TCP keepalive可用於：
1、使網路連線處於活躍（相對於Idle而言）狀態
2、檢測在沒有關閉網路連線情況下的通訊中斷

本節介紹OS和PG的相關引數說明和配置。

**OS配置**

```
keepalive idle time: tpc連線處於空閒狀態下，超過該時間則傳送keepalive packet；2 hours on both Linux and Windows
keepalive interval: 如keepalive packet沒有應答，則在間隔後再次傳送packet；75 seconds on Linux, 1 second on Windows
keepalive count: 傳送packet的次數；9 on Linux, 10 on Windows (this value cannot be changed on Windows)
```
在Linux中，可透過如下配置
```
# On Linux, this is done by editing the /etc/sysctl.conf file:
# detect dead connections after 70 seconds
net.ipv4.tcp_keepalive_time = 60
net.ipv4.tcp_keepalive_intvl = 5
net.ipv4.tcp_keepalive_probes = 3
```
使用命令生效
```
sysctl -p
```

**PG引數配置**
```
keepalives_idle：為0則使用OS配置
keepalives_interval：為0則使用OS配置
keepalives_count：為0則使用OS配置
```

**參考資料**
[TCP keepalive for a better PostgreSQL experience](https://www.cybertec-postgresql.com/en/tcp-keepalive-for-a-better-postgresql-experience/)
[LIBPQ-KEEPALIVES-IDLE](https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-KEEPALIVES-IDLE)

PostgreSQL DBA(187) - TCP keepalive

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