What are the metadata.mds processes (Spotlight)?

2006-08-20 17:00

The metadata.mds family of processes powers Spotlight search on your Mac. If you have ever noticed your Mac running hot after an update, these processes are likely the reason.

What are the mds processes?

mds (metadata server): the core Spotlight indexing daemon that coordinates all indexing work
mdworker: worker processes that read and index file contents (you may see several mdworker instances running at once)
mds_stores: manages the Spotlight index database on disk
mdwrite: handles writing index updates to the Spotlight database

What do they do?

Spotlight keeps a searchable index of every file on your Mac. When you press Cmd + Space and type a search, Spotlight searches this pre-built index rather than scanning every file on disk in real time. The mds processes build and look after this index.

Why are they using so much CPU?

Heavy CPU use from mds processes usually happens when:

You have just run a macOS update (the whole index is rebuilt)
You have added many files at once (photo imports, downloading a project)
You have plugged in an external drive for the first time
The Spotlight index is damaged and needs rebuilding

This is short-lived. Once indexing catches up, CPU use drops to nearly nothing.

How to check indexing status

mdutil -s /

This shows whether indexing is on and its current status.

How to fix high CPU use that will not stop

If mdworker is stuck using CPU:

Try rebuilding the index: go to System Settings, then Spotlight, then Search Privacy, add your hard drive, then remove it. This forces a full re-index.
Or from the command line:

sudo mdutil -E /

Can you turn off Spotlight?

Yes, but it is not a good idea:

sudo mdutil -a -i off

This turns off indexing system-wide and breaks Spotlight search, Finder search, Siri knowledge, Mail search, and many other features.

Should you worry?

No. The mds processes are needed for search on macOS. High CPU use is brief during indexing. Once the index is up to date, they are barely noticeable.

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