根據同步流複製模式，需要等待至少一個備庫接受wal並返回確認資訊後主庫才向客戶端返回成功，一方面保障資料完整性，另一方面如果備庫宕機，主庫的寫操作將出現等待狀態，實驗環境為一主一備

模擬備庫故障

[postgres@localhost pg_root]$ pg_ctl stop -m fast
waiting for server to shut down....2021-11-01 05:15:10.927 EDT [3890] LOG:  received fast shutdown request
2021-11-01 05:15:10.928 EDT [3890] LOG:  aborting any active transactions
 
2021-11-01 05:15:10.928 EDT [3895] FATAL:  terminating walreceiver process due to administrator command
2021-11-01 05:15:10.929 EDT [3892] LOG:  shutting down
2021-11-01 05:15:10.932 EDT [3890] LOG:  database system is shut down
 done
server stopped

在主庫上查詢，查詢不受影響

postgres=# select * from ceshizhujixieru;
 id
----
  2
 

(1 row)

在主庫上插入資料，一直除以等待狀態

通常一主一備不會採用同步複製，因為備庫宕機後會對生產產生影響，postgresql支援一主多備，