PostgreSQL提供了引數client_min_messages用以控制返回給客戶的訊息級別，不同的級別返回的訊息大小不同，預設為NOTICE。在通常情況下，如果客戶端執行的SQL語句不頻繁的話，使用預設引數即可，但如果客戶端執行大量的SQL，設定該引數為較高階別就顯得有意義了：可以減少訊息的大小從而降低網路負載，提升吞吐。

**引數簡介**
下面建立一個儲存過程，raise notice顯示通知資訊
```
[local]:5432 pg12@testdb=# CREATE OR REPLACE FUNCTION foo() RETURNS void AS
pg12@testdb-# $$
pg12@testdb$#         BEGIN
pg12@testdb$#                 RAISE NOTICE 'some message';
pg12@testdb$#                 RETURN;
pg12@testdb$#         END;
pg12@testdb$# $$ LANGUAGE 'plpgsql';
CREATE FUNCTION
Time: 389.227 ms
[local]:5432 pg12@testdb=# 
```
執行儲存過程
```
[local]:5432 pg12@testdb=# show client_min_messages;
 client_min_messages 
---------------------
 notice
(1 row)

Time: 0.589 ms
[local]:5432 pg12@testdb=# select foo();
NOTICE:  some message
 foo 
-----
 
(1 row)

Time: 26.838 ms
[local]:5432 pg12@testdb=# set client_min_messages='ERROR';
SET
Time: 0.361 ms
[local]:5432 pg12@testdb=# select foo();
 foo 
-----
 
(1 row)

Time: 1.638 ms
[local]:5432 pg12@testdb=# 
```
在client_min_messages設定為ERROR後，不再顯示NOTICE通知資訊。
下面使用benchmarksql壓測工具測試該引數從NOTICE修改為ERROR後的效能變化。
1.NOTICE
```
[xdb@localhost run]$ ./runBenchmark.sh props.pg
2019-09-25 12:15:25,434  INFO - Term-00, 
2019-09-25 12:15:25,435  INFO - Term-00, +-------------------------------------------------------------+
2019-09-25 12:15:25,435  INFO - Term-00,      BenchmarkSQL v4.1.1
2019-09-25 12:15:25,435  INFO - Term-00, +-------------------------------------------------------------+
2019-09-25 12:15:25,435  INFO - Term-00,  (c) 2003, Raul Barbosa
2019-09-25 12:15:25,435  INFO - Term-00,  (c) 2004-2016, Denis Lussier
2019-09-25 12:15:25,435  INFO - Term-00,  (c) 2016, Jan Wieck
2019-09-25 12:15:25,435  INFO - Term-00, +-------------------------------------------------------------+
2019-09-25 12:15:25,435  INFO - Term-00, 
2019-09-25 12:15:25,435  INFO - Term-00, driver=org.postgresql.Driver
2019-09-25 12:15:25,435  INFO - Term-00, conn=jdbc:postgresql://192.168.26.28:5432/benchmarkdb
2019-09-25 12:15:25,435  INFO - Term-00, user=pg12
2019-09-25 12:15:25,435  INFO - Term-00, 
2019-09-25 12:15:25,435  INFO - Term-00, warehouses=32
2019-09-25 12:15:25,435  INFO - Term-00, terminals=20
2019-09-25 12:15:25,435  INFO - Term-00, runMins=5
2019-09-25 12:15:25,435  INFO - Term-00, limitTxnsPerMin=0
2019-09-25 12:15:25,435  INFO - Term-00, 
2019-09-25 12:15:25,435  INFO - Term-00, newOrderWeight=45
2019-09-25 12:15:25,435  INFO - Term-00, paymentWeight=43
2019-09-25 12:15:25,435  INFO - Term-00, orderStatusWeight=4       Term-00, Running Average 
2019-09-25 12:20:25,706  INFO - Term-00, 52216    Memory Usage: 26MB / 37MB                 
2019-09-25 12:20:25,706  INFO - Term-00,                                                    
2019-09-25 12:20:25,707  INFO - Term-00, Measured tpmC (NewOrders) = 7448.89                
2019-09-25 12:20:25,707  INFO - Term-00, Measured tpmTOTAL = 16626.58                       
2019-09-25 12:20:25,707  INFO - Term-00, Session Start     = 2019-09-25 12:15:25
2019-09-25 12:20:25,707  INFO - Term-00, Session End       = 2019-09-25 12:20:25
2019-09-25 12:20:25,707  INFO - Term-00, Transaction Count = 83171
[xdb@localhost run]$ 
[xdb@localhost run]$ 
```
2.ERROR
```
[xdb@localhost run]$ ./runBenchmark.sh props.pg
2019-09-25 12:22:57,954  INFO - Term-00, 
2019-09-25 12:22:57,954  INFO - Term-00, +-------------------------------------------------------------+
2019-09-25 12:22:57,954  INFO - Term-00,      BenchmarkSQL v4.1.1
2019-09-25 12:22:57,954  INFO - Term-00, +-------------------------------------------------------------+
2019-09-25 12:22:57,954  INFO - Term-00,  (c) 2003, Raul Barbosa
2019-09-25 12:22:57,955  INFO - Term-00,  (c) 2004-2016, Denis Lussier
2019-09-25 12:22:57,955  INFO - Term-00,  (c) 2016, Jan Wieck
2019-09-25 12:22:57,955  INFO - Term-00, +-------------------------------------------------------------+
2019-09-25 12:22:57,955  INFO - Term-00, 
2019-09-25 12:22:57,955  INFO - Term-00, driver=org.postgresql.Driver
2019-09-25 12:22:57,955  INFO - Term-00, conn=jdbc:postgresql://192.168.26.28:5432/benchmarkdb
2019-09-25 12:22:57,955  INFO - Term-00, user=pg12
2019-09-25 12:22:57,955  INFO - Term-00, 
2019-09-25 12:22:57,955  INFO - Term-00, warehouses=32
2019-09-25 12:22:57,955  INFO - Term-00, terminals=20
2019-09-25 12:22:57,955  INFO - Term-00, runMins=5
2019-09-25 12:22:57,955  INFO - Term-00, limitTxnsPerMin=0
2019-09-25 12:22:57,955  INFO - Term-00, 
2019-09-25 12:22:57,955  INFO - Term-00, newOrderWeight=45
2019-09-25 12:22:57,955  INFO - Term-00, paymentWeight=43
2019-09-25 12:22:57,955  INFO - Term-00, orderStatusWeight=4       Term-00, Running Average 
2019-09-25 12:27:58,267  INFO - Term-00, 79156    Memory Usage: 18MB / 37MB                 
2019-09-25 12:27:58,267  INFO - Term-00,                                                    
2019-09-25 12:27:58,267  INFO - Term-00, Measured tpmC (NewOrders) = 7815.72                
2019-09-25 12:27:58,267  INFO - Term-00, Measured tpmTOTAL = 17440.12                       
2019-09-25 12:27:58,267  INFO - Term-00, Session Start     = 2019-09-25 12:22:58
2019-09-25 12:27:58,267  INFO - Term-00, Session End       = 2019-09-25 12:27:58
2019-09-25 12:27:58,268  INFO - Term-00, Transaction Count = 87254
[xdb@localhost run]$ 
```
TPMC 7815 vs 7448，提升比例為4.9%

