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2021 latest software test classic interview questions - answer and see?

2021-08-10 08:14:17 Test Mengmeng

The Internet

Briefly describe TCP agreement

TCP: Transmission control protocol , Is the transport layer communication protocol . It has connection oriented 、 reliable 、 Byte stream transmission, etc

TCP When establishing a connection , Three handshake protocols are required

TCP The process of three handshakes is as follows :

The client sends SYN Heat preservation to the server , Get into SYN_SEND(SEQ=X) state

Server received SYN Heat preservation , In response to a SYN(SEQ=Y) ACK(ACK=X+1) message , Get into SYN_RECV state

The client receives... From the server SYN message , In response to a ACK(ACK=Y+1) message , Start connection

TCP/IP What is the role ?

TCP/IP The protocol is a set of network communication standards , So that different devices around the world can communicate

TCP And UDP The difference between ?

TCP Transmission control protocol .UDP User datagram protocol

TCP There are many requirements for resources ,UDP Less resource requirements

TCP Can guarantee the correctness of the data ,UDP It's possible to lose your bag

TCP It can ensure the order of data ,UDP No guarantee

The Internet 7 The layer model is that 7 layer ? List some specific application examples

From bottom to top , The physical layer 、 Data link layer 、 The network layer 、 Transport layer 、 The session layer 、 The presentation layer 、 application layer

The physical layer : Coaxial cable 、 Receiver 、 Transmitter, etc

Data link layer : network card 、 Switch 、 bridge

The network layer : Router 、 gateway

Transport layer :TCP agreement 、UDP agreement

The session layer :SQL、ASP、 PHP etc.

The presentation layer :ASCII、JPEG、PNG、MP3 etc.

application layer :telnet、ssh、http、smtp etc.

How to test whether the network is connected ?

Use ping command

What way can I connect to the home host through the Internet ?

telnet

How to let the Internet access the terminal at home ? What is its principle ?

Open remote desktop on your computer

Use teamview

Their principle is :

You and the other machine build a Socket Connect

Virtualize an opponent's system locally

The other party's system will be in this Socket Send real-time data of its system status on the connection

Data received , This virtual system restores the other system's operation through this data

Operate the virtual operating system locally , Will send data commands to the other machine

Receive instructions from the repeater , adopt Hook( Bottom hook ) To the operating system

Then the cycle

What is the process of accessing a web site ?

Here are a few simple processes

First, you need to find... Through the domain name IP, If the local cache does not require a request DNS The server

obtain IP Then start shaking hands with the destination host three times to establish TCP Connect

After the connection is established HTTP visit , Transfer disease to get web content

After the transmission is completed, shake hands with the destination host four times and disconnect TCP Connect

2Linux

Linux What are the common commands , And briefly describe their role

ls View current directory

df-h Check disk usage

kill Kill the process

top View the current host status

mv Moving files

cp Copy file

netstat-a View port usage status

rm Delete

cat see file

vim How to quit

q Exit without saving

wq Exit after saving

q! Forced exit

How to view the contents of a large file page by page ?

cat filename.txt | more Through pipeline commands and more Realization

How to view linux Port number occupied ?

netstat -a View port status

How to view process status ?

ps -ef | grep Process name

chown What is it? ?grep What is it? ?

chown Change the owner and group of the file

gerp Look for strings in the file that match the criteria

How to view logs ?

tail -f Log file name

5 A client passes TCP Connect to host , How to view this 5 A connection ?

netstat -nat|grep ESTABLISHED

3 database

What methods can improve the efficiency of database query ?

Index , Using index

Query only the necessary fields

Handle reasonably NULL Field

Use with caution like Equal wildcard

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What should we pay attention to in index design ?

Index field length cannot be too long

The number of indexes cannot be too many

Database update statement ?GROUP BY How to use ?

UPDATE TABLENAME SET Field name = The new value WHERE Column name = The old value

GROUP BY It is generally used to group query results

# If you want to group the results , add SUM Function

SELECT SUM( Name 1) Order 2 FROM TABLENAME

WHERE Name 1 Name 2

GROUP BY Order 1

If a data table has thousands of records , The visit was slow , What are the ways to optimize ?

MySQL

mysql The index of , Left most matching principle

Indexing can speed up the retrieval of data . Common are B+Tree Indexes , Hash index .

Left most matching principle :

When the index is a federated index , In the query condition ,mysql Hit from the far left , If a range query appears (>、<、between、like), You can't hit further , Then it degenerates to linear search , The order of columns determines the number of columns that can hit the index .

mysql Master-slave replication of

mysql In order to maintain high availability , It will adopt a master-slave structure , One master node , Multiple slave node ,master Nodes can write , and slave Nodes can only read .

binlog Threads : Write data changes on the primary server to the binary log

I/O Threads : Read binary logs from the primary server , And write it to the replay log of the slave server

SQL Threads : Read the replay log and replay SQL sentence

mysql Clustered index of 、 Nonclustered indexes

Clustered index : Index created with primary key , The data in the table is stored on the leaf node

Nonclustered indexes : Indexes created with non primary keys , The leaf node stores the primary key and index columns

When using a nonclustered index to find data , Get the primary key on the leaf and find the data you want to find .( Back to the table )

mysql Joint index , What to pay attention to ?

A federated index consists of multiple columns (a,b,c,d) form , Pay attention to index hits , Left most matching principle , Hit from the left , When a range query is encountered, it cannot be further matched .

Why does the database use B+ Tree to implement the index ?

Fewer searches (B+ Trees are fatter than red and black trees )

Use the disk read ahead feature ( once IO Can fully load a node )

4 Programming

HTTP Agreement GET and POST The difference between

1、get The request focuses on getting resources from the server , and post The request focuses on sending data to the server .

2、get Data is transmitted through URL request , With field =value In the form of , use ? Connect to URL after , Between multiple request data & Connect , This process is visible to the user , unsafe , Parameter exposure .post The transmission data is to seal the field and corresponding value in the request entity and send it to the server , This process is invisible to the user , Hidden requests , It's safer than .

3,get The amount of data transmitted is small , suffer URL Length limitation , But it's efficient .post The amount of data transmitted is unlimited , It can transmit a lot of data , So when transferring files, you can only use post, But it's less efficient . When there are many requests, a request queue may be formed .

4,get The way only supports ASCII character , Therefore, there may be garbled code when transmitting Chinese to the server .post Support for standard character sets , It can transfer Chinese characters correctly .

HTTPS How to create a request ?

HTTPS = HTTP + SSL(Secure Sockets Layer, Secure socket layer )

HTTPS It can prevent eavesdropping ( Asymmetric key encryption )、 Anti camouflage 、 tamper-proof ( Encryption and authentication )

The client sends the request to the server

Server side returns certificate and public key , The public key exists as part of the certificate

The client verifies the validity of the certificate and public key , If effective , Then generate the shared key and send it to the server using public key encryption

The server uses the private key to decrypt the data , And encrypt the data with the received shared key , Send to client

The client uses the shared key to decrypt the data

SSL Encryption establishment …


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