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System Programming
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Kernel and system programming is the process of creating the software necessary for a computer or device to function and operate other programs. Some operating systems (such as Microsoft Windows) are proprietary, but others, such as the various Linux distributions, are open source.
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I've got a job creating the backend for a mobile app for a company. They will need me to do sysadmin tasks as well.
This app is useless if it can't connect to a server. I need to come up with a redundant setup, ideally over different providers (would like to use Linode and AWS).
I was wondering - what is this called, and how do I set it up? The most similar thing I have done is hosting a database on a separate server - both of those were in the same datacenter. I've read that you do not want the database to accept connections from public IP Addresses.
How do I set this up where there is redundancy over multiple data centers?
This app is useless if it can't connect to a server. I need to come up with a redundant setup, ideally over different providers (would like to use Linode and AWS).
I was wondering - what is this called, and how do I set it up? The most similar thing I have done is hosting a database on a separate server - both of those were in the same datacenter. I've read that you do not want the database to accept connections from public IP Addresses.
How do I set this up where there is redundancy over multiple data centers?
Constructors are not inherited:
The sub class cannot inherit constructors from its super class. Consider the following example:
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public class Super {
protected String text;
public Super(String text) {
this.text = text;
}
}
public class Sub extends Super {
}
We can create a new instance of Super like this:
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Super super = new Super(“Hello”); //OK
But we cannot do the same for the Sub class:
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Sub sub = new Sub(“Hello”); //Compile error, since constructor is not inherited
The solution is to write a constructor for the sub class and call the super’s constructor, for example:
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public class Sub extends Super {
public Sub(String text) {
super(text);
}
}
https://www.codejava.net/java-core/the-java-language/12-rules-and-examples-about-inheritance-in-java
i wrote as below
package SuperSub;
public class Super {
protected String text;
public Super(String text) {
this.text = text;
}
}
package SuperSub;
public class Sub extends Super {
//Super super = new Super(“Hello”);
}
i am getting error in line 2 of Sub class
Implicit super constructor Super() is undefined for default constructor. Must define an explicit constructor
package SuperSub;
public class Sub extends Super {
public Sub(String text) {
super(text);
// TODO Auto-generated constructor stub
}
//Super super = new Super(“Hello”);
}
Please advise
package SuperThis;
public class Sub extends Super {
/*public static void main(String[] args) {
super.bar();
this.bar();
}*/
public void bar() {
System.out.println("Sub.bar()...");
}
public void test() {
super.bar();
this.bar();
}
// Sub sub=new Sub();
// sub.test();
this.test();
}
i see error as below at line 21,15
Syntax error, insert "}" to complete ClassBody
Please advise
The super keyword:
In Java, the superkeyword is used to access members of the super type from the sub type. For example:
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public class Super {
protected void bar() {
System.out.println("Super.bar()...");
}
}
public class Sub extends Super {
public void bar() {
System.out.println("Sub.bar()...");
}
public void test() {
super.bar();
this.bar();
}
}
Here, we can see that both classes have a method called bar() (overriding). Therefore, if we want to invoke the super’s version of the bar() method, the super keyword is used.
super with this example not working for me
package SuperThis;
public class Sub extends Super {
public static void main(String[] args) {
super.bar();
this.bar();
}
public void bar() {
System.out.println("Sub.bar()...");
}
//public void test() {
// super.bar();
//this.bar();
// }
}
above code giving below error
Cannot use super in a static context
Cannot use this in a static context
how to fix this
package SuperThis;
public class Test {
public static void main(String[] args) {
Sub sub=new Sub();
sub.test();
}
}
Super.bar()...