為免系統隨機擾動導致的誤差，重新測試了一遍
```
-- NONE
2019-09-25 14:53:05,384  INFO - Term-00, Measured tpmC (NewOrders) = 7168.43                
2019-09-25 14:53:05,384  INFO - Term-00, Measured tpmTOTAL = 15890.5                        
2019-09-25 14:53:05,384  INFO - Term-00, Session Start     = 2019-09-25 14:48:05
2019-09-25 14:53:05,385  INFO - Term-00, Session End       = 2019-09-25 14:53:05
2019-09-25 14:53:05,385  INFO - Term-00, Transaction Count = 79491
[xdb@localhost run]$

-- vacuum full;
-- client_min_messages=error
2019-09-25 14:44:29,101  INFO - Term-00, Measured tpmC (NewOrders) = 7239.02                
2019-09-25 14:44:29,101  INFO - Term-00, Measured tpmTOTAL = 16079.06                       
2019-09-25 14:44:29,101  INFO - Term-00, Session Start     = 2019-09-25 14:39:28
2019-09-25 14:44:29,102  INFO - Term-00, Session End       = 2019-09-25 14:44:29
2019-09-25 14:44:29,102  INFO - Term-00, Transaction Count = 80434

-- vacuum full;
-- update_process_title=off
-- track_activities=off
2019-09-25 15:01:11,861  INFO - Term-00, Measured tpmC (NewOrders) = 7253.43                
2019-09-25 15:01:11,861  INFO - Term-00, Measured tpmTOTAL = 16111.73                       
2019-09-25 15:01:11,862  INFO - Term-00, Session Start     = 2019-09-25 14:56:11
2019-09-25 15:01:11,862  INFO - Term-00, Session End       = 2019-09-25 15:01:11
2019-09-25 15:01:11,862  INFO - Term-00, Transaction Count = 80584

-- vacuum full;
-- client_min_messages=error
-- update_process_title=off
-- track_activities=off
2019-09-25 15:08:46,923  INFO - Term-00, Measured tpmC (NewOrders) = 7194.55                
2019-09-25 15:08:46,923  INFO - Term-00, Measured tpmTOTAL = 16059.38                       
2019-09-25 15:08:46,923  INFO - Term-00, Session Start     = 2019-09-25 15:03:46
2019-09-25 15:08:46,923  INFO - Term-00, Session End       = 2019-09-25 15:08:46
2019-09-25 15:08:46,923  INFO - Term-00, Transaction Count = 80350

```
似乎沒有什麼效果。

**參考資料**
[Reducing log messages on the client](https://www.cybertec-postgresql.com/en/reducing-log-messages-on-the-client/)

PostgreSQL DBA(96) - System Conf(client_min_messages)

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