Power Save Mode and external file watcher indexing behavior in IntelliJ IDEA

Impact of Power Save Mode on File Watchers

Power Save Mode in IntelliJ IDEA does not completely kill the file system watcher, but it significantly alters how the IDE responds to external changes. While the IDE may still detect that a file has changed on disk, it suspends the automatic background indexing and real-time analysis that typically follow such an event.

Interaction with Indexing Settings

The "Suspend indexing when file is not modified for X minutes" setting is designed to prevent CPU spikes during massive external operations (like a git checkout or a build script). When Power Save Mode is active, it takes precedence over standard background indexing triggers. Consequently, the IDE will generally not initiate a full index update of externally modified files, regardless of the specific timeout settings, until the mode is disabled or a manual refresh is triggered.

Why UI Lag Still Occurs

If you experience UI lag while Power Save Mode is enabled, it is likely not caused by full project indexing, but by one of the following remaining active processes:

• File System Synchronization: The IDE still monitors the file system to ensure the editor reflects the current state of the disk (preventing data loss), even if it isn't indexing the symbols for code completion.
• External Dependency Updates: Certain JVM-level tasks or plugin-specific watchers may operate outside the standard "Power Save" scope.
• Memory Pressure: In very large projects, simply maintaining the project structure in memory can cause GC (Garbage Collection) pauses that manifest as UI lag, independent of indexing.

Verification Steps

To confirm how your specific project version is behaving, use this scoped test:

1. Enable File > Power Save Mode.
2. Modify a source file using an external editor (e.g., Notepad++ or Vim).
3. Return to IntelliJ. The file content should update in the editor, but notice that syntax highlighting or error markers for the new change do not appear.
4. Run File > Reload All from Disk. If the IDE suddenly triggers an indexing progress bar, it confirms that background indexing was indeed suspended.

Diagnostic Note: To provide a more precise answer regarding the lag, please specify if you are using a network-mapped drive (NFS/SMB) or a Docker-mounted volume, as these use different polling mechanisms than local SSDs.