`repeat` on `LargeUtf8` aborts the process on a result size no allocation can satisfy

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@huong8373tt-beep 已经在做这个了。

开始于 2026年11月2日。

  • #26957 来自 @shahwazreza —— 未关闭
  • #27010 来自 @huong8373tt-beep —— 已关闭，未合并

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调研方向

从 datafusion/functions/src/string/repeat.rs 开始，将近 127-128 行处标量路径中的 LargeUtf8 上限与近 227-228 行处的数组路径进行比较。阅读 test_repeat_string_array_overflow 和复现代码片段，然后选择固定上限或 try_reserve 方案，使两个路径在计数为 1 << 60 时都返回错误。添加一个覆盖标量 LargeUtf8 和数组构建器的回归测试，并运行 repeat 相关测试。

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描述

bug good first issue

repeat on LargeUtf8 aborts the process on a result size no allocation can satisfy

Describe the bug

repeat caps the result at i32::MAX bytes for Utf8 and Utf8View, and returns an error above that. For LargeUtf8 the cap is i64::MAX, in both the scalar path and the array path. That cap admits sizes no allocation can satisfy. A result of 2^60 bytes (1 EiB) is larger than the virtual address space of x86_64 (48 or 57 bits) and aarch64 (at most 52 bits), so the allocator refuses it at once, whatever memory the machine has:

  • With both arguments scalar, s.repeat(count) cannot fail gracefully, so the refused allocation aborts the process: memory allocation of 1152921504606846976 bytes failed.
  • With an array of strings, the builder panics: failed to allocate memory for layout Layout { size: 1152921504606846976, align: 64 (1 << 6) }.

The existing test_repeat_string_array_overflow uses a count of i64::MAX, which the overflow check catches before any allocation.

To Reproduce

On main at 926901f90:

use std::sync::Arc;

use arrow::datatypes::Field;
use datafusion_common::ScalarValue;
use datafusion_common::config::ConfigOptions;
use datafusion_expr::{ColumnarValue, ReturnFieldArgs, ScalarFunctionArgs};
use datafusion_functions::string::repeat;

let udf = repeat();
let s = ScalarValue::LargeUtf8(Some("a".to_string()));
// With ScalarValue::Utf8: Err(Execution("string size overflow on repeat, max size is 2147483647, but got 1152921504606846976"))
let n = ScalarValue::Int64(Some(1 << 60));
let arg_fields = vec![
    Arc::new(Field::new("s", s.data_type(), true)),
    Arc::new(Field::new("n", n.data_type(), true)),
];
let return_field = udf
    .return_field_from_args(ReturnFieldArgs {
        arg_fields: &arg_fields,
        scalar_arguments: &[Some(&s), Some(&n)],
    })
    .unwrap();
let result = udf.invoke_with_args(ScalarFunctionArgs {
    args: vec![ColumnarValue::Scalar(s), ColumnarValue::Scalar(n)],
    arg_fields,
    number_rows: 1,
    return_field,
    config_options: Arc::new(ConfigOptions::default()),
});
// aborts: memory allocation of 1152921504606846976 bytes failed
Expected behavior

An error, as for Utf8, instead of an abort. Two fixes seem possible:

  • A fixed cap for LargeUtf8. PostgreSQL's repeat returns "requested length too large" above MaxAllocSize, 1 GB minus 1 (oracle_compat.c). DuckDB's strings are limited to u32::MAX bytes (MAX_STRING_SIZE).
  • Fallible allocation, such as try_reserve, so that a refused allocation becomes an error.

Which one should repeat use? Neither guards against an allocation that succeeds under overcommit and fails later when the pages are touched. Both turn this case, where the allocator refuses up front, into an error. #22688 tracks checked size accounting for string builders in general.

Additional context

Found by property-based tests that call each function with generated arguments, including large counts.

Willingness to contribute

I cannot contribute a fix for this bug at this time

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