The latest fixes to TTMServer done some months ago are not enough. During translation rally at translatewiki.net, translation memory was using too much cpu time. In addition there have been reports and observations that suggestions are not found, for example when translating the tech news with many repeating parts.
During the Lyon hackathon I spoke with David Chan who suggested to replace the current FuzzyLikeThis query with checking some ngrams from beginning and end of the strings. Those need to be stored separately at indexing time unless there is a way to instruct ES to do it for us. In any case short one to three word strings need special attention.
It seems that current performance bottleneck is fetching too many string contents for comparison and scoring, not the scoring itself.