minimal database list retrieval

Information schema access isn't particularly well optimized. As such, at least in older versions, fetching from the information_schema.TABLES would involve opening every table. The ANSI SQL standards SCHEMATA provides a quicker way, and we can reuse it.

Author: grooverdan

mysqltuner.pl

@@ -239,6 +239,9 @@ package main;
 # Checks for supported or EOL'ed MySQL versions
 my ( $mysqlvermajor, $mysqlverminor, $mysqlvermicro );
 
+# Database
+my @dblist;
+
 # Super structure containing all information
 my %result;
 $result{'MySQLTuner'}{'version'} = $tunerversion;
@@ -5849,8 +5852,8 @@ sub mysql_databases {
  return;
  }
 
- my @dblist = select_array(
-"SELECT DISTINCT TABLE_SCHEMA FROM information_schema.TABLES WHERE TABLE_SCHEMA NOT IN ( 'mysql', 'performance_schema', 'information_schema', 'sys' );"
+ @dblist = select_array(
+"SELECT SCHEMA_NAME FROM information_schema.SCHEMATA WHERE SCHEMA_NAME NOT IN ( 'mysql', 'performance_schema', 'information_schema', 'sys' );"
  );
  infoprint "There is " . scalar(@dblist) . " Database(s).";
  my @totaldbinfo = split /\s/,
@@ -6027,9 +6030,6 @@ sub mysql_tables {
  if (mysql_version_ge(8) and not mysql_version_eq(10)) {
  infoprint "MySQL and Percona version 8 and greater have remove PROCEDURE ANALYSE feature"
  }
- my @dblist = select_array(
-"SELECT DISTINCT TABLE_SCHEMA FROM information_schema.TABLES WHERE TABLE_SCHEMA NOT IN ( 'mysql', 'performance_schema', 'information_schema', 'sys' );"
- );
  foreach (@dblist) {
  my $dbname = $_;
  next unless defined $_;