In previous article, we have introduced the columnar storage of Dremel. In this paper summary, we will focus on running query on tree structure records in Dremel.

Dremel is a scalable, interactive ad-hoc query system for analysis of read-only nested data.

Funtion Definition

The return value cannot be an array. Everything else is possible. (Interestingly, even though a C++ function can’t return an array directly, it can return an array that is part of a structure or object.)

Arrays

Declaring an array:

typeName arrayName[arraySize]

arraySize must be a integer constant, const value or const expression, for which all values are known at compilation time. In particular, arraySize cannot be a variable whose value is set at run time.

If need to dynamically allocate an array at run time, use new or malloc.

在这篇文章当中我们介绍过用Valine支持阅读量和评论的方法。

Task cancellation

An activity is cancellable if external code can move it to completion before its normal completion.

浮点数的表示

实数数的二进制表示

计算机用浮点数表示实数，二进制层面的表示和十进制是十分类似的：

整数的表示

无符号数与有符号数

无符号数的表示非常直接，因为没有符号，k位的二进制就表示0 ~ 2^k - 1范围内的整数。对于 [x_{k - 1}, x_{k - 2}, …, x₀]，其表示的值为：

Executing tasks in threads

The first step in organizing a program around task execution is identifying sensible task boundaries. Ideally, tasks are independent activities: work that doesn’t depend on the state, result, or side effects of other tasks. Independence facilitates concurrency, as independent tasks can be executed in parallel if there are adequate processing resources.

Synchronized collections

The synchronized collection classes include Vector and Hashtable, which achieve thread safety by encapsulating their state and synchronizing every public method so that only one thread at a time can access the collection state,