Evolution of database architecture
In the era of less business data, we can use a single-machine database to meet the business use. With more and more business requests, the amount of data in the database increases rapidly. At this time, the single-machine database can no longer meet the performance requirements of the business, and the database master-slave replication architecture comes into being.
Master-slave replication separates the write operation from the read operation of the database, uses multiple slaver replication to process the read request, Master to process the write reques...
The following demo introduces the use of reflection mechanism to read notes.
First, custom annotations, one to annotate classes, and another to annotate properties, such as the following demo
package Annotation;
import java.lang.annotation.ElementType;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;
public class TestAnn { @Target(value= {ElementType.TYPE }) @Retention(RetentionPolicy.RUNTIME) public @interface ann{//Used to convert class names to table names. String value();} @Target(value= {ElementType.FIELD }) ...
Write in front of
There are many similar articles on the internet, but on the same road, others may go smoothly and stumble on their own. Record the process of building your own course.
Environmental preparation
1，jira7.3The operation is dependent on the Java environment, that is to say, it is necessary to install JDK and if more than 1.8, it is as follows:
View installed version: RPM -qa|grep java*
You can choose to have multiple versions of the JDK coexist, and I’m simply rude — uninstalled
There are two ways to uninstall, one is normal deletion, the other is strong deletio...
development environment:
> two, configuration
1.GOPATH：This is your working directory. Please add a new GOPATH to the system to specify your working directory and create a new one in the working directory.bin,pkg,srcThree folders.
2.Git：Add the bin directory under the GIT installation directory to the Path environment variable.
3.Using vscode to open the SRC folder, add two files as follows:
{
"files.autoSave": "onFocusChange",
"go.buildOnSave": true,
"go.lintOnSave": true,
"go.vetOnSave": true,
"go.buildTags": "",
"go.buildFlags": [],
"go.lintFlags":...
Description
Given an array of size n, find the majority element. The majority element is the element that appears more than ⌊ n/2 ⌋ times.
You may assume that the array is non-empty and the majority element always exist in the array.
Example 1:
Input: [3,2,3]
Output: 3
Example 2:
Input: [2,2,1,1,1,2,2]
Output: 2
Problem Description: given a non empty array, find the most frequent element exceeding N/2 times.
Idea: The simplest and crudest way to traverse the array, the number of occurrences of each element and elements as a key-value pair to save the form, and finally t...
SQLoptimization
In order to improve the query efficiency in SQL query, we often take some measures to optimize the query statement sql, the following summary of some methods, there is a need for reference.
1.To optimize queries, avoid full table scanning as much as possible, and consider indexing the columns involved in where and order by first.
2.You should try to avoid null value judgments on fields in the where clause, otherwise it will cause the engine to abandon the use of indexes for full table scanning, such as:
select id from t where num is null
You can set a defaul...
Summary: On Linux servers or Python-installed machines, you can use nohup python-m SimpleHTTP Server [port] amp; quickly build an HTTP service.
Python comes with a Web server, SimpleHTTP Server, on a Linux server or on a machine with Python installed.
We can easily use python-m SimpleHTTP Server to quickly build an HTTP service that provides a web service for browsing files.
WindowsSystem operation is as follows
step1:Open the CMD command window
Enter the path of the project
step2:Start service
The order is as follows:
python -m SimpleHTTPServer 8000
Using the above command, you can pub...
1.For synchronous fifo, 80 data can be written per 100 cycles, 8 data can be read per 10 cycles, and the depth of FIFO is at least?
2.If you only use 2 selected 1MUX to complete XOR logic, how many MUX do you need at least?
The answer to the question at the beginning is as follows: there are 3 needs to be verified.
Later, it was found that the correction was not very correct. At least two needed to be corrected.
3.What is the function of anti-aliasing filter before signal sampling? What kind of filter does it choose? How to determine its cut-off frequency?
According to Nyquist Sampli...
