db: still needs definitions lec13: review

cst363/lec/lec12.md

@@ -1,4 +1,4 @@
-# lec11
+# lec12
 
 ## Lab
 

cst363/lec/lec13.md

@@ -15,4 +15,16 @@ Sorting the indexes allows us to search them _much faster_ than we could ever do
 
 Then we simply add a pointer to the index's list of associated pointers.
 
-It's important to note that indexes are tables, just like everything else in sql.
+The biggest problem we have with indexing that if have a large number of entries then we would end up storing a huge number of indexes and pointers.
+In order to avoid this, we don't take all of the entries.
+Instead of taking all entries we take instead every other entry into our index or even every third.
+This means that if we have a search that lands us inside one of the gaps we still search in a binary fashion but once we detect that we are we should search a _gap_ we linearly search through that gap.
+
+
+## Clustering 
+
+First let's recall that ideally our data entries in some table are physically located close to each other on disk _and_, are ordered somehow.
+
+### Dense Clustering
+
+### Sparser Clustering