---

🧭 Table of Contents

• Introduction
• Quick Start
• Features
• Performance
• Usage
• Design
• Caveats
• License

---

✨ Introduction

Quill is a high-performance asynchronous logging library written in C++. It is designed for low-latency, performance-critical applications where every microsecond counts.

• Performance-Focused: Quill consistently outperforms many popular logging libraries.
• Feature-Rich: Packed with advanced features to meet diverse logging needs.
• Battle-Tested: Proven in demanding production environments. Extensively tested with sanitizers (ASan, UBSan, LSan) and fuzzed across a wide range of inputs.
• Extensive Documentation: Comprehensive guides and examples available.
• Community-Driven: Open to contributions, feedback, and feature requests.

Try it on Compiler Explorer

---

⏩ Quick Start

Getting started is easy and straightforward. Follow these steps to integrate the library into your project:

Installation

You can install Quill using the package manager of your choice:

Package Manager	Installation Command
vcpkg	vcpkg install quill
Conan	conan install quill
Homebrew	brew install quill
Meson WrapDB	meson wrap install quill
Conda	conda install -c conda-forge quill
Bzlmod	bazel_dep(name = "quill", version = "x.y.z")
xmake	xrepo install quill
nix	nix-shell -p quill-log
build2	libquill

Setup

Quickest Setup

For the quickest and simplest setup use simple_logger():

#include "quill/SimpleSetup.h"
#include "quill/LogFunctions.h"

int main()
{
  // log to the console
  auto* logger = quill::simple_logger();
  quill::info(logger, "Hello from {}!", "Quill");

  // log to a file
  auto* logger2 = quill::simple_logger("test.log");
  quill::warning(logger2, "This message goes to a file");
}

Detailed Setup

For more detailed control and configuration options, use the Backend and Frontend APIs:

#include "quill/Backend.h"
#include "quill/Frontend.h"
#include "quill/LogMacros.h"
#include "quill/Logger.h"
#include "quill/sinks/ConsoleSink.h"
#include <string_view>

int main()
{
  quill::Backend::start();

  quill::Logger* logger = quill::Frontend::create_or_get_logger(
    "root", quill::Frontend::create_or_get_sink<quill::ConsoleSink>("sink_id_1"));

  LOG_INFO(logger, "Hello from {}!", std::string_view{"Quill"});
}

Alternatively, you can use the macro-free mode. See here for details on performance trade-offs.

#include "quill/Backend.h"
#include "quill/Frontend.h"
#include "quill/LogFunctions.h"
#include "quill/Logger.h"
#include "quill/sinks/ConsoleSink.h"
#include <string_view>

int main()
{
  quill::Backend::start();

  quill::Logger* logger = quill::Frontend::create_or_get_logger(
    "root", quill::Frontend::create_or_get_sink<quill::ConsoleSink>("sink_id_1"));

  quill::info(logger, "Hello from {}!", std::string_view{"Quill"});
}

---

🎯 Features

• High-Performance: Ultra-low latency performance. View Benchmarks
• Asynchronous Processing: Background thread handles formatting and I/O, keeping your main thread responsive.
• Minimal Header Includes:
  • Frontend: Only Logger.h and LogMacros.h needed for logging. Lightweight with minimal dependencies.
  • Backend: Single .cpp file inclusion. No backend code injection into other translation units.
• Compile-Time Optimization: Eliminate specific log levels at compile time.
• Custom Formatters: Define your own log output patterns. See Formatters.
• Timestamp-Ordered Logs: Simplify debugging of multithreaded applications with chronologically ordered logs.
• Flexible Timestamps: Support for rdtsc, chrono, or custom clocks - ideal for simulations and more.
• Backtrace Logging: Store messages in a ring buffer for on-demand display. See Backtrace Logging
• Multiple Output Sinks: Console (with color), files (with rotation), JSON, ability to create custom sinks and more.
• Log Filtering: Process only relevant messages. See Filters.
• JSON Logging: Structured log output. See JSON Logging
• Configurable Queue Modes: bounded/unbounded and blocking/dropping options with monitoring on dropped messages, queue reallocations, and blocked hot threads.
• Crash Handling: Built-in signal handler for log preservation during crashes.
• Huge Pages Support (Linux): Leverage huge pages on the hot path for optimized performance.
• Wide Character Support (Windows): Compatible with ASCII-encoded wide strings and STL containers consisting of wide strings.
• Exception-Free Option: Configurable builds with or without exception handling.
• Clean Codebase: Maintained to high standards, warning-free even at strict levels.
• Type-Safe API: Built on {fmt} library.

