How can I force Rails to synchronize transactions to a MySQL table across connections?

I have a high-traffic site that records web hits in a table, Hits. There's logic in place so that duplicate hits are discarded (where the definition of what defines a hit as duplicate is arbitrary for the purposes of this example).

Problem: with multiple web servers running (against the same DB), two or more hits can arrive at the same time on differe开发者_开发技巧nt web servers and, from each server's perspective, none of them are duplicates (whereas were they serialized through a single server all but the first should be discarded). Hence, all of them get written to the Hits table.

Without altering the DB schema to force uniqueness on a field in the Hits table, how do I force Rails to synchronize the transaction to the database to guarantee that no duplicates are written? According to the documentation, ActiveRecord transactions are only enforced on a per-connection basis, which isn't good enough (as far as I can tell).

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Transactions in MySQL are always per-connection, there's no other way to tell what is an atomic operation.

I think the only way to do this is either by placing a lock on the whole table or to enforce the integrity on the schema level.