Why is Add Index grayed out?

[PaulHuffman]

I just loaded some NHD line feature classes and an EROM table into a Enterprise Geodatabase based on 10.3.1,  SQL Server 2012, and was going to make a join, but got the warning that there was no index built for the join attribute.  Went to my data owner connection in ArcCatalog 10.3.1, right click > properties>Indexes to add the index to the feature class, but found that add index is greyed out.  I saw that there is already an index for OBJECTID and an auto grid spatial index,  but can't figure out how I can add a new index.  Add Index is also grayed out with my sa and my sde connection.

The heck of it is that I did this a couple months ago at a different 10.3.1, SQL Server, ArcServer installation. I did a Remote Desktop via VPN to this other location,  inspected the properties of the same feature class with ArcCatalog, and saw that I had already built this index for this installation, and Add Index is not grayed out.  The Join is still working at this remote installation.

What did I forget to build on this current installation that is preventing me from adding my Index.

[JakeSkinner · Accepted solution]

Hi Paul,

If there is a lock placed on the feature class, this will prevent you from adding an Index.  For example, if you have the feature class published as a map service, or if someone else is accessing the feature class in ArcMap.

You can delete locks by connecting as an Administrator > right-click on geodatabase connection > Administration > Administer Geodatabsae > Locks tab.

[PaulHuffman]

Yeah, that was it.  I didn't think there would be locks because I just loaded the data, but I guess I forgot that I was looking at it in ArcMap trying to make the join which created locks.

[PaulDavidson1]

Interesting side note a number of years later.

I'm working in ArcPRO 2.4, same scenario, going to add a Join and warned about creating an index.  Been dong this long enough to know the index is not critical (usually....) but rarely hurt and the Attribute in question is in essence a primary key for us on many of our Feature Classes.

But in ArcPro, I'm not aware of any Admin Mode or any Right click to look at versions, etc...

Was just about to walk away, sort the data on the Attribute Key in question on the assumption the sort would help some.  Especially given that on the other Feature Class, I was able to add an Index to the Attribute Join key field.

For some reason I thought I'd try to rebuild the Spatial index.  Most  probably because it's staring me in the face there in ArcPro.  I also thought maybe there is an issue with the Spatial Index holding a lock on the file.

The Spatial Index rebuilt just fine and after it finished, there, lounging in anticipation of an eventful mouse click was the elusive button, all boxed in and ready to go 

 Add 

A quick mouse click later witnessed the creation of the critical indices.

Go Figure...