Imaginary indexes created when setting CLOBs to null?

We've been testing a new application in development using CLOBS. The developer contacted me with following error:  

1]: (Error): ORA-01654: unable to extend index YURIY.SYS_IL0000185466C00023$$ by 256 in tablespace TS_EMAIL_CLOB  

The odd things here are that  

1. It occurred while updating the CLOB column to null (why would setting something to null *increase* the size of an index?)
2. The named index does not exist (implying it was something Oracle might have created on the fly?)

I increased the tablespace size and the problem went away but I'm trying to figure out what happened.  

The tablespace is one assigned to the CLOB segment. Oracle 8.1.7.2
Solaris 2.6  

Thanks,
Jay Miller Received on Wed Mar 19 2003 - 15:37:59 CST