TSAN Failure: DumpAndRead Test In TiFlash Nightly

by Alex Johnson 50 views

Bug Report

This document details a bug encountered during ThreadSanitizer (TSAN) testing of TiFlash, specifically within the UniversalPageStorageServiceCheckpointTest.DumpAndRead test case. The issue manifests as a Poco::FileNotFoundException, leading to test termination. This report outlines the steps to reproduce the bug, the expected behavior, the observed behavior, and the TiFlash version where the issue was identified.

Minimal Reproduce Step

The bug can be reproduced by executing TSAN tests within the TiFlash environment. This triggers the UniversalPageStorageServiceCheckpointTest.DumpAndRead test, which subsequently fails.

Expected Behavior

The expectation is that the UniversalPageStorageServiceCheckpointTest.DumpAndRead test should complete successfully without encountering any exceptions or errors when run under TSAN. The test should properly dump and read data, validating the functionality of the UniversalPageStorageService checkpoint mechanism.

Observed Behavior

Instead of a successful completion, the test terminates prematurely due to an uncaught exception of type Poco::FileNotFoundException. The error message indicates that the file required for the test is not found, leading to the termination of the test execution. The specific error message observed is: libc++abi: terminating due to uncaught exception of type Poco::FileNotFoundException: File not found.

TiFlash Version

The issue was observed in the nightly build of TiFlash with the commit hash e84ee46fa8a4842ea8d8ffbeb8e0.

Deep Dive into the Issue

The UniversalPageStorageServiceCheckpointTest.DumpAndRead test is designed to verify the checkpoint functionality of the UniversalPageStorageService in TiFlash. This service is crucial for ensuring data durability and consistency by periodically creating snapshots of the storage state. The DumpAndRead test specifically checks whether the service can correctly dump its current state to a file and subsequently read it back, restoring the state to its original condition. When TSAN is enabled, it introduces additional checks for data races and other threading-related issues, which can sometimes expose underlying problems that are not apparent during normal execution.

The failure observed, a Poco::FileNotFoundException, suggests that the test is unable to locate a necessary file during the dump or read process. This could be due to several reasons:

  1. Incorrect File Path: The test might be using an incorrect or outdated file path, leading to a failed lookup.
  2. Missing File: The required file might not be present in the expected location. This could be due to a build issue, a configuration error, or a problem with the test setup.
  3. Permissions Issue: The test process might not have the necessary permissions to access the file, resulting in a FileNotFoundException.
  4. Temporary File Issues: The test might be relying on temporary files that are being deleted or moved unexpectedly.
  5. TSAN Interference: While less likely, it's possible that TSAN is somehow interfering with the file system operations, causing the file to become inaccessible.

To further investigate this issue, the following steps should be taken:

  1. Verify File Paths: Double-check the file paths used in the test to ensure they are correct and up-to-date.
  2. Check File Existence: Ensure that the required file exists in the expected location. If it doesn't, investigate why it is missing.
  3. Examine Permissions: Verify that the test process has the necessary permissions to access the file. Adjust permissions if necessary.
  4. Review Temporary File Handling: If the test uses temporary files, review the code to ensure they are being handled correctly and are not being prematurely deleted.
  5. Disable TSAN (Temporarily): As a diagnostic step, temporarily disable TSAN and run the test to see if the issue persists. If the issue disappears, it suggests that TSAN might be exposing a threading-related problem that is indirectly causing the file to be inaccessible.

Potential Causes and Mitigation Strategies

The Poco::FileNotFoundException during the UniversalPageStorageServiceCheckpointTest.DumpAndRead test under TSAN points to a critical issue in TiFlash's file handling or test setup. The root cause could range from simple misconfigurations to more complex threading issues exposed by TSAN.

1. File Path Configuration

  • Problem: The test might be configured with an incorrect or outdated file path. This could happen if the test environment is not properly set up, or if the file paths are hardcoded and have changed over time.
  • Mitigation: Review the test code and configuration files to ensure that the file paths are correct and dynamically generated based on the environment. Use relative paths or environment variables to make the test more portable and less prone to errors caused by hardcoded paths.

2. Missing Dependency Files

  • Problem: The test might depend on certain files that are not present in the test environment. This could be due to incomplete build processes, missing data files, or incorrect deployment procedures.
  • Mitigation: Ensure that all necessary dependency files are included in the test environment. This can be achieved by properly packaging the test artifacts, using dependency management tools, and verifying the file integrity before running the test.

3. File Permissions

  • Problem: The test process might not have the necessary permissions to read or write the required files. This could be due to incorrect file ownership, restrictive access control lists, or security policies.
  • Mitigation: Adjust the file permissions to allow the test process to access the necessary files. This can be done by changing the file ownership, modifying the access control lists, or running the test with elevated privileges. However, be cautious when granting elevated privileges, as it can introduce security risks.

4. Race Conditions

  • Problem: TSAN is designed to detect race conditions, which can occur when multiple threads access the same file concurrently without proper synchronization. This can lead to file corruption, data loss, or unexpected exceptions.
  • Mitigation: Use appropriate synchronization mechanisms, such as mutexes or semaphores, to protect the file access operations. Ensure that all threads accessing the file are properly synchronized and that there are no data races. TSAN can help identify potential race conditions, but it's the developer's responsibility to fix them.

5. Temporary File Management

  • Problem: The test might be using temporary files that are not properly managed. This can lead to orphaned files, disk space exhaustion, or conflicts with other processes.
  • Mitigation: Use a robust temporary file management strategy. Create temporary files in a dedicated directory, ensure that they are properly deleted after use, and handle potential errors during file creation and deletion. Consider using libraries or utilities that provide temporary file management functionality.

6. TSAN Interference

  • Problem: In rare cases, TSAN itself might interfere with the file system operations, causing the test to fail. This could be due to bugs in TSAN or conflicts with other tools or libraries.
  • Mitigation: If you suspect that TSAN is interfering with the test, try disabling it temporarily to see if the issue persists. If the issue disappears, report the problem to the TSAN developers and provide them with a detailed description of the issue and the steps to reproduce it.

Conclusion

The UniversalPageStorageServiceCheckpointTest.DumpAndRead failure under TSAN in TiFlash nightly build e84ee46fa8a4842ea8d8ffbeb8e0 indicates a potential issue with file handling, test configuration, or threading synchronization. Thorough investigation is required to pinpoint the exact cause, and the mitigation strategies outlined above should be considered to address the problem. Resolving this issue is crucial to ensure the reliability and stability of TiFlash's data storage and checkpointing mechanisms.

For more information on ThreadSanitizer (TSAN) and its usage, refer to the official TSAN documentation. Remember to always validate your fixes and ensure that they do not introduce new issues. Testing is a continuous process, and a robust testing strategy is essential for maintaining high-quality software.