Mark Sandler

Frugal Streaming for Estimating Quantiles

Modern applications require processing streams of data for estimating statistical quantities such as quantiles with small amount of memory. In many such applications, in fact, one needs to compute such statistical quantities for each of a large number of groups (e.g.,network traffic grouped by source IP address), which additionally restricts the amount of memory available for the stream for any particular group. We address this challenge and introduce frugal streaming, that is algorithms that work with tiny – typically, sub-streaming – amount of memory per group.

Theory research at Google

Through the history of Computer Science, new technologies have emerged and generated fundamental problems of interest to theoretical computer scientists. From the era of telecommunications to computing and now, the Internet and the web, there are many such examples. This article is derived from the emergence of web search and associated technologies, and focuses on the problems of research interest to theoretical computer scientists that arise, in particular at Google.

Understanding latency variations of black box services

Data centers run many services that impact millions of users daily. In reality, the latency of each service varies from one request to another. Existing tools allow to monitor services for performance glitches or service disruptions, but typically they do not help understanding the variations in latency. We propose a general framework for understanding performance of arbitrary black box services. We consider a stream of requests to a given service with their monitored attributes, as well as latencies of serving each request. We propose what we call the multi-dimensional f-measure, that helps for a given interval to identify the subset of monitored attributes that explains it. We design algorithms that use this measure not only for a fixed latency interval, but also to explain the entire range of latencies of the service by segmenting it into smaller intervals. We perform a detailed experimental study with synthetic data, as well as real data from a large search engine. Our experiments show that our methods automatically identify significant latency intervals together with request attributes that explain them, and are robust.