本节简单介绍了PostgreSQL 12 在日志记录上的改进：Don't log incomplete startup packet if it's empty。 >This will stop logging cases where, for example, a monitor opens a connection and immediately closes it. If the packet contains any data an incomplete packet will still be logged. Author: Tom Lane 对于每一个客户端连接，PG都会请求Postmaster，然后fork一个后台进程来处理请求，Postmaster期望每一个客户端请求发送startup message给PG Server，startup packet中的信息用于配置fork的后台进程。对于端口扫描、HA解决方案中的心跳检测等等都会发请求给PG Server port，PG会启动进程来处理这些连接，但安全检测、HA脚本等不同于常规的客户端，对于这些请求，PG会产生一条日志条目，因此会造成日志文件的膨胀而导致不必要的IO开销。 **PG 11** 使用工具nc来访问数据库端口，日志中会产生无用的日志条目。 ``` [xdb@localhost ~]$ psql -c 'select version();' Timing is on. Expanded display is used automatically. version --------------------------------------------------------------------------------------------------------- PostgreSQL 11.2 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-16), 64-bit (1 row) Time: 56.253 ms [xdb@localhost ~]$ [xdb@localhost ~]$ for i in {1..100}; do nc -zv localhost 5110 ; done Ncat: 0 bytes sent, 0 bytes received in 0.01 seconds. Ncat: Version 7.50 ( https://nmap.org/ncat ) Ncat: Connected to ::1:5110. Ncat: 0 bytes sent, 0 bytes received in 0.01 seconds. Ncat: Version 7.50 ( https://nmap.org/ncat ) Ncat: Connected to ::1:5110. Ncat: 0 bytes sent, 0 bytes received in 0.01 seconds. Ncat: Version 7.50 ( https://nmap.org/ncat ) Ncat: Connected to ::1:5110. Ncat: 0 bytes sent, 0 bytes received in 0.01 seconds. Ncat: Version 7.50 ( https://nmap.org/ncat ) Ncat: Connected to ::1:5110. Ncat: 0 bytes sent, 0 bytes received in 0.01 seconds. ... ``` 数据库日志输出 ``` 2019-12-09 14:35:55.468 CST,,,16065,"::1:57554",5dedeb4b.3ec1,1,"",2019-12-09 14:35:55 CST,,0,LOG,08P01,"incomplete startup packet",,,,,,,,,"" 2019-12-09 14:35:55.479 CST,,,16067,"::1:57556",5dedeb4b.3ec3,1,"",2019-12-09 14:35:55 CST,,0,LOG,08P01,"incomplete startup packet",,,,,,,,,"" 2019-12-09 14:35:55.490 CST,,,16069,"::1:57558",5dedeb4b.3ec5,1,"",2019-12-09 14:35:55 CST,,0,LOG,08P01,"incomplete startup packet",,,,,,,,,"" 2019-12-09 14:35:55.503 CST,,,16071,"::1:57560",5dedeb4b.3ec7,1,"",2019-12-09 14:35:55 CST,,0,LOG,08P01,"incomplete startup packet",,,,,,,,,"" 2019-12-09 14:35:55.513 CST,,,16073,"::1:57562",5dedeb4b.3ec9,1,"",2019-12-09 14:35:55 CST,,0,LOG,08P01,"incomplete startup packet",,,,,,,,,"" ... ``` 这些日志其实是无用的日志信息，可以不作记录。 **PG 12** ``` [xdb@localhost ~]$ psql -h localhost -p 5120 -U pg12 -c 'select version();' Timing is on. Expanded display is used automatically. version --------------------------------------------------------------------------------------------------------- PostgreSQL 12.1 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-16), 64-bit (1 row) Time: 60.207 ms [xdb@localhost ~]$ [xdb@localhost ~]$ for i in {1..100}; do nc -zv localhost 5120 ; done Ncat: 0 bytes sent, 0 bytes received in 0.01 seconds. Ncat: Version 7.50 ( https://nmap.org/ncat ) Ncat: Connected to ::1:5120. Ncat: 0 bytes sent, 0 bytes received in 0.01 seconds. Ncat: Version 7.50 ( https://nmap.org/ncat ) Ncat: Connected to ::1:5120. Ncat: 0 bytes sent, 0 bytes received in 0.01 seconds. Ncat: Version 7.50 ( https://nmap.org/ncat ) Ncat: Connected to ::1:5120. Ncat: 0 bytes sent, 0 bytes received in 0.01 seconds. Ncat: Version 7.50 ( https://nmap.org/ncat ) Ncat: Connected to ::1:5120. Ncat: 0 bytes sent, 0 bytes received in 0.01 seconds. Ncat: Version 7.50 ( https://nmap.org/ncat ) Ncat: Connected to ::1:5120. Ncat: 0 bytes sent, 0 bytes received in 0.01 seconds. [xdb@localhost ~]$ ... ``` 数据库日志信息，相对于PG 11，没有出现无用的日志信息 ``` [pg12@localhost ~]$ tail -f $PGDATA/pg_log/postgresql-2019-12-09.log 2019-12-09 14:18:59.317 CST [1813] LOG: ending log output to stderr 2019-12-09 14:18:59.317 CST [1813] HINT: Future log output will go to log destination "csvlog". ``` **参考资料** [PostgreSQL 12 Improvement: Benign Log Entries “Incomplete Startup Packet” ](https://www.percona.com/blog/2019/12/03/postgresql-12-improvement-benign-log-entries-incomplete-startup-packet/) [PATCH](https://git.postgresql.org/gitweb/?p=postgresql.git;a=patch;h=342cb650e)