Sub.bar()...
does it need separate class for this to test
package SuperThis;
public class Sub extends Super {
/*public static void main(String[] args) {
super.bar();
this.bar();
}*/
public void bar() {
System.out.println("Sub.bar()...");
}
public void test() {
super.bar();
this.bar();
}
// Sub sub=new Sub();
// sub.test();
test();
}
above gives error at line 20
Multiple markers at this line
- This method requires a body instead of a
semicolon
- Return type for the method is missing
- Duplicate method test() in type Sub
please advise
Remember that Java does not allow a class inherits two or more classes directly. To understand why multiple inheritance is not allowed, consider the following example:
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public class A {
public void methodA() {
}
public void foo() {
}
}
public class B {
public void methodB() {
}
public void foo() {
}
}
Suppose that we want to write a class C that extends both A and B like this:
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public class C extends A, B {
public void methodC() {
foo();
}
}
As you can see, both A and B has a method called foo(), so which foo() method the class C invokes exactly? from A or B? This case is ambiguous hence Java does not allow.
https://www.codejava.net/java-core/the-java-language/12-rules-and-examples-about-inheritance-in-java
i tried as below
package MultipleInheritance;
public class A {
public void methodA() {
}
public void foo() {
}
}
package MultipleInheritance;
public class B {
public void methodB() {
}
public void foo() {
}
}
package MultipleInheritance;
public class C extends A, B {
public void methodC() {
foo();
}
}
on C class i get below error
Multiple markers at this line
- Syntax error on token "extends", delete this token
- Syntax error, insert "ClassBody" to complete
ClassDeclaration
- Syntax error, insert "}" to complete Block
can you please advise what above error means
it did not say "multiple inheritance of state not allowed"
Please advise
6. Multiple inheritance of state is not allowed:
Remember that Java does not allow a class inherits two or more classes directly. To understand why multiple inheritance is not allowed, consider the following example:
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public class A {
public void methodA() {
}
public void foo() {
}
}
public class B {
public void methodB() {
}
public void foo() {
}
}
Suppose that we want to write a class C that extends both A and B like this:
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public class C extends A, B {
public void methodC() {
foo();
}
}
As you can see, both A and B has a method called foo(), so which foo() method the class C invokes exactly? from A or B? This case is ambiguous hence Java does not allow.
7. Multiple inheritance of type is allowed:
This means Java does allow multiple inheritance between interfaces. For example:
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public interface X {
public void methodX();
}
public interface Y {
public void methodY();
}
public interface Z extends X, Y {
public void methodZ();
}
This is allowed because interfaces do not have concrete methods, thus there is no ambiguity.
Likewise, we can have a class implements multiple interfaces:
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public class Sub implements X, Y, Z {
public void methodX() { }
public void methodY() { }
public void methodZ() { }
}
if both Interface X and Interface Y has same method called methodAB what happens?
Let’s look at the constructor of the Truckclass - it can access the protected field numberOfWheels and the default field name. However, it cannot access the private field age. We can write:
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Truck truck = new Truck();
truck.start();
truck.move();
But the Java compiler will complain if we try to invoke the private method test():
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truck.test(); // COMPILE ERROR, since private member is not inherited
https://www.codejava.net/java-core/the-java-language/12-rules-and-examples-about-inheritance-in-java
i supposed to put below code in which class Car or Truck or Moveable?
public class Truck extends Car {
public Truck() {
numberOfWheels = 8;
name = "Truck";
age=10;
}
Truck truck = new Truck();
truck.start();
truck.move();
}
or as below
public class Car extends Vehicle {
String name;
protected int age;
//protected int age;
protected int numberOfWheels = 4;
public void move() {
System.out.print("Moving by engine...");
}
@Override
public void start() {
// TODO Auto-generated method stub
}
@Override
public void stop() {
// TODO Auto-generated method stub
}
/*Truck truck = new Truck();
truck.start();
truck.move();*/
}
below i cannot put as it is interface
public interface Moveable {
public void start();
public void stop();
public void move();
}
please advise
Don’t use a for loop with an index (or counter) variable if you can replace it with the enhanced for loop (since Java 5) or forEach (since Java 8). It’s because the index variable is error-prone, as we may alter it incidentally in the loop’s body, or we may starts the index from 1 instead of 0.
