Maximum Datafile Size In an Oracle Database

Each Oracle datafile can contain maximum 4194303 (4 Million) data blocks. So maximum file size is 4194303 multiplied by the database block size.

Block Size | Maximum Datafile Size
———————————————
2k 4194303 * 2k = 8 GB
4k 4194303 * 4k = 16 GB
8k 4194303 * 8k = 32 GB
16k 4194303 * 16k = 64 GB
32k 4194303 * 32k = 128 GB

In Oracle Database 10g, BIGFILE tablespace was introduced. The BIGFILE tablespace can ONLY have a single datafile, but this datafile can contain maximum 4294967295 (4 billion) data blocks.

Block Size | Maximum Datafile Size
———————————————
2k 4294967295 * 2k = 8 TB
4k 4294967295 * 4k = 16 TB
8k 4294967295 * 8k = 32 TB
16k 4294967295 * 16k = 64 TB
32k 4294967295 * 32k = 128 TB

How to Select a Random Row

I’ve seen similar questions in programming forums about how to select a random row from a table. Most RDBMS have functions to generate random numbers, so with a simple query we can select a random row(s):

The above command will sort the HR.EMPLOYEES table in random order, so we’ll be able to select a random. If you want to limit the number of returning rows, you can use subquery method:

How to Import Data from XML

One of my blog readers asked me how to import data from XML file. There are lots of ways to do it but I’ll show only a simple one by using DBMS_XMLSTORE.

We will need a simple XML file to import. So I created a folder as “/oracle/xmltest” and a text file named (sample.xml) in this folder. Oracle should be able to access this folder and file, so check OS permissions of them and be sure that they are readable by oracle user.

I entered the followed data into my sample xml file:

As you see, our employees have only 2 properties, “no” and “name”. So I’ll create a table to store these properties:

Oracle Table Functions

A table function is a PL/SQL function which will behave like a row source when queried. So you can perform transformations to the data before it is returned in the result set.

To write a table function, first we need to define an object as the row structure:

Because our function will return a table, we’ll also define a type:

How to Move a Datafile to Different Location

If the database is in archivelog mode, you can move the datafile while database is up. Take the datafile offline, copy (or move) the datafile to the new location:

Then issue the following commands to rename the datafile and make it online:

If the database is in no archivelog mode, you need to shutdown the database, open the database in mount mode and copy/move the datafile:

Then rename the file and open the database: