explain – How to trigger the Mysql parallel query function to start?

Please help, how to trigger the Mysql parallel query function to get started?
MySQL version is 8.0.19.

mysql> show variables like 'innodb_parallel_read_threads';
| Variable_name                | Value |
| innodb_parallel_read_threads | 4     |
1 row in set (0.00 sec)

Judging by the execution plan, although the cost value is high, it does not trigger parallel queries.

mysql> explain analyze SELECT count(a.name) FROM b,a WHERE b.id = a.id AND a.id < 10000G
*************************** 1. row ***************************
EXPLAIN: -> Aggregate: count(a.`name`)  (actual time=79199.970..79199.971 rows=1 loops=1)
    -> Inner hash join (b.id = a.id)  (cost=29804029261222.55 rows=29803521726988) (actual time=52129.791..79198.823 rows=9999 loops=1)
        -> Table scan on b  (cost=31.81 rows=18758239) (actual time=0.385..19630.712 rows=20000000 loops=1)
        -> Hash
            -> Filter: (a.id < 10000)  (cost=4909601.51 rows=15888229) (actual time=2.266..52117.583 rows=9999 loops=1)
                -> Table scan on a  (cost=4909601.51 rows=47669458) (actual time=2.262..48985.413 rows=50000000 loops=1)

1 row in set (1 min 19.25 sec)

Can anyone explain to me why Trump supporters see Democrats as a greater threat to democracy than Russia?

Because we have an army to defend our borders against Russia and MAD has maintained peace between us for decades.

– where while the Democrats are trying to destroy us from within by wanting to rewrite the document that created our Republic and pushing the same socialist policies that made the USSR and Venezuela sink into our throats.

– BUT it's not like Krushchev didn't warn us ….

"We cannot expect the Americans to move from capitalism to communism, but we can help their elected leaders to give the Americans small doses of socialism, until they suddenly wake up to find out that they have communism. "

functional programming – Can anyone explain the output of this code?

I recently had this question in my test to give the output of the following program. Although when I ran it in python, it gave a different output than I expected.

Source code:

def makenew(mystr):
    for i in mystr:
        if count%2!=0:
            if i.islower():
        print("The new string is:",newstr)


The new string is: Ss
The new string is: Ss1s
The new string is: Ss1s1s
The new string is: Ss1s1s1s
The new string is: Ss1s1s1s1s
The new string is: Ss1s1s1s1s1s
The new string is: Ss1s1s1s1s1s1s

I expected all of this to execute all of the characters in "mystr" and give an output where, when the number is even and lowercase, it would be added in uppercase and in the else part. And if the number was odd, it would add the number in str format.
Can anyone explain this outing?

terminology – How to explain the focal distance to someone who is not a photography lover?

Without going into the formulas, I think the easiest way to visually explain the focal length is to use an empty 35mm slide as a framing guide. (Note that over time, less and less people know what a 35mm film slide looks like, so the visual guide is less apt …)

First of all, you need to explain that focal length is a property of the lens. Just like a milk jug can hold 1 or 1/2 gallon or 1 liter, or a certain bottle of water can hold 1/2 liter, so any particular lens has a particular focal length. (In this analogy, zoom lenses are like collapsible water bottles, which have a certain minimum volume when folded down and a maximum volume when folded down). Just like volume is a property of this particular bottle, the focal length is therefore a property of this particular lens.

(Note: I didn't have to use a bottle volume for analogy. I could have used the height of the bottle as easily as the property. It doesn’t matter – it’s just an analogy)

Extending the analogy, it doesn't matter if the bottle is full, half full or empty – the capacity of the bottle is fixed. Just like with a lens: it doesn't matter if it's focused far or near – the focal distance of the lens is unchanged.

Related: What is the focal length and how does it affect my photos?

Now back to the cameras. Different focal lenses modify field of view when mounted on a certain camera. Conversely, when mounting different cameras (with different film or sensor sizes) on a particular lens, the field of vision is also affected.

