Should I run db statistics twice during one maintainance window?
2 answers
You're right. you only need once. The purpose is to keep the plans updates to the best
Although make sure you're not collecting only a sample, and running it to all tables, ok?
SQL : https://msdn.microsoft.com/en-us/library/ms187348.aspx
Oracle : https://docs.oracle.com/cd/B28359_01/server.111/b28274/stats.htm#PFGRF003
DB2 : http://www.ibm.com/support/knowledgecenter/SSEPGG_10.1.0/com.ibm.db2.luw.admin.cmd.doc/doc/r0001980.html