Consider the following example that iterates over an array of Strings:
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String[] names = {"Alice", "Bob", "Carol", "David", "Eric", "Frank"};
for (int i = 0; i < names.length; i++) {
doSomething(names[i]);
}
As you can see, the index variable i in this for loop can be altered incidentally which may cause unexpected result. We can avoid potential problems by using an enhanced for loop like this:
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for (String aName : names) {
doSomething(aName);
}
This does not only remove potential issues but also make the code cleaner and more succinct.
how is it possible to do for loop index modifycation?
how enhanced for loop is diferent from for each loop?
is there any case where we still has to use traditional for loop with index
please advise
public class CollectionsRef {
private HashSet<Integer> numbers;
public ArrayList<String> getList() {
return new ArrayList<String>();
}
public void setNumbers(HashSet<Integer> numbers) {
this.numbers = numbers;
}
}
Look at the reference types which are collection implementation classes - this locks the code to work with only these classes HashSet and ArrayList. What if we want the method getList() can return a LinkedList and the method setNumbers() can accept a TreeSet?
The above class can be improved by replace the class references to interface references like this:
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public class CollectionsRef {
private Set<Integer> numbers;
public List<String> getList() {
// can return any kind of List
[b] return new ArrayList<String>();[/b]
}
public void setNumbers(Set<Integer> numbers) {
// can accept any kind of Set
this.numbers = numbers;
}
}
can we have generic List as return type to provide more flexibility to future changes to collection implementation?
https://www.codejava.net/coding/10-java-core-best-practices-every-java-programmer-should-know
Please advise
Avoid Redundant Initialization (0-false-null)
It’s very unnecessary to initialize member variables to the following values: 0, false and null. Because these values are the default initialization values of member variables in Java. For example, the following initialization in declaration is unnecessary:
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public class Person {
private String name = null;
private int age = 0;
private boolean isGenius = false;
}
This is also redundant:
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public class Person {
private String name;
private int age;
private boolean;
public Person() {
String name = null;
int age = 0;
boolean isGenius = false;
}
}
Therefore, if you know the default initialization values of member variables, you will avoid unnecessary explicit initialization. See more here:
i am not clear on below
This is also redundant:
does it mean initialization in the constructor as well apart from at class level
public Person() {
String name = null;
int age = 0;
boolean isGenius = false;
}
}
https://www.codejava.net/coding/10-java-core-best-practices-every-java-programmer-should-know
Please advise
Exploring SQL Server 2016: Fundamentals
Learn the fundamentals of Microsoft SQL Server, a relational database management system that stores and retrieves data when requested by other software applications.
It’s a very bad idea to create an interface which is solely for declaring some constants without any methods. Here’s such an interface:
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public interface Color {
public static final int RED = 0xff0000;
public static final int BLACK = 0x000000;
public static final int WHITE = 0xffffff;
}
It’s because the purpose of interfaces is for inheritance and polymorphism, not for static stuffs like that. So the best practice recommends us to use an enum instead. For example:
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public enum Color {
BLACK, WHITE, RED
}
In case the color code does matter, we can update the enum like this:
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public enum Color {
BLACK(0x000000),
WHITE(0xffffff),
RED(0xff0000);
private int code;
Color(int code) {
this.code = code;
}
public int getCode() {
return this.code;
}
}
what is the meaning of color code does not matter and updating like below?
In case the color code does matter, we can update the enum like this:
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public enum Color {
BLACK(0x000000),
WHITE(0xffffff),
RED(0xff0000);
private int code;
Color(int code) {
this.code = code;
}
public int getCode() {
return this.code;
}
}
when we create special AppConstants class?
can there be interface just for constants?
please advise
String sql = "Insert Into Users (name, email, pass, address)";
sql += " values ('" + user.getName();
sql += "', '" + user.getEmail();
sql += "', '" + user.getPass();
sql += "', '" + user.getAddress();
sql += "')"[b][u];[/u][/b]
https://www.codejava.net/coding/10-java-core-best-practices-every-java-programmer-should-know
https://www.w3schools.com/sql/sql_insert.asp
same question i have with StringBuilder as well
StringBuilder sbSql
= new StringBuilder("Insert Into Users (name, email, pass, address)");
sbSql.append(" values ('").append(user.getName()
sbSql.append("', '").append(user.getEmail()
sbSql.append("', '").append(user.getPass())
sbSql.append("', '").append(user.getAddress
sbSql.append("')");
String sql = sbSql.toString();
why we need to do toString only in case of StringBuilder
also what it mean by String builder not thread safe and string buffere thread safe
any example or link to prove this theory into practical?
Please advise
Avoid Empty Catch Blocks
It’s a very bad habit to leave catch blocks empty, as when the exception is caught by the empty catch block, the program fails in silence, which makes debugging harder. Consider the following program which calculates sum of two numbers from command-line arguments:
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public class Sum {
public static void main(String[] args) {
int a = 0;
int b = 0;
try {
a = Integer.parseInt(args[0]);
b = Integer.parseInt(args[1]);
} catch (NumberFormatException ex) {
}
int sum = a + b;
System.out.println("Sum = " + sum);
}
}
Note that the catch block is empty. If we run this program by the following command line:
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java Sum 123 456y
It will fail silently:
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Sum = 123
when i tried above example i am getting different error as below istead of getting 123
public class Sum {
public static void main(String[] args) {
int a = 0;
int b = 0;
try {
a = Integer.parseInt(args[0]);
b = Integer.parseInt(args[1]);
} catch (NumberFormatException ex) {
}
int sum = a + b;
System.out.println("Sum = " + sum);
}
}
Exception in thread "main" java.lang.ArrayIndexOutOfB
at Sum.main(Sum.java:7)
https://www.codejava.net/coding/10-java-core-best-practices-every-java-programmer-should-know
even below good catch block example also gives same error
public class SumFixed {
public static void main(String[] args) {
int a = 0;
int b = 0;
try {
a = Integer.parseInt(args[0]);
b = Integer.parseInt(args[1]);
} catch (NumberFormatException ex) {
System.out.println("One of the arguments are not number." +
"Program exits.");
return;
}
int sum = a + b;
System.out.println("Sum = " + sum);
}
}
class Parent {
//Parent(){}
Parent(){}
Parent(int number) {
}
}
class Child extends Parent {
Child(int a, int b) {
}
}
for above code do not i need to give constructor as below with two arguments?
Parent(int a, int b){}
//if i give constructor like above does it still called default constructor?
what is the meaning of below sentence?
4. The default constructor is only generated by the compiler:https://www.codejava.net/java-core/the-java-language/9-rules-about-constructors-in-java
If we explicitly write a constructor that looks exactly the same as the default constructor, it is NOT called the default constructor.
Please advise
I am trying ssh into a remote server, capturing the process ID, and stopping the app using the process ID.
For some reason I am loosing the value of the variable PROCESS in the SSH session, all the logic works fine if i run it locally. Below is the code and the execution part where i am loosing the variable (PROCESS) Value. Can someone tell me why i am not able to capture the echo "$PROCESS" and $PROCESS below.
Stoptomcat()
{
. /apps/web/properties/tomca
for server in "${dev_host_Array[@]}"
do
echo "connecting to the server $server" | tee -a /tmp/tomcat-App-operation.
ssh -q "$server" bash -c "'
PROCESS=`ps -ef | grep $app_name | grep -v "grep" | grep -v "Tom.sh" | awk '{print $2}'`
echo "$PROCESS"
if [ ! -x $PROCESS ]; then
/apps/tomcat/$app_name/bin
pid=$!
declare -i elapsed=0
while ps -p ${pid} >/dev/null; do
sleep 1
if ((++elapsed % 60 == 0)); then
kill -9 $process
exit
fi
done
else
echo " TOMCAT $app_name is already in stopped state"
fi
'"
done
}
Execution:
+ for server in '"${dev_host_Array[@]}"'
+ tee -a /tmp/tomcat-App-operation.
+ echo 'connecting to the server testserver1'
connecting to the server testserver1
++ ps -ef
++ grep -v Tom.sh
++ awk '{print $2}'
++ grep …
For some reason I am loosing the value of the variable PROCESS in the SSH session, all the logic works fine if i run it locally. Below is the code and the execution part where i am loosing the variable (PROCESS) Value. Can someone tell me why i am not able to capture the echo "$PROCESS" and $PROCESS below.
