fix(topk): avoid overflow panic in interleave emission for Utf8 - #20494
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aviralgarg05 wants to merge 7 commits into
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fix(topk): avoid overflow panic in interleave emission for Utf8#20494aviralgarg05 wants to merge 7 commits into
Utf8#20494aviralgarg05 wants to merge 7 commits into
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kosiew
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Mar 17, 2026
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@aviralgarg05
Thanks for working on this
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FYI, I encountered a similar case in sort merge: #20922, and there is a PR changing panic to error for interleavehttps://github.com/apache/arrow-rs/pull/9549 |
xudong963
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Mar 18, 2026
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run benchmarks |
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🤖 Benchmark completed (GKE) | trigger Details
Resource Usagetpch — base (merge-base)
tpch — branch
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🤖 Benchmark completed (GKE) | trigger Details
Resource Usagetpcds — base (merge-base)
tpcds — branch
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🤖 Benchmark completed (GKE) | trigger Details
Resource Usageclickbench_partitioned — base (merge-base)
clickbench_partitioned — branch
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alamb
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Mar 23, 2026
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Thank you for this contirbution @aviralgarg05 and @xudong963 -- I am a little worried about the complexity added in this patch for two reasons:
- It doesn't appear to be adequately tested
- It may introduce a performance regression when generating output
Typically when people hit offset errors related to using Utf8 (because of offset overflows) our advice is either:
- Use Utf8View ("String View")
- Use LargeUtf8
I am not sure it is a good tradeoff to slow down / make the Utf8 path more complex
Utf8
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Yes, the changes are in the hot path, for all cases, it'll do some checks. I encountered a similar overflow in the SPM path #20922, and introduced a different way to fix it: if we get the panic info, capture it, then progressively retry until no overflow, which only affects the overflow path. |
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Thank you for your contribution. Unfortunately, this pull request is stale because it has been open 60 days with no activity. Please remove the stale label or comment or this will be closed in 7 days. |
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Which issue does this PR close?
Rationale for this change
While testing, I found that
ORDER BY ... LIMITcould panic in TopK when interleaving very largeUtf8values. The problem was that TopK tried to interleave all selected rows in a single call, which can overflow Arrow’s i32 string offsets in extreme cases. This PR removes that panic path so the operator behaves safely under large-string workloads.What changes are included in this PR?
TopK.batch_sizefield.test_topk_heap_emit_with_state_respects_batch_size.Are these changes tested?
Yes.
datafusion/physical-plan/src/topk/mod.rsfor chunked TopK emission behavior.cargo fmt --all --check.cargo clippy -p datafusion-physical-plan --lib --tests -- -D warnings.cargo test -p datafusion-physical-plan topk::tests:: -- --nocapturethree times after final changes.Are there any user-facing changes?
Yes. For extreme large-string cases in
ORDER BY ... LIMIT, TopK no longer panics with overflow; it now follows normal error/execution handling.