Search for summaries in the quick search is very slow, for a couple of

reasons. We didn't have an index on the summary, but even if we did,

we were looking for text in the middle of the summary field, which

indexes can't help with.
This could cause real problems on large installs, slowing down the

database making it nearly impossible to find what you're looking for.

Continuing to type would trigger further expensive queries, eventually

resulting in other queries stalling on the server.
To fix this, we now have an index, and we now search only the beginnings

of summaries. We also only start searching if we have 4 or more

characters. It limitation on where we search sucks, but it's better than

nothing.
Theoretically, we could use the search index, but more work must be done

to make that happen.
We could also, theoretically, use the full-text search feature for

MySQL, but not all versions support that for InnoDB. Work would need to

be done to introspect whether we can use full-text search, and it would

require hand-applying some SQL to the database. It also wouldn't buy us

anything for other types of databases.
This may limit the usefulness of quick search for summaries until we

come up with something clever, but at least it won't break servers.

Tested search locally. It didn't check summaries until I entered my 5th

character. Then it did prefix matching instead of searching within text.
Tested the query with MySQL using EXPLAIN, and saw that it was using the

index and substantially limited the number of rows it had to search.