1. A computer-implemented system for stream processing, comprising: a stream component for receiving an input stream that includes event imperfections based on speculative execution and for providing consistency in an output, wherein the speculative execution comprises refraction of incorrect events by using a set of operators for removing speculatively produced incorrect output, the output produced by the speculative execution of a streaming operator is non-blocking; the set of operators for providing multiple consistency levels by varying blocking time and data retention time in memory, wherein blocking time exposes a tradeoff between a degree of speculation and latency and data retention time in memory exposes a tradeoff between state size and correctness, via which consistency in the output is guaranteed, and the consistency is varied on a per query basis via the set of operators; and a microprocessor that executes computer-executable instructions associated with at least one of the stream component or the set of operators.