https://padlet.com/klehal1/ihrh13u6zjpcvem9 en-us 2023-09-28 08:35:40 UTC 2023-09-28 09:11:19 UTC hello@padlet.com klehal1 https://padlet.com/klehal1/ihrh13u6zjpcvem9/wish/2724306405 The consistency of the database is maintained because only one copy of data is held rather than 1 at each workstation

Expensive - powerful computer/server - available for many users

Access rights and security can be managed centrally

backup and recover can also be managed centrally]]> 2023-09-28 08:38:41 UTC https://padlet.com/klehal1/ihrh13u6zjpcvem9/wish/2724306405 klehal1 https://padlet.com/klehal1/ihrh13u6zjpcvem9/wish/2724311066 Records are copied locally to machine allowing user to edit on client side
Edited copy is then send back to central server]]> 2023-09-28 08:42:34 UTC https://padlet.com/klehal1/ihrh13u6zjpcvem9/wish/2724311066 klehal1 https://padlet.com/klehal1/ihrh13u6zjpcvem9/wish/2724319973 A record is locked when a client retrieves the data from it - this locks anyone else out from attempting to retrieve it

This solves the issue of multiple people changing one record at once

ISSUE
If two users are changing two separate records that are linked neither user could change the record and a DEADLOCK is reached.

Solved by serialisation

]]> 2023-09-28 08:49:26 UTC https://padlet.com/klehal1/ihrh13u6zjpcvem9/wish/2724319973 klehal1 https://padlet.com/klehal1/ihrh13u6zjpcvem9/wish/2724322886 This is a technique which ensure that transactions do not overlap in time - cannot interfere with each other or lead to updates being lost. A transaction cannot start until the previous one has finished 

implemented using time stamp ordering or commitment ordering]]> 2023-09-28 08:51:28 UTC https://padlet.com/klehal1/ihrh13u6zjpcvem9/wish/2724322886 klehal1 https://padlet.com/klehal1/ihrh13u6zjpcvem9/wish/2724325635 When a transaction starts it is given a timestamp - so if 2 transactions affect the same object - the transaction with the earliest one will be applied first

In order to ensure transactions aren't lost - each object has a read timestamp and a write timestamp - both updated when an object is read or written]]> 2023-09-28 08:53:54 UTC https://padlet.com/klehal1/ihrh13u6zjpcvem9/wish/2724325635 klehal1 https://padlet.com/klehal1/ihrh13u6zjpcvem9/wish/2724328707 This is another serialization technique 

Transactions are ordered in terms of their dependencies on each other as well as the time they were initiated 

It can avoid a deadlock by blocking one request until another is completed]]> 2023-09-28 08:56:41 UTC https://padlet.com/klehal1/ihrh13u6zjpcvem9/wish/2724328707