Stoptomcat()
{
. /apps/web/properties/tomca
for server in "${dev_host_Array[@]}"
do
echo "connecting to the server $server" | tee -a /tmp/tomcat-App-operation.
ssh -q "$server" bash -c "'
PROCESS=`ps -ef | grep $app_name | grep -v "grep" | grep -v "Tom.sh" | awk '{print $2}'`
echo "$PROCESS"
if [ ! -x $PROCESS ]; then
/apps/tomcat/$app_name/bin
pid=$!
declare -i elapsed=0
while ps -p ${pid} >/dev/null; do
sleep 1
if ((++elapsed % 60 == 0)); then
kill -9 $process
exit
fi
done
else
echo " TOMCAT $app_name is already in stopped state"
fi
'"
done
}
Execution:
+ for server in '"${dev_host_Array[@]}"'
+ tee -a /tmp/tomcat-App-operation.
+ echo 'connecting to the server testserver1'
connecting to the server testserver1
++ ps -ef
++ grep -v Tom.sh
++ awk '{print $2}'
++ grep …
Hi Experts,
I have this question after resolving the following
https://www.experts-exchange.com/questions/29109077/How-to-concatenate-all-files-from-one-folder-into-one-ignoring-headers.html#a42623555
How can I modify the command to
1- Ignore all headers
2- include only files created in specific date range
3- include only files with specific names, like "*PatSched* and "*PatChanges*"
Thanks in advance.
I have this question after resolving the following
https://www.experts-exchange.com/questions/29109077/How-to-concatenate-all-files-from-one-folder-into-one-ignoring-headers.html#a42623555
How can I modify the command to
1- Ignore all headers
2- include only files created in specific date range
3- include only files with specific names, like "*PatSched* and "*PatChanges*"
Thanks in advance.
What are the command can be used during debug windows memory dump to identify list of port and associated application. In normal windows we may use netstat -anob, but how to get to be execute in memory dump
I have to migrate the FS GPFS (3.4) on AIX server on new NSD disks, under the current configuration.
Which replication procedure is best to use?
[root@crmcas01]/tmp# mmlsconfig
Configuration data for cluster TEST:
--------------------------
myNodeConfigNumber 1
clusterName TEST
clusterId 13882357993337224079
autoload yes
minReleaseLevel 3.4.0.7
dmapiFileHandleSize 32
tiebreakerDisks tiebreaker01
worker1Threads 500
traceRecycle global
tracedevBufferSize 1048576
traceFileSize 300000000
trace all 4 tm 2 thread 1 mutex 1 vnode 5 ksvfs 2 klockl 2 io 3 pgalloc 1 mb 1 lock 2 fsck 3
pagepool 8G
nfsPrefetchStrategy 1
maxMBpS 2048
maxStatCache 256000
maxFilesToCache 64000
adminMode allToAll
File systems in cluster TEST:
--------------------------
/dev/SwReport
/dev/fsWBCp
/dev/fsCRMp
/dev/sbsiebCRMp
/dev/sbsiebgCRMp
Which replication procedure is best to use?
[root@crmcas01]/tmp# mmlsconfig
Configuration data for cluster TEST:
--------------------------
myNodeConfigNumber 1
clusterName TEST
clusterId 13882357993337224079
autoload yes
minReleaseLevel 3.4.0.7
dmapiFileHandleSize 32
tiebreakerDisks tiebreaker01
worker1Threads 500
traceRecycle global
tracedevBufferSize 1048576
traceFileSize 300000000
trace all 4 tm 2 thread 1 mutex 1 vnode 5 ksvfs 2 klockl 2 io 3 pgalloc 1 mb 1 lock 2 fsck 3
pagepool 8G
nfsPrefetchStrategy 1
maxMBpS 2048
maxStatCache 256000
maxFilesToCache 64000
adminMode allToAll
File systems in cluster TEST:
--------------------------
/dev/SwReport
/dev/fsWBCp
/dev/fsCRMp
/dev/sbsiebCRMp
/dev/sbsiebgCRMp
Hi Experts,
I have the following batch file
Would like to have for the second file (the access file), to zip it into the destination, instead of just copying.
