Today we continue to review the mechanics of Active Directory replication:
We are referring to intrasite replication for the most often use cases of Active directory domain name-context item changes. Such AD replication takes place between DCs in pull operations, not pushes. AD controls and manages the transmission of AD Data with replication metadata. We saw that this metadata included
1) USN which revisions changes on local machine
2) HWMV which informs whether it is originating or replicating
3) UTDV which prevents repeated processing of replicating changes and helps with propagation dampening
The replicated change therefore includes the following:
the GUID of the DC that is replicating the change
the USN from the DC that is replicating the change
the GUID of the DC that originated the change
the USN from the DC that originated the change
Based on the UTDV table, the DC determines whether it needs to make the change or simply update the HWMV entry.
The DC also has to perform conflict resolution. There are three types of conflict that can occur in Active Directory environment, each of which uses a different method of conflict resolution.
1) The same object is updated in two originating servers
2) name collision when two objects are created by the same name
3) If one object is created but another deletes the container.
To; address first two types of conflict, the replication metadata includes two things - a version ID for the attribute and a timestamp. The third type of conflict is managed by moving to a specially designated container called the orphaned container.
We were comparing the Active directory replication to a database replication and suggesting that the snapshot isolation method works very well in this regard. Just like databases can be distributed with namespace and versions, we have similar comparison with active directory.
Generally a database detects conflicts in one of the following ways:
1) current versus old : the receiving site detects an update conflict if there is any difference between the old values of the replicated row and the current values of the same row at the receiving site
2) dulpicate : the receiving site detects a uniqueness conflict if a uniqueness constraint violation occurs during an insert or an update of the replicated data
3) missing : the receiving site detects a delete conflict if it cannot find a row for an update or delete statement because the primary key of the row does not exist.
Question can the usn, hwmv and utdv be simplified : hint : think globally unique version numbers, timestamps, action name and idempotent operations.
Courtesy : Laura Hunter, Windows Server Administration
#codingexercise
Convert an infix expression to postfix expression
An infix expression is like this a + b*c + d
An postfix expression is like this abc*d++
Operators have standard precedence
As we can see we are moving the operator, consequently a stack comes in useful.
The method proceeds like this
For every operand, maintain its sequence in the result
For every ( push it on the stack
For every ) pop elements from stack till matching open ( arrives or invalidate. the popped elements are added to resulting expression.
For every operator, empty the stack onto the result until the topmost of the stack has higher precedence than the current operator and then include the operator in the resulting expression.
That's it. since we only add operators to the stack, the sequence of operands is maintained
The opening and closing paranthesis are not included in the resulting expression because the operators are stacked and two operands apply the operation following it.
For example,
(a*b)^c => ab*c^
a*(b^c) => abc^*
We are referring to intrasite replication for the most often use cases of Active directory domain name-context item changes. Such AD replication takes place between DCs in pull operations, not pushes. AD controls and manages the transmission of AD Data with replication metadata. We saw that this metadata included
1) USN which revisions changes on local machine
2) HWMV which informs whether it is originating or replicating
3) UTDV which prevents repeated processing of replicating changes and helps with propagation dampening
The replicated change therefore includes the following:
the GUID of the DC that is replicating the change
the USN from the DC that is replicating the change
the GUID of the DC that originated the change
the USN from the DC that originated the change
Based on the UTDV table, the DC determines whether it needs to make the change or simply update the HWMV entry.
The DC also has to perform conflict resolution. There are three types of conflict that can occur in Active Directory environment, each of which uses a different method of conflict resolution.
1) The same object is updated in two originating servers
2) name collision when two objects are created by the same name
3) If one object is created but another deletes the container.
To; address first two types of conflict, the replication metadata includes two things - a version ID for the attribute and a timestamp. The third type of conflict is managed by moving to a specially designated container called the orphaned container.
We were comparing the Active directory replication to a database replication and suggesting that the snapshot isolation method works very well in this regard. Just like databases can be distributed with namespace and versions, we have similar comparison with active directory.
Generally a database detects conflicts in one of the following ways:
1) current versus old : the receiving site detects an update conflict if there is any difference between the old values of the replicated row and the current values of the same row at the receiving site
2) dulpicate : the receiving site detects a uniqueness conflict if a uniqueness constraint violation occurs during an insert or an update of the replicated data
3) missing : the receiving site detects a delete conflict if it cannot find a row for an update or delete statement because the primary key of the row does not exist.
Question can the usn, hwmv and utdv be simplified : hint : think globally unique version numbers, timestamps, action name and idempotent operations.
Courtesy : Laura Hunter, Windows Server Administration
#codingexercise
Convert an infix expression to postfix expression
An infix expression is like this a + b*c + d
An postfix expression is like this abc*d++
Operators have standard precedence
As we can see we are moving the operator, consequently a stack comes in useful.
The method proceeds like this
For every operand, maintain its sequence in the result
For every ( push it on the stack
For every ) pop elements from stack till matching open ( arrives or invalidate. the popped elements are added to resulting expression.
For every operator, empty the stack onto the result until the topmost of the stack has higher precedence than the current operator and then include the operator in the resulting expression.
That's it. since we only add operators to the stack, the sequence of operands is maintained
The opening and closing paranthesis are not included in the resulting expression because the operators are stacked and two operands apply the operation following it.
For example,
(a*b)^c => ab*c^
a*(b^c) => abc^*
No comments:
Post a Comment