The Two Machines

Everything you need to know about query planning can be understood from this query: SELECT * FROM xy WHERE y = 3 ORDER BY x Imagine we have two indexes, one ordered on y, and one ordered on x. Then two possible plans suggest themselves: Plan 1: scan the y index, restricting it to the values of y such that y = 3, then sort the result by x. Plan 2:...

Everything you need to know about query planning can be understood from this query: SELECT * FROM xy WHERE y = 3 ORDER BY x Imagine we have two indexes, one ordered on y, and one ordered on x. Then two possible plans suggest themselves: Plan 1: scan the y index, restricting it to the values of y such that y = 3, then sort the result by x. Plan 2:...

“This code’s no good,” says Pittsford, pointing at the screen: def update_and_get_balance(account, amount): database.debit(account, amount) return database.get_balance(account) Sol, the author of the code, peers over his shoulder and squints. “What’s wrong with it? It adds the amount, then gets back the new balance.” Pittsford shakes his...

“This code’s no good,” says Pittsford, pointing at the screen: def update_and_get_balance(account, amount): database.debit(account, amount) return database.get_balance(account) Sol, the author of the code, peers over his shoulder and squints. “What’s wrong with it? It adds the amount, then gets back the new balance.” Pittsford shakes his...

I hope everyone had a good weekend. I went on a hike. It was great. Statistics One of my great school regrets, next to “taking three years of business classes,” is taking less statistics than I did, which was basically the bare minimum. It was, in fact the bare minimum: one probability class and one statistics class. In my defense, my probability...