Question 1084

One in a Hundred

A search request fans out to 100 backend shards in parallel and waits for all of them. Each shard independently answers within 10ms for 99 percent of calls. Roughly what fraction of user requests take longer than 10ms?

A

About 10 percent, since parallel execution divides the tail probability by the fan-out factor

B

About 63 percent, because the parent waits on the slowest shard and 0.99^100 is only about 0.37

C

About 1 percent, because the shards are independent and the slow cases average out across them

D

About 37 percent, which is the chance that at least one shard exceeds its 10ms threshold