Implementation:ClickHouse ClickHouse Phdr Cache

Knowledge Sources	ClickHouse
Domains	Performance, System
Last Updated	2026-02-08 00:00 GMT

Overview

Caches ELF program headers to improve performance of dl_iterate_phdr calls.

Description

Intercepts dl_iterate_phdr and caches results to avoid repeated kernel calls. Significantly speeds up operations like stack unwinding in exception handling.

Usage

Use in performance-critical code that frequently calls dl_iterate_phdr, like exception handling or stack tracing.

Code Reference

Source Location

• Repository: ClickHouse
• File: base/base/phdr_cache.cpp
• Lines: 1-126

Signature

void updatePHDRCache();
bool hasPHDRCache();

// Intercepted function
extern "C" int dl_iterate_phdr(
    int (*callback)(dl_phdr_info * info, size_t size, void * data),
    void * data);

Import

// Automatically linked

Usage Examples

// Called once at startup
updatePHDRCache();

// All subsequent dl_iterate_phdr calls use cache
dl_iterate_phdr([](dl_phdr_info* info, size_t, void*) {
    // Fast cached iteration
    return 0;
}, nullptr);

Related Pages

• Principle:ClickHouse_ClickHouse_ELF_Program_Header_Caching