problem. Maybe you need a product.

Hi all,

I have also a question about the biophysical operator. I have already tested the option with the .xml file (gpt operator.xml path_to_xml -q 160 -PInput=“path_to_xml” -POutput=“output.tif”), as well as the gpt command (gpt BiophysicalOp -PcomputeCab=true -PcomputeCw=true -PcomputeFapar=true -PcomputeFcover=true -PcomputeLAI=true -q 160 -Ssource=“path_to_resampled” -f GeoTIFF-BigTIFF -t output.tif) on a resampled product (extracted via another xml). Is there a performance difference between the two commands? Furthermore, I did not notice a time difference for the computation of 3 vs 5 indices. My main problem is that it takes too long even in 20+ cores machine. Which is the preferred method (command) in order to run the biophysical operators, and also are there any expected average times as benchmark (beacause I want to run for multiple products)?

Thank you,

You see probably no performance difference because the algorithms are not very complex and fast. That your processing is slow has probably other reasons.
Some thoughts for improving the processing:
You should not use the -q options, at least not setting it to such a high value. By default, the number of parallel threads is equal to the number of cores available. Which is a good choice usually.
When having 160 threads also the data is allocated for 160 tiles and tis might overload your memory.
Regarding memory. Probably you have also a lot available in your machine.
Change in the gpt.vmoptions the heap space settings to


or more. I would suggest 70%-80% of the available RAM.
You can also set the cache size used by gpt.
Use the -c option and set it to 70%-80% of the heap space.

Even though I used your recommended settings using -q 120, I still get heap space error.
I use it like that gpt “$wd/test20170615_glacier_velocity_commandline.xml” -q 120 -Pmaster="$wd/$master" -Pslave="$wd/$slave" -Poutput="$wd/$output.tif"
I also wonder why it didn’t happen last time when I processed the scene couple of days ago.
Please suggest.

What about the memory settings?
Have you changed it?

Not exactly. Could you please tell me how should I do it ?

Got it, sorry I missed your earlier comments. I do it and get back to you. Thanks

Hi there,

  • I changed the memory settings. I opened /snap/bin/gpt.vmoptions and uncomment the memory setting text. Now its Xmx16G.
  • Afterwards I run gpt “$wd/test20170615_glacier_velocity_commandline.xml” -q 120 -Pmaster="$wd/$master" -Pslave="$wd/$slave" -Poutput="$wd/$output.tif"
    Please see the snapshot what I got.

I look forward to your suggestion.

Probably 16G is not yet enough.
There might be three solutions.

  1. Change the parallelism from 120 to 60. I’m not sure if this will help.
  2. Change the tileSize. Have a look here : Using SNAP on Amazon Web Services
  3. Change the Cache size. After increasing the heap space you can also increase the cache size. It is also mentioned in the post above.

Now I have increased the heap space by Xmx28G (gpt.vmoptions).
I have also increased the cache size by changing

snap.jai.tileCacheSize = 24576
snap.jai.defaultTileSize = 512
I wonder snap.parallelism=1 is commented by # default. Is that alright ?

Anyway, after doing these settings, the graph processing is still going on (more than 2.30 hours). Couple of days ago, when the graph processing was normal, it took 1.15 hours. I wonder what really changed. Its the same processing graph, same dataset.
Does it have anything to do with snap/core/1689 ? See attachment.

Hi there,
I tried the settings, please see my above post. It is still not working. I even processed the graph using user interface, it also shows “Java heap scape” error. Please suggest. May be its a bug.

Yes, this is correct. If the value is not set, snap uses the number of cores available to set the parallelism.
Have you tried your graph with the Performance Tool (Tools -> Options -> Performance)? Have a look what it will suggest. The run might take a while.

The “Java heap scape” error indicates that 28G is still not enough.
Are you doing the Terrain-Correction for both products in one graph? If so, it might be better to split this into two graphs.

You can try to call gpt --diag This will show you the effective configuration.

Hi, when I click Tools, Options, Performance. It gives me

I am doing the Terrain Correction only once that too over velocity product.

Hi @marpet, somehow it is still not working. It’s a mystery for me now.
I have a strong feeling that it has something to do with allocated memory. Have a look here. snap/core/ size is full

Also when I call gpt --diag, it gives the configuration which seems pretty fine. what do you think?

please suggest. thanks.

The cache size of 0GB does not look so good.
Try adding ‘-c 18G’ to your run command.