现在我正在阅读一篇关于http://docs.sequelizejs.com/manual/installation/getting-started.html的文章
并且无法理解下面写的这些句子。
如果您从多个进程连接到数据库，则必须为每个进程创建一个实例，但每个实例的 最大连接池大小应为“最大连接池大小除以实例数”。因此，如果您希望最大连接池大小为 90，并且您有 3 个工作进程，则每个进程的实例的最大连接池大小应为 30。
pool: {
max: 5,
min: 0,
idle: 10000
}
连接池大小是多少？这意味着最大值吗？
我现在正在理解这样的连接池。如果“max”为 5，并且 3 个用户想要访问数据库，则为单个用户分配 3 个连接。
而如果6个用户想要获得DB，5个连接都分配给单个用户，由于只有5个连接，第6个用户必须等待。
所以我无法理解
每个实例的最大连接池大小应为“最大连接池大小除以实例数”。
谁能解释一下？
这是一个非常广泛的问题，但这里是非常广泛的概述
每当我们连接到数据库服务器时，它实际上会派生一个新进程来满足该请求。正如您所料，这很昂贵。所以 pool 允许我们保持数据库服务器中活跃的进程数。max意味着无论您的应用程序（节点）获得多少请求，它都不会使用数据库服务器打开新进程。
而如果6个用户想要获得DB，5个连接都分配给单个用户，由于只有5个连接，第6个用户必须等待。
在上述情况下，只有 5 个并行请求可以与 db 服务器（不是应用服务器）一起运行
这是一个很好的阅读链接
这是一个演示pool.max和pool.idle选项效果的示例。
环境：
"sequelize": "^5.21.3"node：v12.16.1PostgreSQL：9.6客户端代码：
db.ts：
const sequelize = new Sequelize({
dialect: 'postgres',
host: envVars.POSTGRES_HOST,
username: envVars.POSTGRES_USER,
password: envVars.POSTGRES_PASSWORD,
database: envVars.POSTGRES_DB,
port: Number.parseInt(envVars.POSTGRES_PORT, 10),
define: {
freezeTableName: true,
timestamps: false,
},
pool: {
max: 5,
min: 0,
idle: 10 * 1000,
},
});
export { sequelize };
pool_test.ts：
import { sequelize } from '../../db';
for (let i = 0; i < 100; i++) {
sequelize.query('select pg_sleep(1);');
}
通过 docker 容器运行 PostgreSQL 服务器：
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
3c9c0fd1bf53 postgres:9.6 "docker-entrypoint.s…" 5 months ago Up 27 hours 0.0.0.0:5430->5432/tcp node-sequelize-examples_pg_1
运行测试代码：
DEBUG=sequelize* npx ts-node ./pool_test.ts
调试日志：
sequelize:pool pool created with max/min: 5/0, no replication +0ms
sequelize:connection:pg connection acquired +0ms
sequelize:connection:pg connection acquired +38ms
sequelize:connection:pg connection acquired +3ms
sequelize:connection:pg connection acquired +0ms
sequelize:connection:pg connection acquired +1ms
sequelize:connection:pg connection acquired +1ms
sequelize:pool connection acquired +97ms
sequelize:sql:pg Executing (default): select pg_sleep(1); +0ms
Executing (default): select pg_sleep(1);
sequelize:pool connection acquired +2ms
sequelize:pool connection acquired +0ms
sequelize:pool connection acquired +0ms
sequelize:pool connection acquired +0ms
sequelize:sql:pg Executing (default): select pg_sleep(1); +2ms
Executing (default): select pg_sleep(1);
sequelize:sql:pg Executing (default): select pg_sleep(1); +2ms
Executing (default): select pg_sleep(1);
sequelize:sql:pg Executing (default): select pg_sleep(1); +0ms
Executing (default): select pg_sleep(1);
sequelize:sql:pg Executing (default): select pg_sleep(1); +0ms
Executing (default): select pg_sleep(1);
sequelize:sql:pg Executed (default): select pg_sleep(1); +1s
sequelize:pool connection released +1s
sequelize:pool connection acquired +1ms
sequelize:sql:pg Executed (default): select pg_sleep(1); +2ms
sequelize:sql:pg Executed (default): select pg_sleep(1); +0ms
sequelize:sql:pg Executed (default): select pg_sleep(1); +0ms
sequelize:sql:pg Executed (default): select pg_sleep(1); +0ms
sequelize:sql:pg Executing (default): select pg_sleep(1); +1ms
Executing (default): select pg_sleep(1);
sequelize:pool connection released +1ms
sequelize:pool connection released +0ms
sequelize:pool connection released +0ms
sequelize:pool connection released +0ms
sequelize:pool connection acquired +1ms
sequelize:pool connection acquired +0ms
sequelize:pool connection acquired +0ms
sequelize:pool connection acquired +0ms
进入docker容器，查看连接过程：
root@3c9c0fd1bf53:/# date '+%A %W %Y %X' && ps aux | grep "postgres: testuser"
Thursday 31 2020 09:51:34 AM
postgres 13615 0.0 0.7 289496 16064 ? Ss 08:29 0:00 postgres: testuser node-sequelize-examples [local] idle
postgres 14335 0.0 0.5 288384 11248 ? Ss 09:51 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45704) SELECT
postgres 14336 0.0 0.5 288384 11248 ? Ss 09:51 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45706) SELECT
postgres 14337 0.0 0.5 288384 11252 ? Ss 09:51 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45708) SELECT
postgres 14338 0.0 0.5 288384 11248 ? Ss 09:51 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45710) SELECT
postgres 14339 0.0 0.5 288384 11248 ? Ss 09:51 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45712) SELECT
postgres 86437 0.0 0.6 288804 13704 ? Ss 00:57 0:00 postgres: testuser node-sequelize-examples [local] idle
如您所见，有5(pool.max) 个连接进程。
连接处理 IDLE 10(pool.idle)秒后。连接进程将被破坏。
root@3c9c0fd1bf53:/# date '+%A %W %Y %X' && ps aux | grep "postgres: testuser"
Thursday 31 2020 09:53:48 AM
postgres 13615 0.0 0.7 289496 16064 ? Ss 08:29 0:00 postgres: testuser node-sequelize-examples [local] idle
postgres 14352 0.0 0.5 288384 11248 ? Ss 09:53 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45716) idle
