I've made a gist to replace the 'getConnection' function for mediawiki 1.34. 1) Edit the file: mediawiki/includes/libs/redis/RedisConnectionPool.php
2) Replace 'getConnection' function with this one from the gist.
3) This adds 4 line of code at the top:
global $wgRedisDatabase;
if (is_null($wgRedisDatabase)) {
$wgRedisDatabase = 0;
}
4) Near the bottom, add "$conn->select($wgRedisDatabase);"
See this gist: https://gist.github.com/yombo/81ac7c5be47ccc28c3b1b5c43d90dcc2