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1 ABSTRACT

Mergesort 优点：

• 不受数据倾斜影响
• 适于通过向量化执行来进行并行处理
• 适于多线程操作操作

Origami:

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1 #9: Optimizations past their prime

1.1 Best practices

– 可能的情况下编写清晰、惯用的代码
Prefer writing clear, idiomatic code whenever possible. It is not only easier to read and debug, but in the long run, also easier for the compiler to optimize.

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1 Introduction

PostgreSQL 审计扩展（pgAudit）通过标准的 PostgreSQL 日志记录功能提供详细的会话和/或对象审计日志。

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1 Abstract

2 INTRODUCTION

• What is a filter

  属于近似查询 (approximate membership query), 用于判断独具是否在集合中。

  • 如果输入在集合中，则必定输出 Yes
  • 如果不在集合中，则输出 Yes 的概率不能多于 \(\Sigma\)

• What are filters used for
  • 与精确查询相比
    • 更省资源， 与数据量无关，而与 Σ （误报率）有关
    • 适于放在内存中，用于真正操作之前来过滤掉无效数据
      • 比如 join

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1 ABSTRACT

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1 TOOLS

1.1 top

1.2 ps

1.3 vmstat – Virtual Memory Statistics

1.4 sar – System Activity Repoter

1.5 perf

1.6 tubostat

1.7 iostat

1.8 irqbalance

1.9 ss – socket statistics

1.10 numastat

1.11 numad

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1 RTFM…

1.1 ipcs

1.2 ipcrm

2 Check shared memory in Linux

Print active shared memory segments using -m option.

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# ipcs -m
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
0x00000000 65536 root 600 393216 2 dest
0x00000000 98305 root 600 393216 2 dest

where,

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1 Referencing local array

std::initializer_list 在使用中会转化成为常量对象的匿名局部数组：

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std::initializer_list<int> wrong() { // for illustration only!
    return { 1, 2, 3, 4};
}
int main() {
    std::initializer_list<int> x = wrong();
}

The above code is equivalent to the following:

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A table in PostgreSQL has a relfilenode value, which specifies the file name of the table on disk (except foreign table and partition table). In general, this value can be found in the relfilenode field of the pg_class table, but there are some specific tables whose query result in the relfilenode field is 0. This blog will explore the kernel processing of these special tables relfilenode.