nightly ftlog

An asynchronous logging library for high performance

7 releases

Uses new Rust 2021

new 0.2.4 Dec 9, 2022
0.2.3 Dec 8, 2022
0.2.1 Nov 25, 2022
0.1.1 Nov 1, 2022
0.1.0 Oct 30, 2022

#123 in Debugging

Download history 66/week @ 2022-10-27 24/week @ 2022-11-03 7/week @ 2022-11-10 37/week @ 2022-11-17 52/week @ 2022-11-24 51/week @ 2022-12-01

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Build Status License Latest Version ftlog

Logging is affected by the disk IO and pipe system call. Sequential log calls can be a bottleneck in scenarios where low latency is critical (e.g., high-frequency trading).

ftlog mitigates this bottleneck by sending messages to a dedicated logger thread and computing as little as possible in the main/worker thread.

ftlog can improve log performance in main/worker thread a few times over. See performance for details.

CAUTION: This crate uses the unchecked_math unstable feature and unsafe code. Use this crate only in rust nightly channel.


Add to your Cargo.toml:

ftlog = "0.2.0"

Configure and initialize ftlog at the start of your main function:

// ftlog re-export `log`'s macros, so no need to add `log` to dependencies
use ftlog::appender::FileAppender;
use ftlog::{debug, trace};
use log::{error, info, warn};

// minimal configuration with default setting

trace!("Hello world!");
debug!("Hello world!");
info!("Hello world!");
warn!("Hello world!");
error!("Hello world!");

// when main thread is done, logging thread may be busy printing messages
// wait for log output to flush, otherwise messages in memory yet might lost

A more complicated but feature rich usage:

use ftlog::{
    appender::{Duration, FileAppender, Period},
    FtLogFormatter, LevelFilter,

// configurate logger
let logger = ftlog::builder()
    // global max log level
    // global log formatter, timestamp is fixed for performance
    // use bounded channel to avoid large memory comsumption when overwhelmed with logs
    // Set `false` to tell ftlog to discard excessive logs.
    // Set `true` to block log call to wait for log thread.
    // here is the default settings
    .bounded(100_000, false) // .unbounded()
    // define root appender, pass anything that is Write and Send
    // omit `Builder::root` will write to stderr
    // level filter for root appender
    // write logs in ftlog::appender to "./ftlog-appender.log" instead of "./current.log"
    .filter("ftlog::appender", "ftlog-appender", LevelFilter::Error)
    .appender("ftlog-appender", FileAppender::new("ftlog-appender.log"))
    .expect("logger build failed");
// init global logger
logger.init().expect("set logger failed");

See ./examples for more (e.g. custom format).

Default Log Format

The datetime format is fixed for performance reasons.

2022-04-08 19:20:48.190+08 298ms INFO main [src/ftlog.rs:14] My log message

Here 298ms denotes the latency between the call of the log (e.g. log::info!("msg")) and the actual printing in log thread. Normally this is 0ms.

A large delay indicates that the log thread may be blocked by excessive log messages.

2022-04-10 21:27:15.996+08 0ms 2 INFO main [src/main.rs:29] limit running3 !

The number 2 above indicates how many log messages were discarded. Only shown if the frequency of logging for a single log call is limited (e.g. log::info!(limit=3000;"msg")).

Log with interval

ftlog allows to limit the write frequency for individual log calls.

If the above line is called multiple times within 3000ms, then it is logged only once, with an added number reflecting the number of discarded log messages.

Each log call ha an independent interval, so we can set different intervals for different log calls. Internally, ftlog records the last print time by a combination of (module name, file name, code line).


info!(limit=3000; "limit running {}s !", 3);

The minimal interval of the the specific log call above is 3000ms.

2022-04-10 21:27:10.996+08 0ms 0 INFO main [src/main.rs:29] limit running 3s !
2022-04-10 21:27:15.996+08 0ms 2 INFO main [src/main.rs:29] limit running 3s !

The number 2 above shows how many log messages is discarded since last log.

Log rotation

ftlog supports log rotation in local timezone. The available rotation periods are:

  • minute Period::Minute
  • hour Period::Hour
  • day Period::Day
  • month Period::Month
  • year Period::Year

Log rotation is configured in FileAppender, and the timestamp is appended to the end of the filename:

use ftlog::appender::{FileAppender, Period};

let logger = ftlog::builder()
    .root(FileAppender::rotate("./mylog.log", Period::Minute))

If the log file is configued to be split by minutes, the log file name has the format mylog-{MMMM}{YY}{DD}T{hh}{mm}.log. When divided by days, the log file name is something like mylog-{MMMM}{YY}{DD}.log.

Log filename examples:

$ ls
# by minute
# by hour
# by day
# by month
# by year
# omitting extension (e.g. "./log") will add datetime to the end of log filename

Clean outdated logs

With log rotation enabled, it is possible to clean outdated logs to free up disk space with FileAppender::rotate_with_expire method.

ftlog first finds files generated by ftlog and cleans outdated logs by last modified time. ftlog find generated logs by filename matched by file stem and added datetime.

ATTENTION: Any files that matchs the pattern will be deleted.

use ftlog::{appender::{Period, FileAppender, Duration}};

// clean files named like `current-\d{8}T\d{4}.log`.
// files like `another-\d{8}T\d{4}.log` or `current-\d{8}T\d{4}` will not be deleted, since the filenames' stem do not match.
// files like `current-\d{8}.log` will remains either, since the rotation durations do not match.

// Rotate every minute, clean stale logs that were modified 180s ago on each rotation
let appender = FileAppender::rotate_with_expire("./current.log", Period::Minute, Duration::seconds(180));
let logger = ftlog::builder()



message type Apple M1 Pro, 3.2GHz AMD EPYC 7T83, 3.2GHz
ftlog static string 89 ns/iter (±22) 197 ns/iter (±232)
ftlog with i32 123 ns/iter (±31) 263 ns/iter (±124)
output to file
static string 1,674 ns/iter (±123) 1,142 ns/iter (±56)
output to file
with i32 1,681 ns/iter (±59) 1,179 ns/iter (±46)
output to file with BufWriter
static string 279 ns/iter (±43) 550 ns/iter (±96)
output to file with BufWriter
with i32 278 ns/iter (±53) 565 ns/iter (±95)

License: MIT OR Apache-2.0


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