I was trying to see the b-tree levels for indexes and to my surprise I see some of them are set to null.
SELECT index_name, blevel FROM user_indexes ORDER BY 2 desc;
Their name starts with "SYS_"(picture attached below). SO I am assuming they are system generated indexes? Maybe of primary keys? Either ways I am curious as to why they are null. I can understand if the value is 0 which mean everything is in leaf nodes and it will just take 1 hop for unique scan to get the data.
Best Answer
Indexes whose the name start with
SYS_IL..
are LOB indexes.BLEVEL
is a property of B-tree indexes, and does not make sense for LOB indexes.Even if you collect statistics,
BLEVEL
for such an index will remain null.