TWID Feb 25, 2019: Galaxy Fold, Huawei Mate X, Hololens 2, Juventus, Linux Fsync Issue fix for PostgreSQL, syrup

This is a post detailing some stuff I did, learned, posted and tweeted this week, I call this TWID (This week in Denis). I am doing this mostly for myself... a kind of an online journal so that I can look back on this later on. Will use the label TWID for these

This Week I Learned

Almost finished with the book The Annotated Turing: A Guided Tour Through Alan Turing's Historic Paper on Computability and the Turing Machine by Charles Petzold

It takes a lot of maple sap to create maple syrup.  The higher the sugar content of the sap, the smaller the volume of sap is needed to obtain the same amount of syrup. 57 units of sap with 1.5 percent sugar content will yield 1 unit of syrup, but only 25 units of sap with a 3.5 percent sugar content are needed to obtain one unit of syrup

Those are my youngest two trying the sap. I tried it as well, I must say there really is no taste to it.

I will make a separate post about our visit to the farm

This Week I Tweeted

Samsung’s foldable phone is the Galaxy Fold, available April 26th starting at $1,980

Samsung first teased its foldable phone back in November, and at the company’s Galaxy Unpacked event today, it’s further detailing its foldable plans. Samsung’s foldable now has a name, the Samsung Galaxy Fold, and the company is revealing more about what this unique smartphone can do. Samsung is planning to launch the Galaxy Fold on April 26th, starting at $1,980, through AT&T and T-Mobile in the US, with a free pair of Samsung’s new wireless earbuds. There will be both an LTE and 5G version of the Galaxy Fold, and Samsung is even planning on launching the device in Europe on May 3rd, starting at 2,000 euros.

Overpriced and if you damage a screen how much to repair this. I rather have a phone like the showed in the Expanse or even better a phone you can roll up so it is the size and shape of a pen. This thing is just too bulky as well. A better design would have been if there was a screen that you could slide out instead.

If you thought the Galaxy Fold was not expensive enough.. no worried The Mate X is Huawei’s 5G foldable phone... the price $2600.  Fitting name Mate X, as in mate you will need eXtra money for this one... 

Pass on both from me


Juventus share price is down 9% after their champions league result

  Ouch, that is not good, but Atletico played a much better 2nd half and converted their chances. Let's see if Juve can advance by scoring at least 2 at home in the return game.


Falsehoods Programmers Believe About Phone Numbers 

Some interesting things you might already know, still good to revisit this list

Some cool stuff you might enjoy

Microsoft’s HoloLens 2: a $3,500 mixed-reality headset for the factory

The Microsoft HoloLens 2 is available for preorder today for $3,500, and it’s expected to ship later this year. However, Microsoft has decided that it is only going to sell to enterprise customers who want to deploy the headset to their workers. As of right now, Microsoft isn’t even announcing a developer kit version of the HoloLens 2.

Compared to the HoloLens we first saw demonstrated four years ago, the second version is better in nearly every important way. It’s more comfortable, it has a much larger field of view, and it’s better able to detect real physical objects in the room. It features new components like the Azure Kinect sensor, an ARM processor, eye-tracking sensors, and an entirely different display system.

It has a couple of speakers, the visor flips up, and it can see what your hands are doing more accurately than before. There’s an 8-megapixel front-facing camera for video conferencing, it’s capable of full 6 degrees of tracking, and it also uses USB-C to charge. It is, in short, chock-full of new technology. But after four years, that should be no surprise.


Linux Fsync Issue for Buffered IO and Its Preliminary Fix for PostgreSQL

One of the common fixes applied to all the supported PostgreSQL versions is on – panic instead of retrying after fsync () failure. This fsync failure has been in discussion for a year or two now, so let’s take a look at the implications.

A fix to the Linux fsync issue for PostgreSQL Buffered IO in all supported versions
PostgreSQL performs two types of IO. Direct IO – though almost never – and the much more commonly performed Buffered IO.

