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Fix compression in ORC writer #12194

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merged 4 commits into from
Nov 21, 2022
Merged

Fix compression in ORC writer #12194

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ec8888c
fix selection of original vs compressed blocks, padding
vuule Nov 18, 2022
e29ea84
style
vuule Nov 18, 2022
c79c2d1
Merge branch 'branch-22.12' of https://github.com/rapidsai/cudf into …
vuule Nov 18, 2022
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vuule Nov 18, 2022
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7 changes: 4 additions & 3 deletions cpp/src/io/orc/stripe_enc.cu
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Original file line number Diff line number Diff line change
Expand Up @@ -1179,8 +1179,9 @@ __global__ void __launch_bounds__(256)
num_blocks = (ss.stream_size > 0) ? (ss.stream_size - 1) / comp_blk_size + 1 : 1;
for (uint32_t b = t; b < num_blocks; b += 256) {
uint32_t blk_size = min(comp_blk_size, ss.stream_size - min(b * comp_blk_size, ss.stream_size));
inputs[ss.first_block + b] = {src + b * comp_blk_size, blk_size};
auto const dst_offset = b * (padded_block_header_size + padded_comp_block_size);
inputs[ss.first_block + b] = {src + b * comp_blk_size, blk_size};
auto const dst_offset =
padded_block_header_size + b * (padded_block_header_size + padded_comp_block_size);
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Was this also wrongly computed before?

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Sort of. We insert a 3-byte header before each block when the compact the block in the output buffer. output buffer is actually same as compressed data buffer. So without the additional padded_block_header_size offset we would overwrite first three bytes of the first compressed block and then copy the block 3 bytes ahead, potentially doing even more damage to the block. This is why tests failed when @nvdbaranec fixed the SUCCESS condition locally. Luckily, this one change to the location where we write compressed block fixes all issues in compaction.

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The code that copies the blocks:

cudf/cpp/src/io/orc/stripe_enc.cu

Lines 1258 to 1264 in d335aa3

if (src != dst) {
for (uint32_t i = 0; i < blk_size; i += 1024) {
uint8_t v = (i + t < blk_size) ? src[i + t] : 0;
__syncthreads();
if (i + t < blk_size) { dst[i + t] = v; }
}
}

outputs[ss.first_block + b] = {dst + dst_offset, max_comp_blk_size};
results[ss.first_block + b] = {0, compression_status::FAILURE};
}
Expand Down Expand Up @@ -1234,7 +1235,7 @@ __global__ void __launch_bounds__(1024)
? results[ss.first_block + b].bytes_written
: src_len;
uint32_t blk_size24{};
if (results[ss.first_block + b].status == compression_status::SUCCESS) {
if (src_len < dst_len) {
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What are the semantics here? "If we failed to produce a compressed block smaller than the uncompressed data (either by failure or because of unlucky compression), just use the uncompressed data"?

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That's exactly right.
Planning to add a comment.

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We can also just invert the original condition, but this gives us additional benefits with uncompressable data.

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Right. This seems like a good way to do it.

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Wait, so there is no longer a check condition for SUCCESS compression?

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It is, indirectly, in the code slightly above it:

  auto dst_len = (results[ss.first_block + b].status == compression_status::SUCCESS)
                       ? results[ss.first_block + b].bytes_written
                       : src_len;

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We don't throw any exception if the decomp process failed?

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Added a comment. The logic should be refactored, but I don't want to make any unnecessary changes at this point.

// Copy from uncompressed source
src = inputs[ss.first_block + b].data();
results[ss.first_block + b].bytes_written = src_len;
Expand Down