Parameters of Purge command

[shoffmanHLUYT]

What parameters does AutoCAD Elec use when deciding if a purge command will detect anything in a drawing? Seems like a few changes to a simple drawing may not result in a purge. A lot of changes may. Or not. How does ACE measure these changes to decide if a purge is worth its time? Does file size trigger this e.g. the original file is X units large but ACE won't allow a purge until the file size changes to X - Y? If so, what is the value of Y? It is, perhaps, a ratio of objects in the drawing to deleted objects? Are there other calculations that define when a purge will be allowed? Maybe the type of changes matter, for instance, deleting blocks might count more than deleting simple text objects? Or is it a combination of changes that give the go-ahead for a purge command to proceed?

[rhesusminus]

AutoCAD (Electrical) will never purge anything. Nothing is triggered.
A purge means "remove stuff from the drawing that's not used anymore."
You can create 5 million layers in a drawing if you want to, but if you don't draw anything on those layers, they're pretty useless and can be purged.

When you insert a block into a drawing, a block definition is saved to the drawing database, and what you see in the drawing are references to that block definition. If you remove all instances of the block references, the block definition is still in the drawing database and can also be purged, as they're not used anymore.

And so on, and so on.

When it comes to "automatic filesize," we have the ISAVEPERCENT variable. Every time you save the drawing, all changes are just added to the end of the file to save time when saving large drawings.
If the ISAVEPERCENT is set to 50, AutoCAD will keep adding to the end of the file until all the stuff added is more than 50% of the original filesize. Then, AutoCAD will do a "full" save, and the filesize is smaller again.

[Thomas.CoxTFXY8]

I have a little lisp routing I use, it saves me time when purging (attached).  I'm sure it can be tweaked for your own type of use.  If you use a lot of preset layers that haven't been used yet they will disappear as Trond mentioned, hence why I also have a "layer state" saved externally.

[shoffmanHLUYT]

I just created a new drawing in AE, saved it, added some text, deleted the text, saved again, and tried Purge. Nothing happens. AE doesn't offer to purge anything. So there must be  a set point (of what?) that lets the purge command go forward. But what is it that AE uses for that set point? Is it related to that ISAVEPERCENT variable you mentioned?

[shoffmanHLUYT]

Maybe I see it now. Deleting a text object leaves nothing behind in the drawing file so there is nothing to purge. But deleting a block leaves behind the block definition, which is what gets purged. Is that it?

[rhesusminus]

Yup!

[rhesusminus]

If you look at the purge dialog window, you can see on the left side what kind of objects that can be purged.