How to find what is locking a table.

- How to find what is locking a table.
       1. Query from DBA_OBJECTS to find the object_name of the table getting locked.
       2. Query from V$LOCK where id1 = 'table_name', get sid.
       3. Query from v$PROCESS where pid = sid. THis has info on what is locking the table.

Select Randomly from Table
This feature allows you to randomly "sample" from a table. This feature has many great uses. The syntax is as follows:
SELECT COUNT(*) * 100
FROM EMP SAMPLE (1);
This will randomly sample 1% of the rows, multiple the count of them x 100 to get a rough estimate of the amount of rows in the table.
You can also randomly sample by blocks for better performance but possibly less random:
SELECT *
FROM EMP SAMPLE BLOCK (1);
Again, this samples roughly 1% of the table by blocks, which may not be 1% of the actual rows. But this will cause fewer blocks to be visited and decrease the elapsed time, but if the data is grouped in the table, it may not be very random.
This tool can be used to get a rough idea of the data in the table, or give good estimates when using group functions. For example, a great use of this would be on a 40 million row table:
SELECT AVG(number_of children) * 20
FROM dependants sample (5);
This will give you an average of the number of dependants by only sampling 5% of the table by only visiting 2 million rows and not 40 million.