intro
In this blog, we explore clustered indexes in PostgreSQL. Tune in!
If you’ve ever built something using a database management system, you’ll surely be aware of indexes. In various database management systems, indexes have many types and PostgreSQL isn’t an exception — and once you’re well-acquainted with PostgreSQL, you will quickly understand that data types and indexes in PostgreSQL are something different altogether: the database management system is known for its exceptional and unparalleled support for various data types and indexes.
However, even with that in mind, many power users of PostgreSQL would be quick to point out that as far as clustered indexes go, PostgreSQL aims to use something that’d be vaguely similar to SQL Server, and yet comes up with something completely different: in PostgreSQL, the clustered attribute of the index is held in the metadata of the index in question itself.
Implementing Clustered Indexes in PostgreSQL
Searching for information about clustered indexes in PostgreSQL quickly confirms the fact that clustered indexes in PostgreSQL are different — many will be quick to point out that PostgreSQL, unlike MySQL and other database management systems, doesn’t have a direct implementation of clustered indexes. Instead, clustered indexes are implemented with a SQL query like so:
1
CLUSTER `table_name` USING `index_name`;
This CLUSTER PostgreSQL query lets us order data in a physical order with a couple of caveats:
One more thing to keep in mind is that the CLUSTER command isn’t the holy grail and it won’t solve any other performance issues your database may be facing — sure, a Postgres create index clustered strategy may help you with ordering the data in the table since that’s what it’s used for in the first place. Still, you have to keep in mind the points outlined above to make an educated decision.
Also, remember that using the CLUSTER command isn’t the only way to create ordered data sets and, according to the documentation, a query like so would work just fine on PostgreSQL:
1
SELECT `col1`, `col2`, `col3` INTO TABLE `some_table`
2
FROM `demo_table` ORDER BY `col1`;
In MySQL, we would use something like the following, but it’d also be possible:
1
INSERT INTO `some_table` (`col1`, `col2`, `col3`)
2
SELECT `col1`, `col2`, `col3` FROM `demo_table`
3
ORDER BY `col1`;
Beyond Clustered Indexes in PostgreSQL
After you’ve defined a clustered index or two, you’d likely be looking at other means to increase the performance of your queries, too. What if I told you that there are tools that have it all figured out on your behalf? That’s right — DbVisualizer is one of them. With support for over 50 database management systems, you will surely find your beloved PostgreSQL (or other database management system) in the list. Once you do, import data into the tool to start working with it, then start fiddling with your database of choice.
The listing of databases on the left side of the tool will help you figure out what database you need to be working with, and once you dive deeper into some statistic, you will also see it on the right-hand side. Below, you can see indexes existing on demo_table (we’ve selected this table on the left side):
From the outset, we can already see that we have two useless indexes because both of them have only 18 unique rows inside of them — we can then dive into the data inside of our table to find out why that’s the case to begin with (DbVisualizer will automatically limit the number of rows displayed to not crash if the number is high):
Interesting, isn’t it? And that’s just the tip of the iceberg. Try DbVisualizer for free for 21 days and fiddle with its powerful options for yourself — you won’t be disappointed.
Summary
Clustered indexes in PostgreSQL are implemented a little differently than in other database management systems like MySQL, SQL Server, or Oracle. While MySQL and its counterparts allow us to define a PRIMARY KEY as our clustered index, we will have to use the following query on PostgreSQL instead after we replace the table name and index name:
1
CLUSTER `table_name` USING `index_name`;
That’s not too bad though — understanding how Postgres create index clustered works will certainly be useful and beneficial both now and in your upcoming career steps as a developer or DBA.
We hope that this blog has taught you something new, stay tuned for more blog posts, and until next time.
FAQ
How to implement a clustered index in PostgreSQL?
A clustered index in PostgreSQL can be implemented like so after you replace table_name with the name of your table and index_name with the name of your index:
1
CLUSTER `table_name` USING `index_name`;
How do clustered indexes in PostgreSQL differ from clustered indexes in other database management systems?
PostgreSQL clusters data, but does not cluster changes to data, it can be slow at times, and the statement can cause you to lose grant permissions. Educate yourself on how it works and use it responsibly.
How are clustered indexes implemented in other database management systems?
Clustered indexes in other database management systems like MySQL are implemented as primary keys or in another fashion telling our database that there will be only one clustered index per table (we cannot define multiple clustered indexes.)
