andygrove opened a new issue, #7495: URL: https://github.com/apache/datafusion-comet/issues/7495
Part of #7267. ## Problem `ExplodeExec` copies every column that is not exploded once per array element, with `take` (`repeat_arrs_from_indices`, `native/operators/src/explode.rs:1291-1305`). It decides how many input rows to unnest at a time by output row count only (`next_chunk_rows`, `:320-342`), and it never splits one input row: a row whose array is longer than the batch size is built in one go and sliced afterwards. So the copied columns can pass 2 GiB even when the input is small. In `SELECT payload, explode(items) FROM t`, rows with a 300 KB `payload` and 900 elements each are unnested nine at a time, so each chunk is 8,100 output rows holding 2.4 GB of `payload`. One row with a 1 MiB payload and a 2,100-element array overflows on its own, at any batch size. The query fails with `Arrow error: Offset overflow error: 2147483648`. Spark's `GenerateExec` produces one row at a time and succeeds. The epic lists explode as honoring the batch size. It does for rows, but the copying makes each output row as large as its input row, so bytes per batch are not bounded. A unit test on the one-row case fails with `Offset overflow error: 2147483648` at `batch_size=8192` and at `batch_size=1024`. Line references are for main at 4e6b12290f. ## Workaround Lowering `spark.comet.batchSize` helps when many input rows share a chunk, but not for one row with a long array. `spark.comet.exec.explode.enabled=false` runs explode in Spark. ## Proposed fix - When picking the next chunk, also bound the predicted output bytes: for each copied variable-width column, sum the value length times the row's output length (`output_lens` already holds the second factor) over the chunk's rows. - Let one input row be split across several output batches, by taking ranges of its repeated indices instead of the whole row at once. ## Tests `take` computes the output size before it allocates, so the one-row case above fails in milliseconds today. After the fix, test the chunking with a small byte budget injected for the test, and check that one row with a long array comes out in several batches with the right values. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
