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The topic for this month's PGSQL Phriday blogging challenge is: pg_stat_statement. And Michael Christofides gave me a perfect opener in his invitation.

For anyone who doesn't know, I'm running a weekly interview series with people from the PostgreSQL community. It's called "PostgreSQL Person of the Week". One of the questions in the default set I give everyone is:

What is your favorite PostgreSQL extension?

And guess what the answer is: by far everyone's favorite is pg_stat_statements!

What does this extension do? It tracks statistics for planning and execution for queries run by users. This can be used to find long-running queries, users who run too many or too heavy queries, or just generate statistics about the workload. In short: very useful data. And the extension itself does not need a lot of resources. Even better.

This extension is so popular that it has double the interview mentions than the next one (which is PostGIS - by itself also a very popular extension). From the slides I occasionally present at conferences or meetups:

PostgreSQL has a lot of extensions, head over to the PostgreSQL Extension network (PGXN) which is operated by David E. Wheeler to find out about around 360 extensions. Currently in my interviews I have 51 different extensions mentioned.

This extension is so useful that people say:

• Julia Gugel: "I like pg_stat_statements as it helps a lot with performance troubleshooting."
• Daniel Westermann: "pg_stat_statements, because it is just required if you want to troubleshoot performance related issues. I still wonder why it comes as an extension and is not there by default."
• Lætitia Avrot: "Of course, I advise my customers to use pg_stat_statements to monitor their performance"
• Alexander Kukushkin: "The pg_stat_statements extension is something that everyone must enable for performance monitoring and troubleshooting."
• Flavio Gurgel: "I cannot live without pg_stat_statements, I think it’s mandatory for server optimisation."
• Anthony Nowocien: "pg_stat_statements and I will be glad to see it in core."

This is just a small selection of quotes, but this shows that everyone loves pg_stat_statements. I encourage you to head over and read more interviews. There's plenty of insight from community members.

This month's #PGSQLPhriday is hosted by Lætita Avrot, and she asks about triggers.

History time. Shortly after I started using PostgreSQL, I had a need to track changes in tables. Back then - this was the early version 7.x days - there was no such option available. I set out to write a tool for it. The logical choice to do that was to pick triggers to implement this. Today the world is different, PostgreSQL gained replication, and along with this, one can hook tools into the replication and stream all the changes. Back then there was no replication.

The second thing I discovered was that pl/pgSQL can't do the job. That was a rather big disappointment. My idea was to have one function which can be used with a trigger, the function figures out the columns and writes the changes into a separate table. However one can't access arbitrary column names in NEW and OLD in pl/pgSQL trigger functions. Something like this doesn't work:

columnname1 := "created_at";
columnname2 := "changed_at";

NEW.$columnname1 := OLD.$columnname1;
NEW.$columnname2 := OLD.$columnname2;

In pl/pgSQL, you have to "know" the column names in advance. Depesz recently posted some workarounds for this, but these options also have not been available back then.

Which made me write the tool in C. This at least allowed me to access the NEW and OLD values, and recoed changes. The tool is called "table_log", I also presented it at the first PGDay in Prato, Italy in 2007, and originally it was hosted on pgfoundry. This site is also long gone, I later copied the code to GitHub. But I also know that PostgreSQL 9.x had some internal changes which renders the tool non-working. However because the entire ecosystem had improved, and other tools are available, I did not update the old code anymore.

My conclusion: Triggers were one of the first "advanced" features I used in PostgreSQL, and I like them very much. They allowed me to implement an audit feature I need.

For this month's #PGSQLPhriday, Grant Fritchey asks: What is the one thing you wish you knew while you learn PostgreSQL.

My preferred client for PostgreSQL is psql, and while it is very powerful I like a few features a most:

• \timing
• \watch

Both are internal commands in psql, \timing is there for a very long time, but got improved at some point. \watch came later, but is also there for a couple years now.

Ryan Lambert asks in this month's PGSQL Phriday:

• What non-relational data do you store in Postgres and how do you use it?
• Have you attempted non-relational uses of Postgres that did not work well? What was the problem?
• What are the biggest challenges with your data, whatever its structure?
• Bonus: How do you define non-relational data?

