Some questions in the telecommunications written test
1. Linux incremental backup recovery sequence
Cumulative incremental backup
In a business application with a large amount of data, it is unrealistic to fully back up the Linux system every day, so an incremental backup strategy needs to be used.
Cumulative incremental backup refers to performing a full backup first. After the server has been running for a period of time, the difference between the backup data of the current system and the full backup is compared, and only the data with differences is backed up.
Let's say we do a full backup on day one. During the incremental backup on the second day, only the differential data between the second day and the first day will be backed up; during the incremental backup on the third day, only the differential data between the third day and the second day will be backed up. The advantage of using cumulative incremental backup is that the backup requires less data, takes less time, and takes up less space; the disadvantage is that data recovery is more troublesome. If it is the example in Figure 1, then when performing data recovery, The data of the full backup must be restored first, and then the data of the first incremental backup, the data of the second incremental backup, and the data of the third incremental backup must be restored in order, and finally all data can be restored.
2. The order of arithmetic operators, logical operators, comparison operators
Arithmetic operators > Comparison operators > Logical operators
3. How to delete a view
DROP VIEW
4. Three major characteristics of database
- Data structuring, data structuring is the fundamental difference between database and file system;
- Data is highly shareable, low in redundancy, and easy to expand;
- The independence of data is high, including the physical independence of data and the logical independence of data.
5. Characteristics of transactions
The four major characteristics of transactions: atomicity, consistency, isolation, and durability;
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Atomicity
The atomicity of a transaction means that the transaction must be an atomic operation sequence unit. Each operation included in the transaction is only allowed to appear in one of two states during one execution, either all of them succeed or all of them fail.
Any operation will cause the entire transaction to fail, and other operations that have been performed will be undone and rolled back. Only when all operations are successful, the entire transaction will be considered successful. -
Consistency
Transaction consistency means that the execution of a transaction cannot destroy the integrity and consistency of the database data. The database must be in a consistent state before and after a transaction is executed.
For example: Zhang San transfers money to Li Si. It is impossible that Zhang San’s money was deducted and Li Si did not add money. -
Isolation
Transaction isolation means that in a concurrent environment, concurrent transactions are isolated from each other, and the execution of one transaction cannot be interfered with by other transactions. In other words, when different things do not operate on the same data, each transaction has a complete data space.
The operations and data used within a transaction are isolated from other concurrent transactions, and transactions executed concurrently cannot interfere with each other. -
Durability
of a transaction means that once the transaction is submitted, the data in the database must be permanently saved. Even if the server system crashes or the server is down, etc. As long as the database is restarted, it can be restored to the state after the transaction successfully ended.
6. If multiple interrupts occur at the same time, how should the order be handled?
When multiple interrupts occur at the same time, the system will process the interrupt request with the highest priority first according to the interrupt priority. You can use () to adjust the corresponding order of interrupt events.
A. Interrupt nesting B．Interrupt vector C. Interrupt response D. Interrupt masking
Interrupt priority is specified by hardware and cannot be changed, but the response order of interrupt events can be adjusted through interrupt masking.
7. Teardrop attack
Teardrop uses (a) in the IP datagram
A. The function of the offset field
B. The function of the protocol field
C. The function of the identification field
D. The function of the lifetime field
Teardrop attack principle
The implementation principle of this attack is to send abnormal data packet fragments to the target host, so that the IP data packet fragments have overlapping parts during the reassembly process, causing the target system to be unable to reorganize them, further causing the system to crash and stop service. Vicious attack.
8. The role of spanning tree protocol
1. When using the spanning tree algorithm, in an Ethernet network, create a spanning tree with a certain port of a certain switch as the root to avoid loops.
2. When the Ethernet network topology changes, the purpose of convergence protection is achieved through the spanning tree protocol.
9. A switch or bridge without VLAN is connected to 4 hosts. What are the collision domains and broadcast domains?
Layer 2 devices such as switches and bridges isolate conflict domains, and level 3 devices such as routers isolate broadcast domains.
- When counting how many conflict domains there are, it depends on how many devices are connected to the switch or bridge. How many conflict domains there are (including routers)
- When counting how many broadcast domains there are, it depends on how many devices are connected to the router. How many broadcast domains there are.
10. Flag bits of ARM processor
When the ARM processor compares the size of unsigned numbers, it judges based on the (c) flag bit.
AC and N
BC and V
CZ
DZ and V