I have not tried this, so the following might not be true, but: One important thing to note here is that meta.amazon_asin is not covered by any of the paths of any SearchField of SearchRelease or any of the extrapath entries. This means that its content is not eagerly loaded and you run into the n+1 problem (http://use-the-index-luke.com/sql/join/nested-loops-join-n1-problem, https://secure.phabricator.com/book/phabcontrib/article/n_plus_one/). If you use the --sqltimings option during indexing, you'll see that for every release that's getting processed, one select [...] from release_meta statement for every single release instead of loading them once along with the releases. Adding meta.amazon_asin to extrapaths should fix this. Situations like this are the sole reason extrapaths exists.

Sorry, the second I was about to close the other tab with the definition of SearchRelease I noticed that it does in fact already load all the asins for the asin field, so ignore the previous comment.