What is mdworker on Mac?

What mdworker does

mdworker_shared is Spotlight’s file reader. When a file is created or changes, the coordinator mds hands it to a worker, which loads the right importer for that file type (PDF, Word, image, source code, a third-party format) and pulls out text, titles, authors, dimensions and other metadata. The worker passes the results to mds_stores, which writes them into the index.

On current macOS the process is named mdworker_shared and lives in /System/Library/Frameworks/CoreServices.framework/.../Metadata.framework/Versions/A/Support/. You may still see plain mdworker in older guides.

Why it uses CPU

• Lots of new files: cloning repos, npm install, unzipping, copying photos. Every file is read once.
• Huge or complex files: big PDFs, Office documents, and archives take seconds each.
• A broken importer: a third-party .mdimporter that hangs or loops on its own file type.
• A file that changes constantly: a log or database rewritten every few seconds gets reimported every time.

How to make it calm down

First, find what it is reading:

sudo fs_usage -w -f filesys mdworker_shared | grep -v /System | head -40

If the paths are all in one project or cache folder, exclude that folder in System Settings › Spotlight › Search Privacy (Sonoma: Siri & Spotlight › Spotlight Privacy).

List the installed importers and look for third-party ones:

mdimport -L 2>&1 | grep -v /System/Library

Importers live in /Library/Spotlight, ~/Library/Spotlight or inside app bundles. Removing or updating the app that ships a misbehaving one fixes it. To test whether a single file is the problem:

mdimport -d1 ~/path/to/file.pdf

If it takes a long time or errors, that file (or its importer) is your culprit.

When to worry

Real workers run from the Metadata framework path above, under your user, _spotlight or root. Check one:

ps -o user,pid,etime,command -p $(pgrep -n mdworker_shared)

A worker with etime of hours is stuck; quit it in Activity Monitor and Spotlight will spawn a fresh one. A process called mdworker running from your Downloads, /tmp or a hidden folder in your home directory is not Apple’s and should be checked with codesign -dv --verbose=2 <path>.

Seeing it in Stat Space

Stat Space files macOS daemons like mdworker_shared under one System group in the Apps tab, so twenty workers don’t push your real apps off the list. Expand the group and tap a process to see its user, parent, uptime, signature and open files: the open files list is often enough to see which document a stuck worker is chewing on.