How can I accomplish that?
fyi- I have windows 7.
Thanks in advance.
I have the following batch file
@echo off
setlocal
set tm=%time: =0%
set tm=%tm::=%
set dt=%date:~10,4%%date:~4,2%%date:~7,2%
copy C:\Users\bfuchs\Dropbox\Caspio\CaspioTables.zip h:\CaspioTablesDaily\CaspioTables%dt%%tm:~0,4%.zip
copy F:\Data\SkilledNursingVisitNotestbl.mdb h:\AccessTablesDaily\Skilled_Nursing_Tables%dt%%tm:~0,4%.mdb
Would like to have for the second file (the access file), to zip it into the destination, instead of just copying.
How can I accomplish that?
fyi- I have windows 7.
Thanks in advance.
Build an E-Commerce Site with Angular 5
Learn how to build an E-Commerce site with Angular 5, a JavaScript framework used by developers to build web, desktop, and mobile applications.
Hi Experts,
the print screen key stopped working on my pc.
any suggestion?
preferably something that does not require restarting my pc...
thanks in advance.
fyi- I'm connected remotely thru gotomypc, however pass special keys to host is checked off.
the print screen key stopped working on my pc.
any suggestion?
preferably something that does not require restarting my pc...
thanks in advance.
fyi- I'm connected remotely thru gotomypc, however pass special keys to host is checked off.
#Requires -version 3.0
$WarningPreference="Contin
#variables
$ScriptPath = $(Split-Path -Parent $MyInvocation.MyCommand.De
#Log Timestamp
$logdate=Get-Date -Format ddMMyyyy_HHmmss
$Logfile = "E:\Logs\FileProcessing_$l
function LogWrite ([string]$logstring)
{
Add-content $Logfile -value $logstring
}
#Zip Files and move to backup folder
$sourcefolder="E:\Data"
$backupFolder="E:\Data\Bac
I am want to build script which will do housekeeping of logs, archive folder and log activity if any file deleted then mention the file name deleted and similaly if log file deleted then log it what files deleted.
if no files to delete for day then mention in the log file no files to delete.
Backup folder archive data should have 7 years, more then 7 years should do rotation (older files to delete and new files to keep).
Backup folder 7 years files to keep, after that older archive files to delete and newer archive file to keep it.
Log folder 1 years logs to keep, after that older log files to delete and newer log file to keep it.
$WarningPreference="Contin
#variables
$ScriptPath = $(Split-Path -Parent $MyInvocation.MyCommand.De
#Log Timestamp
$logdate=Get-Date -Format ddMMyyyy_HHmmss
$Logfile = "E:\Logs\FileProcessing_$l
function LogWrite ([string]$logstring)
{
Add-content $Logfile -value $logstring
}
#Zip Files and move to backup folder
$sourcefolder="E:\Data"
$backupFolder="E:\Data\Bac
I am want to build script which will do housekeeping of logs, archive folder and log activity if any file deleted then mention the file name deleted and similaly if log file deleted then log it what files deleted.
if no files to delete for day then mention in the log file no files to delete.
Backup folder archive data should have 7 years, more then 7 years should do rotation (older files to delete and new files to keep).
Backup folder 7 years files to keep, after that older archive files to delete and newer archive file to keep it.
Log folder 1 years logs to keep, after that older log files to delete and newer log file to keep it.
Hi Experts,
I have the following function trying to synchronize my local folder with a FTP folder.
I have the following function trying to synchronize my local folder with a FTP folder.
