in_tail: Add error log when flb fails to update the DB. Currently it fails silently.

[hardikkhurana]

Fixes #11416

Description:
When using the in_tail plugin with a database configured (db parameter), if the SQLite database becomes locked (e.g., receives SQLITE_BUSY or SQLITE_LOCKED), the plugin silently fails to update the file offset. The function flb_tail_db_file_offset returns -1, but no error message is logged to indicate that the persistence failed.

Change:
Add an error log line so that the error is not silent.

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Testing
Before we can approve your change; please submit the following in a comment:

• Example configuration file for the change

[SERVICE]
    Flush 1
    Log_Level info
[INPUT]
    Name tail
    Path /tmp/test.log
    DB   /tmp/tail.db
[OUTPUT]
    Name stdout

• Debug log output from testing the change

[error] [input:tail:tail.0] db: cannot update file offset for /tmp/test.log (id=1), ret=5

• [ N/A ] Attached Valgrind output that shows no leaks or memory corruption was found

If this is a change to packaging of containers or native binaries then please confirm it works for all targets.

• [N/A ] Run local packaging test showing all targets (including any new ones) build.
• [ N/A] Set ok-package-test label to test for all targets (requires maintainer to do).

Documentation

• [N/A ] Documentation required for this feature

Backporting

• [N/A] Backport to latest stable release.

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Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.

Summary by CodeRabbit

• Bug Fixes
  • Improved error logging and handling in the tail input plugin when updating tracked file offsets fails. This enhances diagnostic messages and operational visibility, making it easier to detect and troubleshoot file-tracking and offset-management issues during log collection, improving reliability of continuing or resuming log ingestion.

[coderabbitai]

📝 Walkthrough

Walkthrough

Adds an error log in flb_tail_db_file_offset when sqlite3_step fails to update a file offset in the SQLite DB; the code logs the filename, DB id and return code before performing existing cleanup and fallback logic.

Changes

Cohort / File(s)	Summary
Error Logging Enhancement plugins/in_tail/tail_db.c	Add an error log when sqlite3_step does not return SQLITE_DONE during file-offset update; existing cleanup/reset and re-insert-on-zero-changes logic unchanged.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Possibly related issues

• #11416: in_tail fails silently when SQLite DB is locked — This change adds the missing error log when offset updates fail, addressing the silent-failure symptom.
• in_tail: Data loss on exit/restart due to unhandled buffer (partial lines) #11265 — Related to file-offset update handling; added logging aids diagnosis.

Poem

🐰 I hopped through bytes and found a clue,

When offsets slipped and no one knew.
I call a warning, clear and bright,
So restarts don't replay the night.
🥕

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: adding an error log when flb fails to update the DB for the in_tail plugin.
Linked Issues check	✅ Passed	The PR implements the core requirement from issue #11416: adding an error log when flb_tail_db_file_offset fails to update the DB.
Out of Scope Changes check	✅ Passed	All changes are within scope: only a 3-line addition of error logging to the flb_tail_db_file_offset function.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[chatgpt-codex-connector]

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[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@plugins/in_tail/tail_db.c`:
- Around line 301-304: The flb_plg_error call in tail_db.c is broken by an
unterminated format string and misplaced quotes; fix the call in the error
branch where ctx->stmt_offset is handled by replacing the broken literal with a
single properly formatted format string and moving the variables into the
argument list (e.g. "db: cannot update file offset for %s (id=%" PRIu64 "),
ret=%d" , file->name, file->db_id, ret). Ensure the format uses the PRIu64 macro
concatenation exactly as above, remove the stray quote, and keep the subsequent
sqlite3_clear_bindings(ctx->stmt_offset) call unchanged.