[apache] Can't open file 'svn/repo/db/txn-current-lock': Permission denied

It's permission problem. It is not "classic" read/write permissions of apache user, but selinux one.

Apache cannot write to files labeled as httpd_sys_content_t they can be only read by apache.

You have 2 possibilities:

  1. label svn repository files as httpd_sys_content_rw_t:

    chcon -R -t httpd_sys_content_rw_t /path/to/your/svn/repo
    
  2. set selinux boolean httpd_unified --> on

    setsebool -P httpd_unified=1
    

I prefer 2nd possibility. You can play also with other selinux booleans connected with httpd:

getsebool -a | grep httpd