---

🚀 Performance

System Configuration

• OS: Linux RHEL 9.4

• CPU: Intel Core i5-12600 (12th Gen) @ 4.8 GHz

• Compiler: GCC 13.1

• Benchmark-Tuned System: The system is specifically tuned for benchmarking.

• Command Line Parameters:

  $ cat /proc/cmdline
  BOOT_IMAGE=(hd0,gpt2)/vmlinuz-5.14.0-427.13.1.el9_4.x86_64 root=/dev/mapper/rhel-root ro crashkernel=1G-4G:192M,4G-64G:256M,64G-:512M resume=/dev/mapper/rhel-swap rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap rhgb quiet nohz=on nohz_full=1-5 rcu_nocbs=1-5 isolcpus=1-5 mitigations=off transparent_hugepage=never intel_pstate=disable nosoftlockup irqaffinity=0 processor.max_cstate=1 nosoftirqd sched_tick_offload=0 spec_store_bypass_disable=off spectre_v2=off iommu=pt
  

You can find the benchmark code on the logger_benchmarks repository.

Latency

The results presented in the tables below are measured in nanoseconds (ns).

The tables are sorted by the 95th percentile (lower is better).

Logging Numbers

LOG_INFO(logger, "Logging int: {}, int: {}, double: {}", i, j, d).

1 Thread Logging

Library	50th	75th	90th	95th	99th	99.9th
Quill Bounded Dropping Queue	8	8	9	9	10	12
Quill Unbounded Queue	8	8	9	9	11	13
fmtlog	8	9	9	10	12	13
PlatformLab NanoLog	13	14	16	18	21	24
MS BinLog	21	21	21	22	59	93
Quill Unbounded Queue (Log Functions)	27	28	29	30	31	33
XTR	7	7	29	31	33	55
Reckless	26	28	31	32	34	40
BqLog	42	42	43	75	83	94
Iyengar NanoLog	87	98	122	129	209	381
spdlog	145	148	151	154	162	171
g3log	775	781	787	791	805	967
Boost.Log	838	845	853	859	897	959

4 Threads Logging Simultaneously

Library	50th	75th	90th	95th	99th	99.9th
Quill Unbounded Queue	8	9	9	9	12	15
fmtlog	8	9	9	10	12	13
XTR	7	8	9	10	32	39
Quill Bounded Dropping Queue	8	9	10	11	13	15
PlatformLab NanoLog	9	13	15	17	22	26
MS BinLog	21	22	22	23	61	98
Reckless	19	23	26	27	31	57
Quill Unbounded Queue (Log Functions)	28	29	30	31	33	44
BqLog	47	49	50	122	143	4248
Iyengar NanoLog	58	90	124	132	178	1478
spdlog	214	260	327	359	452	754
Boost.Log	1640	2538	2793	2896	4150	4962
g3log	1336	4102	4501	4641	6079	7363

Logging Large Strings

Logging std::string over 35 characters to prevent the short string optimization.

LOG_INFO(logger, "Logging int: {}, int: {}, string: {}", i, j, large_string).

1 Thread Logging

Library	50th	75th	90th	95th	99th	99.9th
fmtlog	10	12	13	13	15	17
Quill Unbounded Queue	11	12	14	14	16	18
Quill Bounded Dropping Queue	12	13	14	15	16	19
MS BinLog	23	23	24	25	62	96
XTR	8	8	28	29	33	52
PlatformLab NanoLog	15	19	29	32	37	43
Quill Unbounded Queue (Log Functions)	31	33	34	35	36	38
BqLog	44	45	46	76	85	93
Reckless	89	105	111	114	120	131
Iyengar NanoLog	89	100	123	132	205	367
spdlog	129	133	137	141	149	157
g3log	565	568	571	573	582	740
Boost.Log	638	641	645	647	651	659

