Method createColumn

src/Storages/StorageFuzzQuery.cpp:24–102

}

ColumnPtr FuzzQuerySource::createColumn()
{
    auto column = ColumnString::create();
    ColumnString::Chars & data_to = column->getChars();
    ColumnString::Offsets & offsets_to = column->getOffsets();

    offsets_to.resize(block_size);
    IColumn::Offset offset = 0;

    auto fuzz_base = query;
    auto base_text = fuzz_base->formatForErrorMessage();
    size_t row_num = 0;

    /// Per-row attempt budget: when fuzzing keeps producing oversized variants we fall back
    /// to emitting the original (unfuzzed) query so the loop always makes progress. The
    /// formatted base query is guaranteed to fit `max_query_length` because
    /// `getConfiguration` rejects configurations where it does not.
    constexpr size_t max_attempts_per_row = 1024;

    while (row_num < block_size)
    {
        /// Stop generating rows promptly on cancellation (e.g. `KILL QUERY` or
        /// `max_execution_time`) instead of filling the rest of the block with fallback rows.
        if (isCancelled())
            break;

        String text_to_emit;
        bool produced = false;

        for (size_t attempt = 0; attempt < max_attempts_per_row; ++attempt)
        {
            ASTPtr new_query = fuzz_base->clone();

            auto base_before_fuzz = fuzz_base->formatForErrorMessage();
            fuzzer.fuzzMain(new_query);
            auto fuzzed_text = new_query->formatForErrorMessage();

            if (base_before_fuzz == fuzzed_text)
                continue;

            /// AST is too long, will start from the original query.
            if (fuzzed_text.size() > config.max_query_length)
            {
                fuzz_base = query;
                continue;
            }

            text_to_emit = std::move(fuzzed_text);
            fuzz_base = new_query;
            produced = true;
            break;
        }

        if (!produced)
        {
            /// Fallback: emit the formatted unfuzzed query. Always within `max_query_length`
            /// thanks to the upfront check in `getConfiguration`.
            text_to_emit = base_text;