Why are there so many instances of mdworker running on El Capitan

Have you looked at the Spotlight Suggestions & privacy?

In Snow Leopard I put all of my folders into private area along with Caches from my library -- that seemed to help - as I never used it that much - and only realized it was indexing everything after my system jammed.

Seems they have been working on making a bad idea worse.

Normal.

Those processes will come and go depending on how much disk indexing is required at any given time. You may see as many as 50 (like I did the other day) and some 3 or 4 hrs later there were only 9. Then later still it was down to just 2.

So as was mention... it's kind of normal so don't get too concerned over it.

Don't know if they still show PID number in Activity Monitor (probably equivalent to job number on -- but if you display that and sort hight to low -- see how rapidly the numbers increment - I have only folder checked on the search -- along with my folders so I don't see that much activity and it never stays long.

The jobs may still have to be called without actually doing anything other than - okay don't have to do that - so its in and out rather than having to index whatever.

BarryXSharp wrote:

Those processes will come and go depending on how much disk indexing is required at any given time. You may see as many as 50 (like I did the other day) and some 3 or 4 hrs later there were only 9. Then later still it was down to just 2.

So as was mention... it's kind of normal so don't get too concerned over it.

These jobs are setting up the index for Spotlight - as opposed to the regular directories. Never really used it - and it does reach a point where it can jam up your system - no problems for years until....