Why do mds and mds_stores saturate the Mac’s CPU? How to solve it?

Probably if you’re on this article it’s because your Mac has been suffering from significant slowdowns for a while and has become almost unusable; it happened to me with the MacBook Pro i7 2008 with 16gb. By analyzing some performance data with “top”, I noticed that a particular process was saturating my MacBook’s CPU, causing the operating temperature of the computer to rise, consequently triggering the cooling system that constantly activated the fans.

The process guilty of this absurd slowdown was “mds_stores”. But what is it?

MDS stands for MetaData Server and is connected to Apple’s Spotlight.

For those who don’t know, the function of Spotlight on Mac and iPhone devices is to create an index of all the files present on your Mac or iPhone system. In practice, it takes care of indexing all the files to allow quick searches, there’s no doubt that it’s a very useful function that I often use, but not at the expense of the operation of the Mac itself.

When the “mds_stores” indexing starts, you can tell the process is active because in the upper right corner of the menu, on the “magnifying glass” icon, a dot should appear in the middle; this difference in the icon indicates that indexing is in progress and could therefore be a good indicator to understand if the slowdown phenomenon is closely related to the file indexing process.

In the meantime, if you want to know how long you’ll have to suffer from the slowdown, you can check the necessary time for indexing by clicking on the Spotlight icon.

In this way, it will be possible to know the current state of indexing and the remaining time for its completion.

Caution: When this process is running, it could use 100% of your Mac’s processor.

If you find yourself in these conditions, the process could slow down your Mac OS so much that you would not be able to do other work.

Remember that mds_stores activates during the addition or removal of data on the hard disk (or after the addition or removal of an external disk), therefore although the cause is easily identifiable, often it is not easy to understand the reason why the process is constantly activating. It could be related to apps writing data to the disk or some other cause, which almost always makes it necessary to investigate more deeply. In any case, it is always possible to at least temporarily disable the involved processes to understand if the cause of the slowdown is really connected to the indexing process. To do this, it will be enough to launch the following command from a terminal:

sudo mdutil -a -i off

This command disables file indexing and should return the system to normal behavior (reasonable CPU usage and fans off) after a short time.

In any case, to reactivate indexing, you will need to execute:

sudo mdutil -a -i on

To index your files you could activate the service at night. Be careful, the re-indexing will delete your Spotlight database forcing it to start over.