How to perform efficient incremental update of a git repo from a large SVN repo? Bug or clueless user?

I have a large and active SVN repository. More than 36,000 revisions, thousands of branches - new ones created daily - and a non-standard layout. Also, a secondary git repository that serves as a faithful "git" copy of the work accumulating in SVN (git version 2.9.5). I seek an efficient way to

Efficient incremental update of a git repo from a large SVN repo. Bug or clueless user?

I have a large and active SVN repository. More than 36,000 revisions, thousands of branches - new ones created daily - and a non-standard layout. Also, a secondary git repository that serves as a faithful "git" copy of the work accumulating in SVN (git version 2.9.5). I seek an efficient way to