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B*Tree Reverse index

B*Tree Reverse index is one of the index types that is supported by oracle. It more or less behaves like b*tree unique & non-unique index but only difference is the way it constructs the tree. In this index, index value is stored in the reverse direction when compared to the values in the actual data table. This index is used in order to distribute the index data evenly across all the leaf index nodes if table data is skewed very high. Like b*tree index, this index doesn’t understand NULL. This B*Tree Reverse index can be created on a single column or more than one column. More than one B*Tree Reverse index can be created for the same data table. HOW TO VERIFY: How to verify whether the created index is reverse index or not? Fire this query, select index_type from user_indexes where index_name = 'DEPT_ID_INDX' ð This query would return “ NORMAL/REV ” (it means it is B*Tree index but of “Reverse” type) LITTLE-KNOWN FACTS TO BE REMEMBERED: · ...

Listener refused the connection due to NetException

I was testing some piece of code for calculation of new date on the basis of a given pattern and the specified date. I wrote a method to automate the test cases to generates those patterns and calculate the new date for each date of the specified date of the range of years. Since there were around 1 million pattern test cases are possible, so I want to insert this data in database for any future reference. After creating a pattern I was inserting data of the pattern and the calculation date along with the calculated date. It was working fine. I was prepare to hit the start button now, after testing different patterns individually. I hit the run button and it started its executions, but in the middle, I got this error. java.sql.SQLException: Listener refused the connection with the following error:ORA-12516, TNS:listener could not find available handler with matching protocol stack at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:4...

Hash Natural Join

To perform hash join, Oracle follows these steps: 1. Oracle chooses the smallest of two tables as the hash table (otherwise called as driving table). Oracle built the hash table in RAM after applying the hash function on the joining column(s) of the driving table. 2. Oracle chooses the other [big] table as the probe table (otherwise called as driven table or probing table). It traverse through all the records of this probe table, applies the same hash function on the joining column(s) [column(s) used to join these two tables] and will hit the corresponding entry in the hash table. 3. Oracle returns the output if a record from driving table is already present in the same hash key, else no record will be returned. It may look like Nested loop join & Hash join have the same architecture since both these have the concept of driving & driven tables but they have entirely different design if you closely look a...

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