wgtmac commented on code in PR #45252:
URL: https://github.com/apache/arrow/pull/45252#discussion_r1914465079
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cpp/src/parquet/column_reader.cc:
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@@ -580,13 +580,20 @@ std::shared_ptr<Buffer>
SerializedPageReader::DecompressIfNeeded(
memcpy(decompressed, page_buffer->data(), levels_byte_len);
}
- // Decompress the values
- PARQUET_ASSIGN_OR_THROW(
- auto decompressed_len,
- decompressor_->Decompress(compressed_len - levels_byte_len,
- page_buffer->data() + levels_byte_len,
- uncompressed_len - levels_byte_len,
- decompression_buffer_->mutable_data() +
levels_byte_len));
+ // GH-31992: DataPageV2 may store only levels and no values
+ // when all values are null. In this case, we can avoid decompressing
+ // the rest of the page.
+ int64_t decompressed_len = 0;
+ if (uncompressed_len - levels_byte_len != 0) {
Review Comment:
LGTM. Let's add a simple test to cover this.
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