Sub Example()
Dim mySession As New Session
' Enable custom error handling
On Error Resume Next
Download mySession
' Query for errors
If Err.Number <> 0 Then
MsgBox "Error: " & Err.Description
' Clear the error
Err.Clear
End If
' Disconnect, clean up
mySession.Dispose
' Restore default error handling
On Error GoTo 0
End Sub
Public Sub Download(ByRef mySession As Session)
'Public Sub Download()
' Setup session options
Dim mySessionOptions As New SessionOptions
With mySessionOptions
.Protocol = Protocol_Sftp
.hostname = "sftp.MySite.com"
.username = "MyUser"
.password = "MyPWD"
.SshHostKeyFingerprint = "ssh-rsa 2048 xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx"
End With
' Connect
mySession.Open mySessionOptions
' Upload files
Dim myTransferOptions As New TransferOptions
myTransferOptions.TransferMode = TransferMode_Binary
'myTransferOptions.ResumeSupport = TransferResumeSupportState.TransferResumeSupportState_Off
myTransferOptions.ResumeSupport.State = TransferResumeSupportState_Off
Dim transferResult As SynchronizationResult
'Set transferResult = _
mySession.GetFiles("/Outbox/*PatChanges*", "H:\FTP\", False, myTransferOptions)
what are differences between eclipse short cuts F3 and Control +Shift+G
when to use which one?
Please advise
when to use which one?
Please advise
Hi Experts,
I have the function below that downloads files from a FTP server.
I have the function below that downloads files from a FTP server.
Option Explicit
Sub Example()
Dim mySession As New Session
' Enable custom error handling
On Error Resume Next
Upload mySession
' Query for errors
If Err.Number <> 0 Then
MsgBox "Error: " & Err.Description
' Clear the error
Err.Clear
End If
' Disconnect, clean up
mySession.Dispose
' Restore default error handling
On Error GoTo 0
End Sub
Private Sub Download(ByRef mySession As Session)
' Setup session options
Dim mySessionOptions As New SessionOptions
With mySessionOptions
.Protocol = Protocol_Sftp
.HostName = "example.com"
.UserName = "user"
.Password = "mypassword"
.SshHostKeyFingerprint = "ssh-rsa 2048 xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx"
End With
' Connect
mySession.Open mySessionOptions
' Upload files
Dim myTransferOptions As New TransferOptions
myTransferOptions.TransferMode = TransferMode_Binary
Dim transferResult As TransferOperationResult
Set transferResult = _
mySession.GetFiles("/home/user/*", "H:\FTP\", False, myTransferOptions)
' Throw on any error
transferResult.Check
' Display results
Dim transfer As TransferEventArgs
For Each transfer In transferResult.Transfers
MsgBox "Download of " & transfer.Filename & "
Hi,
suppose i have a mysql table with rows (originalUrl : varchar(500) , shortUrl : varchar(10))
The queries that will be executed on this table will mostly be
1. select * from table where shortUrl = X
2. insert into table (originalUrl, shortUrl)
So there should be an index on shortUrl to speed this up.
I have the following question -
1. What exactly the index table will store ?
My understanding is index table will store items like - (shortUrl, pointerToDisk) // where pointerToDisk will locate exactly the place in disk where the row is stored.
2. Where is index table stored ?
Is it always stored in Disk or memory ?
3. What is the size of index table exceeds that of RAM ?
In this case the full index table will never be in RAM and so how will queries like select * from table where shortUrl = x execute
Will a part of index table be pulled out everytime to check the location ?
4. In case where this table is very huge say 3 TB. How big will index table be...
5. If index table is larger than size of RAM and since then the queries will take a lot of time. Is there a better alternative ?? Like using noSQL database. or storing data in two machines splitting them rather than on one machine ?
Thanks
suppose i have a mysql table with rows (originalUrl : varchar(500) , shortUrl : varchar(10))
The queries that will be executed on this table will mostly be
1. select * from table where shortUrl = X
2. insert into table (originalUrl, shortUrl)
So there should be an index on shortUrl to speed this up.
I have the following question -
1. What exactly the index table will store ?
My understanding is index table will store items like - (shortUrl, pointerToDisk) // where pointerToDisk will locate exactly the place in disk where the row is stored.
2. Where is index table stored ?
Is it always stored in Disk or memory ?
3. What is the size of index table exceeds that of RAM ?
In this case the full index table will never be in RAM and so how will queries like select * from table where shortUrl = x execute
Will a part of index table be pulled out everytime to check the location ?
4. In case where this table is very huge say 3 TB. How big will index table be...
5. If index table is larger than size of RAM and since then the queries will take a lot of time. Is there a better alternative ?? Like using noSQL database. or storing data in two machines splitting them rather than on one machine ?
Thanks
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