postgres 14353 0.0 0.5 288384 11252 ? Ss 09:53 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45718) idle
postgres 14354 0.0 0.5 288384 11248 ? Ss 09:53 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45720) SELECT
postgres 14355 0.0 0.5 288384 11248 ? Ss 09:53 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45722) idle
postgres 14356 0.0 0.5 288384 11248 ? Ss 09:53 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45724) SELECT
root 14440 0.0 0.0 12784 972 pts/3 S+ 09:53 0:00 grep postgres: testuser
postgres 86437 0.0 0.6 288804 13704 ? Ss 00:57 0:00 postgres: testuser node-sequelize-examples [local] idle
root@3c9c0fd1bf53:/# date '+%A %W %Y %X' && ps aux | grep "postgres: testuser"
Thursday 31 2020 09:53:49 AM
postgres 13615 0.0 0.7 289496 16064 ? Ss 08:29 0:00 postgres: testuser node-sequelize-examples [local] idle
postgres 14352 0.0 0.5 288384 11248 ? Ss 09:53 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45716) idle
postgres 14353 0.0 0.5 288384 11252 ? Ss 09:53 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45718) idle
postgres 14354 0.0 0.5 288384 11248 ? Ss 09:53 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45720) idle
postgres 14355 0.0 0.5 288384 11248 ? Ss 09:53 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45722) idle
postgres 14356 0.0 0.5 288384 11248 ? Ss 09:53 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45724) idle
postgres 86437 0.0 0.6 288804 13704 ? Ss 00:57 0:00 postgres: testuser node-sequelize-examples [local] idle
root@3c9c0fd1bf53:/# date '+%A %W %Y %X' && ps aux | grep "postgres: testuser"
Thursday 31 2020 09:53:55 AM
postgres 13615 0.0 0.7 289496 16064 ? Ss 08:29 0:00 postgres: testuser node-sequelize-examples [local] idle
postgres 14352 0.0 0.5 288384 11248 ? Ss 09:53 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45716) idle
postgres 14353 0.0 0.5 288384 11252 ? Ss 09:53 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45718) idle
postgres 14354 0.0 0.5 288384 11248 ? Ss 09:53 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45720) idle
postgres 14355 0.0 0.5 288384 11248 ? Ss 09:53 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45722) idle
postgres 14356 0.0 0.5 288384 11248 ? Ss 09:53 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45724) idle
root 14446 0.0 0.0 12784 932 pts/3 S+ 09:53 0:00 grep postgres: testuser
postgres 86437 0.0 0.6 288804 13704 ? Ss 00:57 0:00 postgres: testuser node-sequelize-examples [local] idle
root@3c9c0fd1bf53:/# date '+%A %W %Y %X' && ps aux | grep "postgres: testuser"
Thursday 31 2020 09:53:58 AM
postgres 13615 0.0 0.7 289496 16064 ? Ss 08:29 0:00 postgres: testuser node-sequelize-examples [local] idle
root 14449 0.0 0.0 12784 940 pts/3 S+ 09:53 0:00 grep postgres: testuser
postgres 86437 0.0 0.6 288804 13704 ? Ss 00:57 0:00 postgres: testuser node-sequelize-examples [local] idle
客户端调试日志：
...
sequelize:pool connection released +25ms
sequelize:pool connection destroy +10s
sequelize:pool connection destroy +0ms
sequelize:pool connection destroy +0ms
sequelize:pool connection destroy +0ms
sequelize:pool connection destroy +1ms
如果更改pool.max为10，请检查连接进程数：
root@3c9c0fd1bf53:/# date '+%A %W %Y %X' && ps aux | grep "postgres: testuser"
Thursday 31 2020 09:56:51 AM
postgres 13615 0.0 0.7 289496 16064 ? Ss 08:29 0:00 postgres: testuser node-sequelize-examples [local] idle
postgres 14457 0.0 0.5 288384 11248 ? Ss 09:56 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45728) SELECT
postgres 14458 0.0 0.5 288384 11252 ? Ss 09:56 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45730) SELECT
postgres 14459 0.0 0.5 288384 11252 ? Ss 09:56 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45732) SELECT
postgres 14460 0.0 0.5 288384 11248 ? Ss 09:56 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45734) SELECT
postgres 14461 0.0 0.5 288384 11248 ? Ss 09:56 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45736) SELECT
postgres 14462 0.0 0.5 288384 11248 ? Ss 09:56 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45738) SELECT
postgres 14463 0.0 0.5 288384 11244 ? Ss 09:56 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45740) SELECT
postgres 14464 0.0 0.5 288388 11244 ? Ss 09:56 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45742) SELECT
postgres 14465 0.0 0.5 288388 11244 ? Ss 09:56 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45744) SELECT
postgres 14466 0.0 0.5 288388 11248 ? Ss 09:56 0:00 postgres: testuser node-sequelize-examples 172.18.0.1(45746) SELECT
root 14472 0.0 0.0 12784 944 pts/3 S+ 09:56 0:00 grep postgres: testuser
postgres 86437 0.0 0.6 288804 13704 ? Ss 00:57 0:00 postgres: testuser node-sequelize-examples [local] idle