mdworker (and mdworker_shared) high CPU on Mac, explained

mdworker and mdworker_shared are Spotlight's indexing workers: the processes that actually read your files to build the search index. High CPU almost always means indexing is in progress, and it normally finishes on its own. Here's what they do and when to step in.

What mdworker actually does

Spotlight indexing is split across a few processes, and it helps to know which is which:

• mds: the coordinator that watches the filesystem for changes.
• mds_stores: manages and writes the index database itself (the hidden .Spotlight-V100 store).
• mdworker / mdworker_shared: the short-lived workers that open each file, load the matching importer plugin, and extract text and metadata.

mdworker_shared runs those importer plugins inside shared, sandboxed worker processes, so several running at once is expected; that's parallel indexing, not a runaway.

Why it's using high CPU

Indexing kicks off, and the workers get busy, when:

• macOS just updated and Spotlight is re-indexing.
• You copied or added a large number of files.
• A new, external, or Time Machine volume is being indexed for the first time.
• The index is corrupt and being rebuilt.
• A single malformed file or a buggy importer plugin makes a worker crash-loop.

Is mdworker a virus?

No. Genuine Spotlight workers are Apple processes that live under /System/Library. Because indexing touches everything, malware has occasionally used similar-looking names, but real system daemons run from protected system paths, while impostors run from user-writable locations. If you're unsure, check the process's path before believing any "virus" claim.

What to do about it

1. Usually, wait it out. Indexing finishes and CPU drops, often within minutes, longer for big or external drives. Keep the Mac plugged in and idle.
2. Disconnect external / Time Machine disks while troubleshooting, in case one of them is what's being indexed.
3. Rebuild the index if it's stuck for days: sudo mdutil -E / erases and rebuilds it. You don't need to turn indexing off first; -E on its own is enough. (Check status any time with mdutil -s /, which needs no sudo.)
4. Exclude a problem folder in System Settings → Spotlight (on Sonoma and earlier, "Siri & Spotlight") → Search Privacy… (Sonoma and earlier: "Spotlight Privacy…").
5. Reboot or try Safe Mode, and keep macOS updated.

Note: % CPU over 100% is normal on multi-core Macs; each core counts as 100%, so a busy worker at 150% isn't alarming.

What people get wrong

Slowdowns blamed on mdworker are often really mds_stores, historically the more common culprit. And killing a worker won't fix a corrupt index; you have to rebuild it. If the CPU spike is part of a broader slowdown, work through why is my Mac slow to find the real cause.

See what's really working your Mac

When a background process spikes, the useful question is which one and whether it matters. Plumby shows live CPU in your menu bar with the process named in plain language and the fix beside it, so you can tell "Spotlight is just indexing, leave it" from "this needs attention" without digging through Activity Monitor. Every reading is measured from your Mac's real state.