Installation Environment Vmware Workstation pro It is recommended to use the snapshot to store the state of each installation stage to avoid installation failures and causing the installation to start from scratch. Ubuntu 22.04 windows 11 Hardware settings create 3 VM: 4 cores and 4G memory and 100G capacity Before installing K8s (All use the root user) set host: 192.168.47.135 master 192.168.47.131 node1 192.168.47.132 node2 set root ssh connection: sudo su - echo "PermitRootLogin yes" >> /etc/ssh/sshd_config systemctl restart sshd sudo passwd ssh-keygen for i in {master,node1,node2}; do ssh-copy-id root@$i; done set Ipvs and conf create conf file: for i in {master,node1,node2}; do ssh root@$i 'cat << EOF > /etc/modules-load.d/containerd.conf overlay br_netfilter EOF'; done execute conf: for i in {master,node1,node2}; do ssh root@$i 'modprobe overlay;modprobe br_netfilter;'; done create 99-kubernetes-cri.conf file: for i in {maste...
Consistency is essential for transactions between distributed systems and individual systems.
Some concepts will be discussed here.
ACID
- Atomicity:
- Atomicity guarantees that each transaction is treated as a single "unit", which either succeeds completely or fails completely.
- Consistency:
- Consistency ensures that a transaction can only bring the database from one consistent state to another, preserving database invariants: any data written to the database must be valid according to all defined rules, including constraints, cascades, triggers, and any combination thereof.
- Isolation:
- Isolation ensures that the concurrent execution of transactions leaves the database in the same state that would have been obtained if the transactions were executed sequentially.
- Durability:
- Durability guarantees that once a transaction has been committed, it will remain committed even in the case of a system failure (e.g., a power outage or crash).
Isolation Levels
- Read Uncommitted:
- There is not much isolation between transactions at all, i.e., no locks. Transactions can see changes made by other transactions to data that has not been committed.
- Read Committed:
- The phenomenon of dirty reading is avoided because any uncommitted changes are not visible to any other transaction until the change is committed.
- Repeatable Read:
- This isolation level returns the same result set throughout the transaction execution for the same Select run any number of times during the progression of a transaction.
- This is how it works, a snapshot of the Select is taken the first time the Select is run during the transaction and the same snapshot is used throughout the transaction when the same Select is executed.
- Serializable:
- Serializable completely isolates the effect of one transaction from others.
- It is similar to Repeatable isolation with the additional restriction that the row selected by one transaction cannot be changed by another until the first transaction finishes.
CAP
- Consistency:
- Every read receives the most recent write or an error.
- Availability:
- Every request receives a (non-error) response, without the guarantee that it contains the most recent write.
- Partition tolerance:
- The system continues to operate despite an arbitrary number of messages being dropped (or delayed) by the network between nodes.
2PC
- It is a distributed algorithm that coordinates all the processes that participate in a distributed atomic transaction on whether to commit or abort (roll back) the transaction.
- This protocol (a specialized type of consensus protocol) achieves its goal even in many cases of temporary system failure (involving either process, network node, communication, etc. failures), and is thus widely used.
3PC
- In computer networking and databases, the three-phase commit protocol (3PC)[1] is a distributed algorithm that lets all nodes in a distributed system agree to commit a transaction. It is a more failure-resilient refinement of the two-phase commit protocol (2PC).
- A two-phase commit protocol cannot dependably recover from a failure of both the coordinator and a cohort member during the Commit phase. The three-phase commit protocol eliminates this problem by introducing the Prepared to commit state. If the coordinator fails before sending preCommit messages, the cohort will unanimously agree that the operation was aborted
XA
- XA transactions are designed to allow distributed transactions, where a transaction manager (the application) controls a transaction that involves multiple resources.
- Such resources are usually DBMSs, but could be resources of any type. The whole set of required transactional operations is called a global transaction.
- XA used a 2-phases commit (2PC).
SAGA
Saga is a sequence of local transactions. Each local transaction updates the database and publishes a message or event to trigger the next local transaction in the saga. If a local transaction fails because it violates a business rule then the saga executes a series of compensating transactions that undo the changes that were made by the preceding local transactions.
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