Creating an Index in Oracle and Forward Vs. Inverted Index
Indexes may sound confusing and complicated at first, especially when database professionals talk about strategies concerning them. However, they are actually quite straightforward due to their purpose and usage.
For those new to Oracle, databases, or both, all you have to do is understand what indexes are and how to use the ones in most common use. It is also important to be aware of the differences among these. In this article, we will briefly explain a few of these and how DBAs use them.
First, let us take a look at some of the features that indexes are created according to. Database experts can create index oracle of both types, unique and non-unique. The database ensures a unique index for two types of constraints – Primary Key and Unique Key.
In case there already are multiple non-unique indexes present on a column with a primary key, the database will not make another index even if you are trying to create a unique one. The index can cover a single column or several columns according to the specific requirement.
When they are based on more than one column, the indexes get a new name – Composite Indexes. This type of index is capable of fetching information at a faster rate with the use of SELECT queries. Therefore, these help with Oracle query performance tuning and improvement. The statements, however, must have a WHERE clause that contains a reference to some or most of the columns that are present in the composite index.
DBAs also create some indexes on the basis of function. The information present in the columns of such indexes depend on computations. An Application Domain index is another variant of indexes. As its name suggests, it finds use in applications of certain specifications, such as spatial or text applications.
What is a Forward Index?
The database can build an index in different ways. One of the most common ones is by saving a list that consists of every term present in the document for which the database is creating an index. This technique creates a forward index that is quite rapid in its operation. This is because it doesn’t need rebuilding; new documents just attach themselves to it.
On the other hand, its efficiency is not as good during statement execution, ultimately resulting in the use of an Oracle query optimizer tool. This is due to the search engine that has to visit each entry in the index to locate the piece of information it requires.
What is an Inverted Index?
Speeding up the process of statement execution requires a different approach. In some cases, sorting the index on the basis of the data leads to quicker results. This type of index is called an inverted index due to its inverted method of indexing as compared to that of the forward index.
The inverted index makes things simpler as well since the DBA only has to go through the list once to fetch the necessary term and retrieve a list containing every unit in possession of the term.
How are Both These Indexes Useful?
Both these indexes are useful in search engines and the database can create index Oracle by sorting the forward index using its terms. Some search engines have indexes that provide more data regarding one or more parameters, such as the frequency of occurrence of certain information.
They may also shed light on the location of that data within every document or unit. The number of times the term shows up becomes part of calculations that help determine the relevance of search results. The position, on the other hand, helps the search engine locate particular phrases within a document.
In fact, there are countless hints and strategies discussed in forums for users and DBAs to analyse their indexes and tables. Aside from maintaining accurate and up-to-date statistics, you must regularly test the statements you create, especially if they are new.
The Explain Plan mechanism can help with this and the optimisation of your Oracle database and SQL to decrease the overall number of resources used. Working on the reduction of computational data merging and sorting will give you a good start on the journey to better performance.
Author Bio: Tosska Technologies is a company that focuses in providing solutions for database and SQL related performance optimization and improvements. Our mission is to help users to smooth out the hurdle by our new technologies.