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PostgreSQL Upgrades are hard!

Together with Lætitia Avrot and Nikolay Samokhvalov I was invited to participate in a Community Panel (YouTube video) about PostgreSQL Upgradability at Postgres Vision 2022. The panel was moderated by Bruce Momjian and initiated and organized by Jimmy Angelakos. Bruce did talk with each of us before, which helped a lot to guide the discussion in the right direction. The recording of the panel discussion is available on the Postgres Vision website.

During this panel each of us provided examples for how easy or complicated PostgreSQL upgrades still are.
 

 

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PostgreSQL Project @ GSoC 2022

As is a good tradition, the PostgreSQL Project participates in Google Summer of Code (GSoC). Last year we submitted 7 projects for 7 students - and got all 7 projects accepted. This year we got quite a few more good proposals from students, and more mentors are helping. Guess what? Google accepted all 12 proposals!

Google modified the program again. For 2021 they cut the time for every project in half, to accommodate for the at-home work during the Covid-19 pandemic. This turned out to be suboptimal, and many larger projects need more time. This year students can choose between “medium” (175 hours) and “large” (350 hours) projects. This gives everyone a chance to scope the project accordingly.

 

 

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My PostgreSQL database is empty!

The one thing I like to do is challenge PostgreSQL - and readers - to the extreme. A while ago I posted about the Beer o'clock. Building Zoé was another interesting example. And at some point I blog about Dancing with the Stars as well. Today it's all about nothing. Empty. Where is all the data gone?

A while ago I posted this screenshot on Twitter, and as far as I can tell no one found the correct answer.

The screenshot looks like there's nothing. Empty names, schema name, role name, database name, even no data. And yet this all comes together and somehow works. Let's dig in.

 

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Hugo: Count entries in Taxonomy

For the "PostgreSQL Person of the Week" interviews I'm using Hugo as static blogging engine. Part of every interview is the list of tags, which links this interview to other similar interviews. However until recently no one really knew if a tag is popular or just used in this interview. I wanted to change this, and add the tag count behind every tag.

The way I use Hugo I have the previews also online, and I don't want to count any interviews which are not published (still drafted) when counting entries for a tag.

Tags in Hugo are taxonomies, which is a user-defined grouping of content.

 

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Google Sheets: Format cell background based on a value in a cell in another sheet

My problem: sometimes I forget to review published interviews for a talk.

I publish a weekly interview series, the "PostgreSQL Person of the Week" interviews. The data lives in a big spreadsheet, which has several sub-sheets.

The first one, the main sheet, is holding the overall status of all interviews, and has one column which indicates if the interview is complete.

Another sheet, the fifth one, holds the statistics data for my talk about what I learned interviewing the community.

The first column in the fifth sheet is copying the name from the first sheet. The second column indicates if I already looked over the interview and gathered all the statistics. And this is where today's problem came up: whenever I finished an interview (over 100 of them already) I marked this second column with a question mark ("?") to let myself know that at some point I need to read the interview again. But of course I don't always remember to do that.

My idea was to color the background of this cell, based on the value in the first sheet: make the cell background green when the interview is completed. This gives me an instant indication if I need to work on this interview or not.

Turns out this is a bit complicated, but possible.

 

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Read a JSON text into a variable in Ansible without parsing it

For one project I need to insert the content of a local file into another file on the remote system, and the first file happens to be JSON. The JSON file is in compact format (jq --compact-output) and is supposed to stay this way. When Ansible reads the content of the file, it determines that the content is JSON, and parses the content into the variable - and along the way is uncompressing the format. Not what I want.

 

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Does an openHAB Item exist?

In a more complex openHAB2 Rule I'm writing, I need to find out if a certain Item exist. If I try to access it when it does not exist, the Rule will fail. Not good.

I could pass in a parameter to the framework which builds the Rule, but that is cumbersome and requires changes on several places.

Let's see if I can have the Rule figure this out.

 

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Hanging script at the end of Python multiprocessing

While writing and stress-testing a Python script which uses the multiprocessing library, I ran into the problem that occasionally the script hangs at the end. Literally runs past the last line of code and then hangs.

In this script I'm using Queues and Events, so I made sure that I properly close the queues in the forked/spawned (tried both) processes and also clean out all queues in the parent. Nevertheless occasionally - like seldom, but it happens - the script hangs. Checked the process list, checked remaining threads, checked the queues, all fine. Still ...

When I hit Ctrl+C, I get the following stack trace:

^CError in atexit._run_exitfuncs:
Traceback (most recent call last):
  File "/usr/lib/python3.9/multiprocessing/util.py", line 300, in _run_finalizers
    finalizer()
  File "/usr/lib/python3.9/multiprocessing/util.py", line 224, in __call__
    res = self._callback(*self._args, **self._kwargs)
  File "/usr/lib/python3.9/multiprocessing/queues.py", line 201, in _finalize_join
    thread.join()
  File "/usr/lib/python3.9/threading.py", line 1053, in join
    self._wait_for_tstate_lock()
  File "/usr/lib/python3.9/threading.py", line 1073, in _wait_for_tstate_lock
    if lock.acquire(block, timeout):
KeyboardInterrupt

(Can't change the Python 3.9, as I don't control the target system where this is supposed to run)

There's nothing left to join, the only two remaining threads are MainThread and QueueFeederThread.

 

After some more debugging I had the simple idea not only to empty the queue before finishing the script, but setting the queue variable to None:

worker_queue = None

This helps. The script is no longer hanging at the end. At a later point I will see if the problem is fixed in newer versions.