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PostgreSQL is Enough

• Just Use Postgres for Everything
• Simplify: move code into database functions

Background Jobs

• https://github.com/citusdata/pg_cron

Message Queues

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See also:

• Free database hosting
• https://free-for.dev/#/?id=iaas
• https://free-for.dev/#/?id=paas

Service	Type	RAM	Storage	Limitations
👉 Adaptable	PaaS	256 MB	Non-persistent? (1 GB database storage available)
AWS EC2	IaaS	1 GB		⚠️ Only free for 1 year

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See also:

• Free backend hosting
• https://free-for.dev/#/?id=dbaas

Service	Type	Storage	Limitations
Amazon DynamoDB	⚠️ Proprietary NoSQL	25 GB	⚠️ Payment method required
Amazon RDS	⚠️ Proprietary RDBMS		⚠️ Only free for 1 year
Azure SQL Database	MS SQL Server		⚠️ Only free for 1 year
👉 Clever Cloud	PostgreSQL, MySQL, MongoDB, Redis	256 MB (PostgreSQL)	Max 5 connections (PostgreSQL)

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package main

import (
	"fmt"
	"net"
	"os"
	"syscall"
)

const (

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# Detect operating system in Makefile.
# Author: He Tao
# Date: 2015-05-30

OSFLAG 				:=
ifeq ($(OS),Windows_NT)
	OSFLAG += -D WIN32
	ifeq ($(PROCESSOR_ARCHITECTURE),AMD64)
		OSFLAG += -D AMD64
	endif

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public class LRUCache {
    class DLinkedNode {
        int key;
        int value;
        DLinkedNode prev;
        DLinkedNode next;
    }

    private DLinkedNode head, tail;

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int a[maxn];
int lowbit(int x)
{
    return x&(-x);
}
void add(int x,int y)
{
    while(x<=n)
    {
        a[x]+=y;

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int find(int x)
{
    if(x!=fa[x])
        fa[x]=find(fa[x]);
    return fa[x];
}
void union(int x,int y)
{
    int a=find(x),b=find(y);
    if(a!=b)

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import cv2
# cam = cv2.VideoCapture(0)   # local camera
# cam = cv2.VideoCapture("/path/to/video")  # open video
cam = cv2.VideoCapture("rtsp://admin:password123@192.168.1.64:554")
# 设置摄像头尺寸
cam.set(cv2.CAP_PROP_FRAME_WIDTH, 64)
cam.set(cv2.CAP_PROP_FRAME_HEIGHT, 48)
# 获取摄像头尺寸
while True:
    ret, frame = cam.read()

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public class Foo {
    // immutability
    private final int a;
    private final int b;
    private final int c;
    private final int d;
    private final int e;

    public static class Builder {
        private final int a;