Looking over the many databases we operate at work, I can say that we are mostly a "relational shop". Almost every database we have uses relational structures, and does not attempt to go in on "full NoSQL", or "store non-relational data". Many of the databases are on the larger size, often in the hundreds of GB or even several TBs. We have good people in our dev teams who understand both PostgreSQL and SQL, and can develop a proper schema for the data, and write performant queries.

There are a few exceptions though, but at least for us it's only a small number. Whenever we retrieve or get data which comes in from web requests, we may store this as JSON, and then we use JSONb. Quite often however it's rather "storage as JSON", not "querying the JSON in the database". It's just more convenient to keep the data in JSON format all the way, instead of transforming it several times.

Henrietta Dombrovskaya asks about Software Development and PostgreSQL. That's a very broad topic.

Not being a big developer for myself, and only occasionally submitting patches here and there, I nevertheless have a vast amount of data available on the topic: the "PostgreSQL Person of the Week" interviews! There are a few questions in the interviews which relate to this topic:

• Could you describe your PostgreSQL development toolbox?
• Which skills are a must have for a PostgreSQL developer/user?
• Do you use any git best practices, which makes working with PostgreSQL easier?
• Do you think PostgreSQL has a high entry barrier?
• What is your advice for people who want to start PostgreSQL developing - as in, contributing to the project. Where and how should they start?

And having 143 published interviews at this point, there is really interesting data about this topic. I picked two points which aim directly at developers:

Pat Wright is running this month’s #PGSQLPhriday, and the topic is “What is the PostgreSQL Community to you?”

The answer for me is very versatile, and covers quite a lot. Took me a moment to gather the facets, and likely I’m still missing some parts.
 

Last week for "PGSQL Phriday" I posted the following task:

Describe how you do backups for your PostgreSQL databases.

And I added a bonus question: Is pg_dump a backup tool?

Thanks to Ryan Booz we now have the #PGSQLPhriday blogging series. The second edition is about backups. And of course also about restore.

Backups? Do you need that?

If your data is not important, you certainly don't need to bother about backups. Then again, why do you even store the data in the first place?

For anyone else, especially everyone who runs business critical or mission critical applications, having a backup is important. Equally important, but sometimes ignored, is the ability to restore the backup.

The requirements for backups are manifold:

• How quickly must you be able to restore the backup (SLA)?
• Do you need to be able to restore every transaction (catch all changes) or is a snapshot (backup freuency, hourly, daily, weekly, monthly) sufficient?
• How can the backup integrity be verified? 
• Where do store the backup, and make sure that a disaster (as example: lost of data center) does not affect the backup?
• Who can restore the backup, what is the plan for that?
• ...

Your #PGSQLPhriday task

Describe how you do backups for your PostgreSQL databases.

Which tool(s) are you using, where do you store backups, how often do you do backups?
Are there any recommendations you can give the reader how to improve their backups?
Any lesser known features in your favorite backup tool?
Any new and cool features in a recently released version?

Bonus question: Is pg_dump a backup tool?

Uh, what is this #PGSQLPhriday thing about? Everyone is writing blog posts about this today ... For details, please read the introduction from Ryan Booz.

This month's topic: pick your three favorite or most important best pratices for #PostgreSQL. Tell them in a form that two are true, one is a lie. See if you can spot which one is true and which one is false. The resolution is at the end of this blog posting.

Let's dive in: These days it's rare that I start with a fresh PostgreSQL installation which is not in any way already modified. Whenever we install a new database at work, it's already coming with a templated configuration, backup (if necessary: despite running many hundred databases not all of them need a backup), monitoring, and pre-configured access. Even the database on my private laptop is configured using Ansible. But that's a good example by itself: what are the steps I find important enough to have a Playbook for. My top three list:

1. Change a few most important configuration parameters, then restart the database
2. Use pg_dump for backups
3. Create necessary accounts

Which one is the lie?