4 Threads Logging Simultaneously

Library	50th	75th	90th	95th	99th	99.9th
fmtlog	10	12	13	13	16	19
XTR	8	11	13	15	30	40
Quill Unbounded Queue	13	14	15	16	19	21
Quill Bounded Dropping Queue	13	15	16	17	20	22
PlatformLab NanoLog	11	16	20	24	38	46
MS BinLog	23	24	25	26	65	104
Quill Unbounded Queue (Log Functions)	31	33	35	36	39	46
Reckless	77	92	101	105	112	126
BqLog	51	55	59	119	136	2973
Iyengar NanoLog	55	86	103	128	170	1364
spdlog	196	227	281	310	395	690
Boost.Log	1357	2420	2607	2651	3939	5682
g3log	1050	3886	4271	4442	5693	6831

Logging Complex Types

Logging std::vector<std::string> containing 16 large strings, each ranging from 50 to 60 characters.

Note: some of the previous loggers do not support passing a std::vector as an argument.

LOG_INFO(logger, "Logging int: {}, int: {}, vector: {}", i, j, v).

1 Thread Logging

Library	50th	75th	90th	95th	99th	99.9th
Quill Bounded Dropping Queue	46	49	52	55	59	65
MS BinLog	67	69	71	73	79	279
Quill Unbounded Queue	139	150	160	165	173	183
XTR	286	297	341	346	353	589
fmtlog	646	660	685	705	733	767
spdlog	6301	6363	6419	6455	6802	7414
Boost.Log	34432	34623	34797	34928	35703	36233

4 Threads Logging Simultaneously

Library	50th	75th	90th	95th	99th	99.9th
Quill Bounded Dropping Queue	49	53	57	60	65	79
MS BinLog	69	72	74	76	82	292
Quill Unbounded Queue	84	91	98	103	113	130
fmtlog	675	701	740	756	779	809
XTR	627	1225	1317	1376	205300	287631
spdlog	6593	6671	6751	6815	7610	8794
Boost.Log	36322	80294	151775	177681	272649	362401

The benchmark methodology involves logging 20 messages in a loop, calculating and storing the average latency for those 20 messages, then waiting around ~2 milliseconds, and repeating this process for a specified number of iterations.

In the Quill Bounded Dropping benchmarks, the dropping queue size is set to 262,144 bytes, which is double the default size of 131,072 bytes.

Throughput

Throughput is measured by calculating the maximum number of log messages the backend logging thread can write to a log file per second (higher is better).

The tests were run on the same system used for the latency benchmarks.

Although Quill’s primary focus is not on maximizing throughput, it efficiently manages log messages across multiple threads. Benchmarking throughput of asynchronous logging libraries presents certain challenges. Some libraries may drop log messages, leading to smaller-than-expected log files, while others only provide asynchronous flushing, making it difficult to verify when the backend thread has fully processed all messages.

For comparison, we benchmark against other asynchronous logging libraries that offer guaranteed logging with a flush-and-wait mechanism.

Note that MS BinLog writes log data to a binary file, which requires offline formatting with an additional program—this makes it an unfair comparison, but it is included for reference.

Similarly, BqLog (binary log) uses the compressed binary log appender, and its log files are not human-readable unless processed offline. However, it is included for reference. The other version of BqLog is using a text appender and produces human-readable log files.

In the same way, Platformlab Nanolog also outputs binary logs and is expected to deliver high throughput. However, for reasons unexplained, the benchmark runs significantly slower (10x longer) than the other libraries, so it is excluded from the table.

Logging 4 million times the message "Iteration: {} int: {} double: {}"

Library	million msg/second	elapsed time
MS BinLog (binary log)	62.93	62 ms
BqLog (binary log)	14.71	271 ms
XTR	8.16	490 ms
Quill	5.24	763 ms
spdlog	4.32	925 ms
fmtlog	2.82	1417 ms
Reckless	2.72	1471 ms
Quill - Macro Free Mode	2.65	1510 ms
BqLog	2.60	1537 ms
Boost.Log	0.39	10102 ms

Compilation Time

Compile times are measured using clang 17 and for Release build.

Below, you can find the additional headers that the library will include when you need to log, following the recommended_usage example

There is also a compile-time benchmark measuring the compilation time of 2000 auto-generated log statements with various arguments. You can find it here. It takes approximately 30 seconds to compile.

Verdict

Quill excels in hot path latency benchmarks and supports high throughput, offering a rich set of features that outshines other logging libraries.

