Bug #23510

Dataprep segfaults on long time windows

Added by David Adams 3 months ago. Updated about 1 month ago.

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I see segfault in dataprep when I try to process APA7 run 10157 which was taken with 100 ms (200k tick) time window.


#1 Updated by David Adams 3 months ago

In debugger, I see crash is in raw::Uncompress which is being called with a too-small output container. I don't know why we have to pre-size that vector but the decompression expects this.

That size is taken from digit.Samples() which returns unsigned short (max 65k) which is not sufficient for these long time windows. This is in dunetpc/dune/DataPrep/Tool/

I am modifying that tool to directly copy the compressed ADC vector (digit.ADCs()) in the case that the the compression is off (digit.Compression() == raw::kNone) and to otherwise log a warning message if the uncompressed size is smaller than the compressed size.

I assume we are not compressing RawDigit for protoDune or coldbox data. We should be careful not to compress MC data when the time window is too long. And, IMHO, RawDigit should be checking that no one asks for that.

#2 Updated by Thomas Junk 3 months ago

I am putting in a much-belated request to the LArSoft coordination meeting to enlarge fSamples to a ULong64_t. It broke a line or two of code in dunetpc (old 35-ton method), and perhaps other experiment code, so it needs to be rolled out carefully, but this is long overdue.

There is a fcl parameter for PDSPTPCRawDecoder_module that asks for the data to be re-compressed using the "Huffman" method in lardataobj/RawData/raw.cxx. program lacks this option as it was never used (except once by me last week when trying to decode one of these very long events).

The solution proposed above sounds safe, though one can imagine an overflowed Samples() still being larger than the compressed NADC and still being wrong. So far we only compress the MC raw digits, and MC doesn't have more than 16k ticks (that I know of).

#3 Updated by David Adams 3 months ago

I made the above change and verified I can now read long window data events directly from raw fragment data (where RawDigit is not compressed). Tom points out that we may want or have to compress the RawDigits if we write them in an intermediate step.

Change is committed to dunetpc.

#4 Updated by David Adams about 1 month ago

  • Status changed from Assigned to Closed

I suppose this is resolved.

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