DrainDotNet

DrainDotNet is a C# port and improvement of LogPai’s Drain log parser, with several improvements to make it faster, more reliable, and more user-friendly. It takes raw logs and automatically groups them into templates so you can easily see log patterns.

Key Improvements over the original Drain

• Core + Wrapper Split: The code is cleanly split into:
  • DrainCore → the pure clustering algorithm (tree, similarity, templates). No I/O.
  • LogParser → a wrapper that handles regex-based parsing, preprocessing, saving to CSV, and reloading later. This makes it easier to maintain and test the core logic separately.
• UniqueEventPatterns: You can provide regex patterns that mark certain tokens as important. If a log contains these tokens and they change, DrainDotNet will always create a new event/template instead of merging them. This gives you more control over clustering.
• Faster Parameter Extraction: The original Drain used regex-heavy logic for extracting parameters. DrainDotNet uses a simpler, token-based method that:
  • Runs much faster (no heavy regex overhead).
  • Handles tricky cases like time: 15> ms, which used to confuse Drain and produce broken templates like time: <*>>.
• Edge Case Handling: Robust against logs with odd punctuation or mixed tokens.
• Strongly Typed Output: Parse() returns a List<ParsedLog> in code (with LineId, Content, EventId, EventTemplate, ParameterList, and extra fields), so you don’t have to re-parse CSVs if you want to use results directly.
• Optional Auto-Save: Results are saved to CSV by default. You can disable this with autoSave: false if you only want in-memory results.
• Deterministic Reloading: Use ReloadResults() to rehydrate ParsedLog objects from CSV after an app restart.
• MD5 Hash Event IDs: Templates get stable 8-character Event IDs. Collisions are theoretically possible, but for typical datasets (even 100k+ templates) it’s practically safe.

How to use

1. Put your log file in the data folder (see Program.cs for path).

2. Build and run the project.

3. Results will be written into the outputDir path specified:

   • *_structured.csv — each log line matched with a template (includes ParameterList).
   • *_templates.csv — unique log templates with counts.

   Or use directly in code:

   using DrainDotNet; var logFormat = "<Date> <Time> <Pid> <Level> <Component> <Content>"; var parser = new LogParser(logFormat, indir: "./data/", outdir: "./result/"); // Parse logs and also save CSVs (default) var parsedLogs = parser.Parse("HDFS.log"); // Parse logs but keep results in memory only var parsedInMemory = parser.Parse("HDFS.log", autoSave: false); // Reload results later (if auto saved) from saved CSVs var reloaded = parser.ReloadResults("HDFS.log");

Using as a CLI Tool (new)

DrainDotNet is also available as a .NET global tool, so you can parse logs directly from the command line without writing code.

Install

dotnet tool install -g DrainDotNet.Tool

Usage

draindotnet parse --log <logFile> --format "<LogFormat>" [--indir <inputDir>] [--out <outputDir>]

Example (HDFS sample)

draindotnet parse --log HDFS_2k.log --format "<Date> <Time> <Pid> <Level> <Component>: <Content>" --indir ./SampleApp/data/loghub_2k/HDFS --out ./SampleApp/result

This will generate:

• HDFS_2k.log_structured.csv → structured logs with parameters
• HDFS_2k.log_templates.csv → unique log templates with counts

License

Apache 2.0 (same as the original Drain).