PostgreSQL uses O_DIRECT when it is writing to WALs (Write-Ahead Logs aka Transaction Logs) only when wal_sync_method is set to : open_datasync or to  open_sync with no archiving or streaming enabled. The default  wal_sync_method may be fdatasync that does not use O_DIRECT. This means, almost all the time in your production database server, you’ll see PostgreSQL using O_SYNC / O_DSYNC while writing to WAL’s. Whereas, writing the modified/dirty buffers to datafiles from shared buffers is always through Buffered IO

Starting from kernel 4.13, we can now reliably detect such errors during fsync. So, any open file descriptor to a file includes a pointer to the address_space structure, and a new 32-bit value (errseq_t) has been added that is visible to all the processes accessing that file. With the new minor version for all supported PostgreSQL versions, a PANIC is triggered upon such error. This performs a database crash and initiates recovery from the last CHECKPOINT. There is a patch expected to be released in PostgreSQL 12 that works for newer kernel versions and modifies the way PostgreSQL handles the file descriptors. A long term solution to this issue may be Direct IO, but you might see a different approach to this in PG 12.

Some more info that I found in this hackernews comment thread that might interest you:
If you want an overview of the issue, here's a presentation from Tomas Vondra at FOSDEM 2019: https://youtu.be/1VWIGBQLtxo
Or an early recap of the "fsyncgate" issue in textual form: https://lwn.net/Articles/752063/

Related (also listed by Tomas Vondra): Linux's IO errors reporting https://youtu.be/74c19hwY2oE


As always, I will leave you with a pic I took this past week. This one is a pic of some orange roots over a stream

Calculating Sexy Primes, Prime Triplets and Sexy Prime Triplets in PostgreSQL

The other day I was reading something on Hackernews and someone posted a link to a Sexy Primes wikipedia article.  I looked at that and then decided to do this in SQL Server because.. why not? Then I decided to see how different this would be to do in PostgreSQL.  For the first method to create the prime numbers it's different. For the method with the CTE it is very similar


From the Sexy Primes wikipedia link: https://en.wikipedia.org/wiki/Sexy_prime


In mathematics, sexy primes are prime numbers that differ from each other by six. For example, the numbers 5 and 11 are both sexy primes, because 11 minus 5 is 6.

The term "sexy prime" is a pun stemming from the Latin word for six: sex.

If p + 2 or p + 4 (where p is the lower prime) is also prime, then the sexy prime is part of a prime triplet.

Ok I did a couple of versions of this and over the weekend.. here is what I ended up with

So first we need a table that will just have the prime numbers

I decided to populate a table with numbers from 2 till 500 and then use the sieve of Eratosthenes method to delete the non primes

This will look like this

Create this table

CREATE  TABLE  PrimeNumbers  (N INT);

In one window run this to create the function/proc

CREATE OR REPLACE FUNCTION MakePrime() RETURNS void AS $$
DECLARE I integer := 2;
BEGIN
WHILE I <= SQRT(500) LOOP
    DELETE FROM PrimeNumbers WHERE N % I = 0 AND N > I;
    I := I + 1 ; 
END LOOP;

END;

$$ LANGUAGE plpgsql;

In a another window populate the table by making the call to the function
 

INSERT  INTO PrimeNumbers(n)
SELECT N
 FROM (SELECT generate_series(2,500) as n) x;


SELECT MakePrime() ; -- Yes that is a proc call

SELECT * FROM PrimeNumbers

Thinking about it a little more I decided to do it with a CTE instead of a loop with delete statements, if your tables will be big then the delete method is probably better... it's for you to test that out :-)

What we are doing is a NOT EXISTS query against the same cte and we are filtering out numbers that are greater than the number in the current row and are not divisible by the current number

CREATE TABLE IF NOT EXISTS  PrimeNumbers  (N INT);


;WITH cte AS (
  SELECT * FROM generate_series( 2, 500 )  n
  )

INSERT INTO PrimeNumbers
SELECT n
FROM cte
WHERE NOT EXISTS (
  SELECT n FROM  cte as cte2
WHERE cte.n > cte2.n AND cte.n % cte2.n = 0)
;

SELECT * FROM PrimeNumbers;

If we run that last select statement, we should have 95 rows

2
3
5
7
 .....
 .....
463
467
479
487
491
499

Now that we have our table filled with prime numbers till 500, it's time to run the queries

