Function executeASTFuzzerQueries

src/Interpreters/executeQuery.cpp:2025–2184

static void executeASTFuzzerQueries(const ASTPtr & ast, const ContextMutablePtr & context, Float64 ast_fuzzer_runs_value, bool any_query)
{
    if (!any_query && !isReadOnlyQuery(ast))
        return;

    size_t num_runs = static_cast<size_t>(ast_fuzzer_runs_value);
    double fractional = ast_fuzzer_runs_value - static_cast<double>(num_runs);
    if (fractional > 0)
    {
        std::bernoulli_distribution dist(fractional);
        if (dist(thread_local_rng))
            ++num_runs;
    }

    if (num_runs == 0)
        return;

    auto logger = getLogger("ASTFuzzer");

    /// The fuzzer runs as a query finish callback, after the outer query's pipeline executor
    /// has stopped enforcing limits. Without these checks the outer query keeps spawning fuzzed
    /// queries while ignoring its own deadline, a KILL, or server shutdown, so it lingers in the
    /// processlist and can trip the stress test hung check.
    /// Some fuzzable queries (e.g. SHOW PROCESSLIST) are not inserted into the ProcessList, so
    /// the deadline/KILL check via checkTimeLimitSoft is unavailable; the shutdown metric still
    /// stops the loop in that case.
    QueryStatusPtr process_list_element = context->getProcessListElement();

    ASTPtr base_ast = ast;

    for (size_t i = 0; i < num_runs; ++i)
    {
        if (CurrentMetrics::get(CurrentMetrics::IsServerShuttingDown))
        {
            LOG_TRACE(logger, "Stopping AST fuzzer: the server is shutting down");
            break;
        }

        /// checkTimeLimitSoft returns false without throwing on a KILL or the outer deadline.
        if (process_list_element && !process_list_element->checkTimeLimitSoft())
        {
            LOG_TRACE(logger, "Stopping AST fuzzer: outer query was killed or timed out");
            break;
        }

        ASTPtr fuzzed_ast;
        NameToNameMap fuzzed_query_params;
        {
            auto [fuzzer, lock] = getGlobalASTFuzzer();
            fuzzed_ast = base_ast->clone();
            fuzzer->fuzzMain(fuzzed_ast);
            fuzzed_query_params = fuzzer->getLastQueryParameters();
        }

        /// Skip deeply nested ASTs to avoid stack overflow during formatting or execution.
        try
        {
            fuzzed_ast->checkDepth(500);