最近，在Ubuntu18下搭建PostgreSQL10.06测试环境，添加rum插件没有问题，但是在添加pg_jieba的时候碰到了cannot create PGC_POSTMASTER variables after startup问题。
在postgres的源码guc.c里头，有这么一句：
1 /* 2 * Only allow custom PGC_POSTMASTER variables to be created during shared 3 * library preload; any later than that, we can't ensure that the value 4 * doesn't change after startup. This is a fatal elog if it happens; just 5 * erroring out isn't safe because we don't know what the calling loadable 6 * module might already have hooked into. 7 */ 8 if (context == PGC_POSTMASTER && 9 !process_shared_preload_libraries_in_progress) 10 elog(FATAL, "cannot create PGC_POSTMASTER variables after startup");
说是需要在共享库预加载的时候才能够创建PGC_POSTMASTER变量，但是尝试了重启系统并不能解决任何问题。
最后在/etc/postgresql/10/main/postgresql.conf文件中，找到如下一行，添加pg_jieba：
shared_preload_libraries = ‘pg_jieba’
重新启动postgres服务。这时候再使用命令查看动态库状态：
# SHOW shared_preload_libraries; shared_preload_libraries -------------------------- pg_jieba (1 row) SHOW
jieba插件已经显示预加载了。这时候再创建扩展：
# CREATE EXTENSION "pg_jieba"; CREATE EXTENSION
成功启动_(:з」∠)_