The human-readable log files facilitate easier debugging and analysis. While initially larger, they compress efficiently, with the size difference between human-readable and binary logs becoming minimal once zipped.

For example, for the same amount of messages:

ms_binlog_backend_total_time.blog (binary log): 177 MB
ms_binlog_backend_total_time.zip (zipped binary log): 35 MB

quill_backend_total_time.log (human-readable log): 448 MB
quill_backend_total_time.zip (zipped human-readable log): 47 MB

If Quill were not available, MS BinLog would be a strong alternative. It delivers great latency on the hot path and generates smaller binary log files. However, the binary logs necessitate offline processing with additional tools, which can be less convenient.

---

🧩 Usage

Also, see the Quick Start Guide for a brief introduction.

#include "quill/Backend.h"
#include "quill/Frontend.h"
#include "quill/LogMacros.h"
#include "quill/Logger.h"
#include "quill/sinks/ConsoleSink.h"
#include "quill/std/Array.h"

#include <string>
#include <utility>

int main()
{
  // Backend  
  quill::BackendOptions backend_options;
  quill::Backend::start(backend_options);

  // Frontend
  auto console_sink = quill::Frontend::create_or_get_sink<quill::ConsoleSink>("sink_id_1");
  quill::Logger* logger = quill::Frontend::create_or_get_logger("root", std::move(console_sink));

  // Change the LogLevel to print everything
  logger->set_log_level(quill::LogLevel::TraceL3);

  // A log message with number 123
  int a = 123;
  std::string l = "log";
  LOG_INFO(logger, "A {} message with number {}", l, a);

  // libfmt formatting language is supported 3.14e+00
  double pi = 3.141592653589793;
  LOG_INFO(logger, "libfmt formatting language is supported {:.2e}", pi);

  // Logging STD types is supported [1, 2, 3]
  std::array<int, 3> arr = {1, 2, 3};
  LOG_INFO(logger, "Logging STD types is supported {}", arr);

  // Logging STD types is supported [arr: [1, 2, 3]]
  LOGV_INFO(logger, "Logging STD types is supported", arr);

  // A message with two variables [a: 123, b: 3.17]
  double b = 3.17;
  LOGV_INFO(logger, "A message with two variables", a, b);

  for (uint32_t i = 0; i < 10; ++i)
  {
    // Will only log the message once per second
    LOG_INFO_LIMIT(std::chrono::seconds{1}, logger, "A {} message with number {}", l, a);
    LOGV_INFO_LIMIT(std::chrono::seconds{1}, logger, "A message with two variables", a, b);
  }

  LOG_TRACE_L3(logger, "Support for floats {:03.2f}", 1.23456);
  LOG_TRACE_L2(logger, "Positional arguments are {1} {0} ", "too", "supported");
  LOG_TRACE_L1(logger, "{:>30}", std::string_view {"right aligned"});
  LOG_DEBUG(logger, "Debugging foo {}", 1234);
  LOG_INFO(logger, "Welcome to Quill!");
  LOG_WARNING(logger, "A warning message.");
  LOG_ERROR(logger, "An error message. error code {}", 123);
  LOG_CRITICAL(logger, "A critical error.");
}

Output

External CMake

Building and Installing Quill

To get started with Quill, clone the repository and install it using CMake:

git clone https://github.com/odygrd/quill.git
cd quill
mkdir cmake_build
cd cmake_build
cmake ..
make install

• Custom Installation: Specify a custom directory with -DCMAKE_INSTALL_PREFIX=/path/to/install/dir.
• Build Examples: Include examples with -DQUILL_BUILD_EXAMPLES=ON.

Next, add Quill to your project using find_package():

find_package(quill REQUIRED)
target_link_libraries(your_target PUBLIC quill::quill)

Sample Directory Structure

Organize your project directory like this:

my_project/
├── CMakeLists.txt
├── main.cpp

Sample CMakeLists.txt

Here’s a sample CMakeLists.txt to get you started:

# If Quill is in a non-standard directory, specify its path.
set(CMAKE_PREFIX_PATH /path/to/quill)

# Find and link the Quill library.
find_package(quill REQUIRED)
add_executable(example main.cpp)
target_link_libraries(example PUBLIC quill::quill)

Embedded CMake

For a more integrated approach, embed Quill directly into your project:

Sample Directory Structure

my_project/
├── quill/            # Quill repo folder
├── CMakeLists.txt
├── main.cpp

Sample CMakeLists.txt

Use this CMakeLists.txt to include Quill directly:

cmake_minimum_required(VERSION 3.1.0)
project(my_project)

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

add_subdirectory(quill)
add_executable(my_project main.cpp)
target_link_libraries(my_project PUBLIC quill::quill)

Android NDK

When building Quill for Android, you might need to add this flag during configuration, but in most cases, it works without it:

-DQUILL_NO_THREAD_NAME_SUPPORT:BOOL=ON

For timestamps, use quill::ClockSourceType::System. Quill also includes an AndroidSink, which integrates with Android's logging system.

Minimal Example to Start Logging on Android

quill::Backend::start();

auto sink = quill::Frontend::create_or_get_sink<quill::AndroidSink>("app", [](){
    quill::AndroidSinkConfig asc;
    asc.set_tag("app");
    asc.set_format_message(true);
    return asc;
}());

auto logger = quill::Frontend::create_or_get_logger("root", std::move(sink),
                                                    quill::PatternFormatterOptions {}, 
                                                    quill::ClockSourceType::System);

LOG_INFO(logger, "Test {}", 123);

Meson

Using WrapDB

Easily integrate Quill with Meson’s wrapdb:

meson wrap install quill

Manual Integration

Copy the repository contents to your subprojects directory and add the following to your meson.build:

quill = subproject('quill')
quill_dep = quill.get_variable('quill_dep')
my_build_target = executable('name', 'main.cpp', dependencies : [quill_dep], install : true)

Bazel

Using Blzmod

Quill is available on BLZMOD for easy integration.

Manual Integration

For manual setup, add Quill to your BUILD.bazel file like this:

cc_binary(name = "app", srcs = ["main.cpp"], deps = ["//quill_path:quill"])

---

📐 Design

Frontend (caller-thread)

When invoking a LOG_ macro:

1. Creates a static constexpr metadata object to store Metadata such as the format string and source location.

2. Pushes the data SPSC lock-free queue. For each log message, the following variables are pushed

Variable	Description
timestamp	Current timestamp
Metadata*	Pointer to metadata information
Logger*	Pointer to the logger instance
DecodeFunc	A pointer to a templated function containing all the log message argument types, used for decoding the message
Args...	A serialized binary copy of each log message argument that was passed to the LOG_ macro

Backend

Consumes each message from the SPSC queue, retrieves all the necessary information and then formats the message. Subsequently, forwards the log message to all Sinks associated with the Logger.

---

🚨 Caveats

Quill may not work well with fork() since it spawns a background thread and fork() doesn't work well with multithreading.

If your application uses fork() and you want to log in the child processes as well, you should call quill::start() after the fork() call. Additionally, you should ensure that you write to different files in the parent and child processes to avoid conflicts.

For example :

#include "quill/Backend.h"
#include "quill/Frontend.h"
#include "quill/LogMacros.h"
#include "quill/Logger.h"
#include "quill/sinks/FileSink.h"

int main()
{
  // DO NOT CALL THIS BEFORE FORK
  // quill::Backend::start();

  if (fork() == 0)
  {
    quill::Backend::start();
        
    // Get or create a handler to the file - Write to a different file
    auto file_sink = quill::Frontend::create_or_get_sink<quill::FileSink>(
      "child.log");
    
    quill::Logger* logger = quill::Frontend::create_or_get_logger("root", std::move(file_sink));

    QUILL_LOG_INFO(logger, "Hello from Child {}", 123);
  }
  else
  {
    quill::Backend::start();
          
    // Get or create a handler to the file - Write to a different file
    auto file_sink = quill::Frontend::create_or_get_sink<quill::FileSink>(
      "parent.log");
    
    quill::Logger* logger = quill::Frontend::create_or_get_logger("root", std::move(file_sink));
    
    QUILL_LOG_INFO(logger, "Hello from Parent {}", 123);
  }
}

---

📝 License

Quill is licensed under the MIT License

Quill depends on third party libraries with separate copyright notices and license terms. Your use of the source code for these subcomponents is subject to the terms and conditions of the following licenses.

• (MIT License) {fmt}
• (MIT License) doctest