# Transaction Processing

We often get asked how FoundationDB can achieve high performance for transaction processing over a scalable, distributed cluster. Here is a brief overview.

## The transactional authority

Because FoundationDB supports concurrent operations by clients, it uses a distributed set of nodes working together as a transactional authority to detect conflicting updates. Transactions execute using optimistic concurrency control, so they don’t need to lock a key before updating it and unlock it afterward. Instead, when a transaction is submitted to the transactional authority, it will be rejected if there has been a conflicting transaction, requiring the client to retry the rejected transaction.

## Transaction servers

To maintain high performance, the transactional authority is implemented by a number of individual transaction servers, each of which manages a portion of the incoming stream of transactions. FoundationDB’s design decomposes transaction processing into its individual functions and scales them independently. The separate functions are:

- batching incoming transactions;

- checking transaction conflicts;

- logging transactions;

- durably storing the data.

Of these functions, many people intuitively focus on transaction conflict checking stage as a potential bottleneck. Fortunately, it turns out that this function is scalable. FoundationDB uses a sophisticated data-parallel and multithreaded algorithm to optimize conflict-checking so that it requires only a small percentage of the system’s total work. This optimization allows a few transaction servers to keep up with a large cluster of storage servers.