v$sort_segment behavior in 10g and 11g database

Hi Experts,

I have a customer who is having following question regarding behaviour of v$sort_segment.free_block column

Based on experiences from 10g the customer constantly monitors v$sort_segment.free_blocks of all the instances.

In 10.2, if this value decreased to zero, it typically caused ORA-1652: unable to extend temp segment by 128 in tablespace TEMP.

Now, in 11.2, though various database instances intermittently return v$sort_segment.free_blocks = 0, we do not observe any ORA-1652.

Moreover, the customer has more 11.2 database, but just this one intermittently returns v$sort_segment.free_blocks = 0.

The question is whether v$sort_segment.free_blocks = 0 indicates any possible problem or whether it is just a change of TEMP behavior between 10.2 and 11.2. Or what else may it mean.