Sexy prime pairs
The sexy primes (sequences OEIS: A023201 and OEIS: A046117 in OEIS) below 500 are:

(5,11), (7,13), (11,17), (13,19), (17,23), (23,29), (31,37), (37,43), (41,47), (47,53), (53,59), (61,67), (67,73), (73,79), (83,89), (97,103), (101,107), (103,109), (107,113), (131,137), (151,157), (157,163), (167,173), (173,179), (191,197), (193,199), (223,229), (227,233), (233,239), (251,257), (257,263), (263,269), (271,277), (277,283), (307,313), (311,317), (331,337), (347,353), (353,359), (367,373), (373,379), (383,389), (433,439), (443,449), (457,463), (461,467).


Here is that query for the sexy prime pairs

-- 46 rows.. sexy primes
SELECT t1.N,t2.N 
 FROM PrimeNumbers t1
join PrimeNumbers t2 on t2.N - t1.N = 6 
order by 1

It's very simple.. a self join that returns rows where the number from one table alias and the number from the other table alias differ by 6




Prime triplets
The first prime triplets below 500 (sequence A098420 in the OEIS) are

(5, 7, 11), (7, 11, 13), (11, 13, 17), (13, 17, 19), (17, 19, 23), (37, 41, 43), (41, 43, 47), (67, 71, 73), (97, 101, 103), (101, 103, 107), (103, 107, 109), (107, 109, 113), (191, 193, 197), (193, 197, 199), (223, 227, 229), (227, 229, 233), (277, 281, 283), (307, 311, 313), (311, 313, 317), (347, 349, 353), (457, 461, 463), (461, 463, 467)

A prime triplet contains a pair of twin primes (p and p + 2, or p + 4 and p + 6), a pair of cousin primes (p and p + 4, or p + 2 and p + 6), and a pair of sexy primes (p and p + 6).

So we need to check that the 1st and 3rd number have a difference of 6, we also check that that difference between number 1 and 2 is 2 or 4.  That query looks like this

-- 22 rows.. Prime Triplets
SELECT t1.N AS N1,t2.N AS N2, t3.N AS N3
 FROM PrimeNumbers t1
join PrimeNumbers t2 on t2.N > t1.N 
join PrimeNumbers t3 on t3.N - t1.N = 6
and t3.N > t2.N
and t2.n - t1.n IN (2,4)
order by 1

Here is what it looks like from pgAdmin

Sexy prime triplets
Triplets of primes (p, p + 6, p + 12) such that p + 18 is composite are called sexy prime.  p p, p+6 and p+12 are all prime, but p+18 is not

Those below 500 (sequence OEIS: A046118) are:

(7,13,19), (17,23,29), (31,37,43), (47,53,59), (67,73,79), (97,103,109), (101,107,113), (151,157,163), (167,173,179), (227,233,239), (257,263,269), (271,277,283), (347,353,359), (367,373,379)


The query looks like this.. instead of a self join, we do a triple self join, we also check that p + 18 is not a prime number in the line before the order by

-- 14 rows.. Sexy prime triplets
SELECT t1.N AS N1,t2.N AS N2, t3.N AS N3
 FROM PrimeNumbers t1
join PrimeNumbers t2 on t2.n - t1.n = 6
join PrimeNumbers t3 on t3.N - t1.N = 12
and t3.N > t2.N
AND NOT EXISTS( SELECT null FROM PrimeNumbers p WHERE p.n = t1.n +18)
order by 1

And that's it for this post.  If you are interested in the SQl Server version, you can find it here: Calculating Sexy Primes, Prime Triplets and Sexy Prime Triplets in SQL Server


More PostgreSQL posts can be found here:  /label/PostgreSQL

TWID Feb 18, 2019: Bruno Ganz, Red hat dropping MongoDB, 500px hacked, VFEmail

This is a post detailing some stuff I did, learned, posted and tweeted this week, I call this TWID (This week in Denis). I am doing this mostly for myself... a kind of an online journal so that I can look back on this later on. Will use the label TWID for these

This Week I Learned

Continued reading the book The Annotated Turing: A Guided Tour Through Alan Turing's Historic Paper on Computability and the Turing Machine by Charles Petzold

I was translating a block of T-SQL code that calculated sexy primes into PostgreSQL and found out that in order to use variables, you need to wrap it into a function in PostgreSQL . I also found out that PostgreSQL up until version 11 didn't really have stored procedures either but you could have functions behave like procs

This Week I Tweeted

Hackers wipe US servers of email provider VFEmail

"At this time, the attacker has formatted all the disks on every server," the company said yesterday. "Every VM is lost. Every file server is lost, every backup server is lost."

