When using Priority Preemptive Scheduling, does a higher priority yield way to a process with a lower priority but with a shorter burst time?
For example, if I had:
Arrival Time Burst Time Priority
P1 0 5 3
P2 2 6 1
P3 3 3 2
Would the Gannt chart look like this?
| P1 | P2 | P3 | P1 |
0 2 8 11 16
Priority Scheduling always selects the process(es) with the highest priority currently ready to run. If there is more than one process having the currently highest priority, you need a second scheduling algorithm to choose among these processes. Non-preemptive Priority Scheduling only selects a new process to run if the running process finished its work or yields (voluntarily) to the scheduler.
Preemptive Priority Scheduling is the same algorithm but if a new process having a higher priority than the currently running process arrives, it gets selected immediately. The new process has not to wait until the currently running process finishes or yields.
In your sample, the Gantt chart for Preemptive Priority Scheduling and 3 being the highest and 1 the lowest priority would look like:
| P1 | P3 | P2 |
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
| p1 | p2 | p3 | p1 |
0....2....8....11...14
taking 1 as the highest priority.
|p1 |p2 |p3 |p1 |
0 2 8 11 14
because preemptive approach will preempt if the priority of the newly-arrived process is higher than the priority of currently running process..
Related
I am currently trying to upskill myself within data analysis using tools such as SQL, EXCEL etc. So apologies, if what I am asking for may not make much sense, but happy to expand/clarify where required.
Problem :
I am trying to create a period by period line graph, showing pay across periods. However, with my current dataset the rows are :
employee codes and the columns are the individual periods with the values pertaining to that period for each row.
In order to achieve the requirements for my line graph. I would need to perform pivot of some sort to create a row per period for each worker. This will then allow me to group by periods for my line graph.
Current dataset :
Code Name Period 1 Period 2 Period 3
P1 Worker 1 2740.67 0 0
2 Worker 2 0 0 0
3 Worker 3 0 759.85 607.88
4 Worker 4 0 0 0
5 Worker 5 5000 5000 5000
6 Worker 6 1762.5 1672.5 960
12 Worker 7 6050 7750 5000
7 Worker 8 625.38 748.46 10
1234 Worker 9 2616.67 2616.67 2616.67
8 Worker 10 500 200 0
144 Worker 11 0 0 0
M100 Worker 12 423.08 0 0
M01 Worker 13 1583.33 1583.33 1583.33
M102 Worker 14 5833.33 5833.33 0
2403 Worker 15 8333.33 8333.33 11269.23
So for worker 5 they should have have 3 rows. The only thing i can think of is subqueries per worker that make up the columns or multiple unions, but seems rather time consuming ? Was hoping for a quicker efficient way of achieving what i need.
I've set up the Apache (2.4) load-balancer which is working okay. To monitor its performance, I enabled the balancer-manager handler, which shows the status of the balancers.
I noticed a "Load" column, which was not present in version 2.2, with a value that may be negative, but I don't understand its meaning nor I was able to find documentation relative to this.
Can anyone explain the meaning of that value or point me to the right documentation?
I now understood, how the calculation of "Load" works. Here is a I think more simpler example than on the apache documents page.
Let's say we have 3 worker and a configured load factor of 1.
1) Start
a | b | c
--+---+---
0 | 0 | 0
add the load factor of 1 to all workers
a | b | c
--+---+---
1 | 1 | 1
now select the one with highest value --> a and decrease by the sum of the factor of all (=3) - this is the selected worker
a | b | c
---+---+---
-2 | 1 | 1
2) next round, add again 1 to all
a | b | c
---+---+---
-1 | 2 | 2
now select the one with highest value --> b and decrease by the sum of the factor of all (=3) - this is the selected worker
a | b | c
---+----+----
-1 | -1 | 2
3) next round, add again 1
a | b | c
---+----+----
0 | 0 | 3
now select the one with highest value --> c and decrease by the sum of the factor of all (=3) - this is the selected worker
a | b | c
---+----+----
0 | 0 | 0
startover again :)
I hope this helps others.
The Load value is populated by lbstatus based on this line of code:
ap_rprintf(r, "<td>%d</td><td>", worker->s->lbstatus);
in https://svn.apache.org/viewvc/httpd/httpd/trunk/modules/proxy/mod_proxy_balancer.c?view=markup#l1767 (line might changed when the code modified)
Since your method is by request, lbstatus is specified by mod_lbmethod_byrequests which define:
lbstatus is how urgent this worker has to work to fulfill its quota of
work.