Here is where the 35mm slide comes in when explaining to people: for a lens with a focal length ƒ (say, 50mm), if it was mounted on a film camera 35 mm (those that most people using film cameras know), then you will get the same field of vision just as you hold a 35mm film slide at a distance of ƒ (50mm, or about 2 inches, in this case) in front of your eye.

Another example: early in the evening of a full moon night, when the moon is low on the horizon and it looks impressive, if you want to capture it in full glory, imagine holding a empty 35 mm slide at arm's length (about 3 feet or or about 900 mm) to frame the moon. When framed with a slide holder at this distance, the moon will fill about 1/3 the height of the frame. So that gives you an idea of ​​the viewing angle of a 900mm lens on a 35mm film camera (or a 35mm full frame DSLR).

Related: What Focal Length Lens Do I Need To Photograph The Moon?

Now if you are talking about a camera with a smaller sensor, such as a 1.5 or 1.6 APS-C crop sensor on entry level DSLRs and mid-range, a 35mm film slide holder no longer works. The framing tool should be 1.5 times smaller. In this case, it would be 24 x 16 mm. Using the smaller "1.5 APS-C slider holder" as a framing guide, you can place it at the focal distance of the lens ƒ from your eye to judge the size of the field of view .

Related: Does My Crop Sensor Camera Really Turn My Lenses Into A Longer Focal Length?

This is the simplest way I have found to explain and visualize the focal distance, without delving into math with the formula of the thin lens and the formula of the angle pinhole vision.

numerical value – Explain the floor difference[Log[10., 1000]]and floor[Log[10, 1000]]

I have performed the following function:

Floor[Log[10., 1000]]

I expected this result:


but the result was


Then I deleted the decimal point and executed:

Floor [log [10, 1000]]

Floor[Log[10, 1000]]

with result:


as expected.

What is the explanation for this difference?

dependencies – Understanding how to interpret / explain the y axis in a partial dependence plot in R using pdp and XGBOOST

I used the xgboost package to create a gradient boosted model, similar to the y-axis interpretation questioner of partial dependence plots produced by the pdp package, to predict an event very low probability.

My model (surprisingly) has decent predictive value and now I'm interested in understanding and explaining the direction of influence of each of the predictor variables. Using the pdp package, I generated a series of partial dependency graphs, which I think illustrate the marginal effect of the predictor variable on the independent variable over a range of values.

With my limited knowledge, I can generally articulate what the intrigues show. (An example is pasted here: enter description of image here

In this case, the increase in travel time makes the event more likely up to about 30 minutes when the trend reverses. Beyond a 30-minute journey, the probability of the event decreases.

Even after reading the documentation and the thumbnails, I'm still not sure I understand exactly what the y-axis captures. What exactly are the values? What does "yhat" mean? I guess it means a predicted value of y. And why are all values ​​negative? Is it because for each given observation, the probability of the extremely rare event is very low?

Is there any point in trying to explain anything to a Democrat?

There is no point in trying to explain things to a Trump supporter.

They will always think that Trump is a great man, no matter what you say. Tell them the classified information that Trump has leaked that he shouldn't have, all the money that Trump has stolen from charities and the military, all the delayed stuff that he has said (the mills cause cancer, Paris is in Germany, etc.), all the outrageous evil all that he said, and all the other bad things he did, they will say "But Obama !! " or "But Hillary !!"

Which appropriate sentence to explain the item cannot be deleted?

I want to tell the user that this item cannot be deleted as it is the only item left in the list.

Liberals, explain why you kill human babies to improve the taste of pepsi?

Why you and your pro-life radicals aren't just adopting the more than 500,000 young people and children who "float" in DHS / Foster care, roll up your sleeves and offer a family to those who don't 39; don't have one ???? ?? Ohhhhhh, that would take a lifetime commitment, we don't want us to do it ?? We just want to post garbage on Pepsi, that’s the easy way, no engagement, just nonsense, nice and easy messages right?

What are the benchmarks in SEO?

Explain the referring domains in SEO?

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