"This was more than a multi-password via SSH exploit, and there was no ransom. Just attack and destroy," VFEmail said.

Yep someone got pissed of for something and this was a big F U operation


500px Hacked: Personal Data Exposed for All 14.8 Million Users

The popular photo-sharing service 500px has announced that it was the victim of a hack back in 2018 and that personal data was exposed for all the roughly 14.8 million accounts that existed at the time.

In an email sent out to users and an announcement posted to its website, 500px states that it was only on February 8th, 2019, that its team learned of an unauthorized intrusion to its system that occurred on or around July 5th, 2018.

The personal data that may have been stolen by the intruder includes first and last names, usernames, email addresses, password hashes (i.e. not plaintext passwords), location (i.e. city, state, country), birth date, and gender.

Took over 6 months to find out...  that is a very long time.. as always make sure that your password is unique for each site that you use



Google will spend $13 billion on U.S. real estate in 2019, expanding into Nevada, Ohio  and Texas

CEO Sundar Pichai said in a blog post on Wednesday that the company is building new data centers and offices and expanding several key locations across the U.S., spending $13 billion this year.

Pichai outlined the plans, which include opening new data centers in Nevada, Ohio, Texas and Nebraska, the first time the company will have infrastructure locations in those states. The company is also doubling its workforce in Virginia, providing greater access to Washington, D.C., with a new office and more data center space, and expanding its New York campus at Hudson Square.

Have to spend all that that money to catch up to Amazon and Microsoft in the cloud



Red Hat Satellite to standardize on PostgreSQL backend, will be dropping MongoDB

When will MongoDB Community Edition be dropped as an embedded database within Red Hat Satellite?
This database change is a still to come, but the product team wanted to go ahead and communicate this intent to our users so they were not caught by surprise as this is a change to the underlying databases of Satellite.  No specific timing or release is being communicated at this time. At this point we’re simply hoping to raise awareness of the change that is coming to help users of Satellite prepare for the removal of MongoDB.


This is in response to the license changes that MongoDB made recently... Looking at the chart below..it looks like this is no worry to investors, MongoDB  just hit a all time high

RIP Bruno Ganz, who Gen X remembers as the angel in "Wings of Desire" and millennials remember as Hitler in that bunker scene.

You have seen all the parodies of course, I actually only watched this movie on January 6th 2018. Downfall is an excellent movie, if you have some time, make sure to watch it


 

Some cool stuff you might enjoy

Using SonarQube, SonarQube Scanner and the sonar-tsql-plugin to run static code analysis  

I wrote this post for a friend so that he has a reference on how to install SonarQUbe and how to get started. This post explain how you can user SonarQube to run static code analysis against your T-SQL procs and functions

February release of @AzureDataStudio is now available! 

- Admin Pack for SQL Server extension
- Auto-sizing columns in results
- Notebook UI improvements
- Profiler Filtering
- Save Results as XML
- Deploy scripts

I am still using SSMS but maybe I will switch to DataStudio one of these days


Someone took 50,000 images of the night sky to make an 81 Megapixel image of the moon  It's beautiful 
See it here: https://www.reddit.com/r/space/comments/arer0k/i_took_nearly_50000_images_of_the_night_sky_to/ … 

mirrors of both JPG and PNG in zoomable versions here:

https://micr.io/i/clIZW  (JPG)
https://micr.io/i/WFjqr  (PNG)

Finding rows where the column starts or ends with a 'bad' character  

Another post I wrote because of a problem that a co-worker had with some data


A nice view while going to the Princeton Junction train station...  had to take a pic