[10000truths]

Every RDBMS out there has an option to configure a DB-enforced transaction timeout. But that configuration is tied to a connection, not to a transaction. So using that configuration means giving up connection pooling. Which a lot of people don't want to do because it impacts latency and DB resource usage.

[frollogaston]

Every xact within a given connection will use the same connection-wide config, but the timeout is counting how long a single transaction takes, right? I don't see why you'd need to give up pooling for this unless you need different settings per xact.

[10000truths]

Pooling means you're sending multiple queries (from different HTTP requests) over the same DB connection. A well-designed DB wire protocol will allow for pipelining those queries:

[send Query 1] -> [send Query 2] -> [send Query 3] -> [receive Result 1] -> [receive Result 2] -> [receive Result 3]

But in Postgres and MySQL, pipelined queries are not executed in parallel. They're just queued up for a single thread (per connection) to execute sequentially. Thus, if Query 1 is a transaction that takes too long, then it ends up blocking the execution of Query 2 and Query 3.