Which schema is using the most disk space?

I was faced with interesting problem. Which schema, in my DB, uses the most disk space? Theoretically it's trivial, we have set of helpful functions:

  • pg_column_size
  • pg_database_size
  • pg_indexes_size
  • pg_relation_size
  • pg_table_size
  • pg_tablespace_size
  • pg_total_relation_size

But in some cases it becomes more of a problem. For example – when you have thousands of tables …

Continue reading Which schema is using the most disk space?

I have PostgreSQL, loaded some data, and have app using it. Now what?

I had to deal with this question, or some version of it, quite a few times. So, decided to write a summary on what one could (or should) do, after data is in database, and application is running. Namely – setup some kind of replication and backups.

What to use, how, and why? This is what this post is all about.

Continue reading I have PostgreSQL, loaded some data, and have app using it. Now what?

How much RAM is PostgreSQL using?

(disclaimer: all the data and examples in here are on Linux – the same data can be probably obtained on other systems too, it's just that I work on Linux and don't know other systems well).

This question pops occasionally in various places – PostgreSQL is using too much memory, why is that, and how can it be mitigated?

Before we can go to “optimizing", we should understand the problem. But do we? Both standard tools – ps and top – lie. How/why? Let's see.

Continue reading How much RAM is PostgreSQL using?

How to let clients to create new users?

Some (quite long) time ago, someone, somewhere (my memory is pretty fragile) asked a question. I don't have it exact, but the gist was: is it possible to give some users rights to create new users, without making them superusers, and forcing new users to have access only to one particular database.

After some discussion it was clear that the scenario was shared hosting with PostgreSQL, so the situation could look like this:

you are administrator of shared hosting service. One of services is PostgreSQL. You have client, named “depesz", and you want him to be able to create new users, but these users shouldn't be able to connect to any other database than depesz's db.

Is it doable?

Continue reading How to let clients to create new users?

Waiting for 8.5 – VACUUM FULL change

Some time ago Josh Berkus wrote about possible changes in VACUUM FULL.

Now these changes came to life. By now, I mean 6th of January, when Takahiro Itagaki committed his patch:

Log Message:
-----------
Support rewritten-based full vacuum as VACUUM FULL. Traditional
VACUUM FULL was renamed to VACUUM FULL INPLACE. Also added a new
option -i, --inplace for vacuumdb to perform FULL INPLACE vacuuming.
 
Since the new VACUUM FULL uses CLUSTER infrastructure, we cannot
use it for system tables. VACUUM FULL for system tables always
fall back into VACUUM FULL INPLACE silently.
 
Itagaki Takahiro, reviewed by Jeff Davis and Simon Riggs.

Continue reading Waiting for 8.5 – VACUUM FULL change

Who/what is trashing db performance?

Every so often I need to find who exactly is damaging database performance. I mean – I have db connection which does something strange/wrong with the database, but what exactly is responsible?

Switching to separate user for every program, script and developer would solve the problem, but it is not always an option. So, what should I do?

Continue reading Who/what is trashing db performance?