Our SharePoint 2010 farm's crawl DB was at 250 GB which is very unusual. According to this post the size of the crawl DB should be 0.046 × (sum of content databases). Sum of my content DB size is around 1TB and the crawl DB size should be around 46 GB.
Finally decided to reduce the size of it by applying host distribution rules or shrink the crawl DB. I chose to do the second option and did the following. Now the crawl DB size is close to the 45 GB .
1) Central Admin-> Search service admin -> Index Reset. This will erase all the content Index.
2) DB Server->Choose the Crawl DB ->Shrink the Crawl DB files. This will shrink all the mdf/ldf files and size of your DB will be meager.
3) Kicked off a full crawl.
But the shortcoming of these steps is I lost the entire crawl history. Hope this post helps you as well.