Details on the algorithm can be found here: https://httpd.apache.org/docs/2.4/mod/mod_lbmethod_byrequests.html
i too want to know to description for others column like BUSY, ELECTED etc.. my LB has BUSY over 100 already.. i though BUSY should not exceed 100 ( as in 100% server busyness or something )
I have event data from an app that helps tell me what people are doing inside my app.
userID|timestamp |name | value |
A | 1 |Launch | 23 |
A | 3 |ClickButton| Header|
B | 2 |Launch | 10 |
B | 5 |ClickBanner| ad |
etc
I am defining a Session as anytime someone has been out of the app for more than 5 minutes, the next entry is a new session. So if you come back in after 4 minutes, it is still the same session.
I use a lag to select the previous launch timestamp, add the value of time in seconds for that and then take the difference for the next launch. So I can select the first timestamp for each 'Session'
Now I need to map each non Launch event back to the session it is a part of so I can easily analyze things such as 'What percent of sessions include an ad click?'
I'm pulling my data using HIVE and am not having success finding an efficient way to do this as my dataset is fairly large.
Given the following table for calculating and average waiting time for the processes for priority based preemptive scheduling.
Process Burst Time Priority
P1 10 3
P2 1 1
P3 2 4
P4 1 5
P5 5 2
The gantt chart would be as follows:
| P2 | P5 | P1 | P3 | P4 |
0 1 6 16 18 19
I have following questions:
1) Is the turn around time = 19 units?
2) How do i calculate average waiting time? Is there a formula?
3) What if few processes have the same priority?
I am new to OS. I have viewed some other similar questions but I did not get exactly how to do it.
Given the data,before you have to implement priority based preemptive scheduling, you should know the following facts :-
priorities are usually numeric over a range
high numbers may indicate low priority (system dependent)
associate a priority with each process, allocate the CPU to the process with the highest priority
any 2 processes with the same priority are handled FCFS
Proceeding with this much of knowledge,the required Gantt chart would be the same as what you've drawn:-
| P2 | P5 | P1 | P3 | P4 |
0 1 6 16 18 19
1) Is the turn around time = 19 units?
No, the turnaround time will be 16 + 1 + 18 + 19 + 6 = 60.
Average turnaround time = 60 / 5 = 12.
2) How do i calculate average waiting time? Is there a formula?
Average waiting time is defined as the sum of total time waited before starting of the processes divided by the total number of processes.
Here, average waiting time = (6 + 0 + 16 + 18 + 1) / 5 = 41 / 5 = 8.2.
3) What if few processes have the same priority?
If the few processes will have same priority then the scheduling would be handled using First-Come First-Serve (FCFS) as mentioned in the 4th point above. So, everywhere including Gantt chart, the process coming first will be scheduled first and the other similar-priority process would be scheduled late as it came arrived late.
I hope it is crystal clear from my steps and doesn't need any further explanation.
Hello I have doubt regarding how to create the table for the pairwise testing.
For example if I have three parameter which can each attain two different values. How do I create a table of input with all possible combination then? Would it look something like this?
| 1 2 3
-----------
1 | 1 1 1
2 | 1 2 2
3 | 1 1 2
4 | 1 2 1
Does each parameter corresponds to each column?
However since I have 3 parameter, which each can take 2 different value. The number of test cases should be 2^3 isn't it?
There's a good article with links to some useful tools here:
http://blog.josephwilk.net/ruby/pairwise-testing-with-cucumber.html
For the parameters: each column is a parameter, and each row is a possible combination. Here is the table:
| 1 2 3
-----------
1 | 1 1 1
2 | 2 1 1
3 | 1 2 1
4 | 1 1 2
5 | 2 2 1
6 | 2 1 2
7 | 1 2 2
8 | 2 2 2
so 2^3=8 possible combinations as you can see :)
For the values: each column is a value, and each row is a possible combination:
| 1 2
--------
1 | 1 1
2 | 2 1
3 | 1 2
4 | 2 2
They are 2^2=4 possible combinations. Hope it helps.
1) Please note that pair-wise testing is not about scanning exhaustively all possible combination of values of all parameters. Firstly, such a scanning would give you an enormous amount of test cases that almost no existing system could be able to run all of them.
Secondly, pair-wise testing for a software system is based on the hope that the two parameters having the highest number of possible values are the culprit for the highest percentage of faults of that system.
This is of course only a hope and almost no rigorous scientific research has existed so far to prove that.
2) What I often see in the documentations discussing pair wise testing, like this is that the list of all possible values (aka the pair-wise test table) is not constructed in a well thought way. This creates confusions.
In your case, all the parameters have the same number of possible values (2 values), therefore you could choose any two parameters of those three to build the table. What you could pay attention is the ordering of the combination: you iterate first the top-right parameter, then the next parameter to the left, and so on, ...
Say if you have two parameters p1 and p2, p1 has two possible values apple and orange; and p2 has two possible values red and blue, then your pair-wise test table would be:
index| p1 p2
------------------
1 | apple red
2 | apple blue
3 | orange red
4 | orange blue