只要被 DROP 或 TRUNCATE 删除的表是在 tikv_gc_safe_point 时间之后

You never want to usemmapin your DBMS if you need to write.

ow we can hide the latency of the disk rather than focusing on optimizations with registersand caches since getting data from disk is so slow.

As the price of gold goes up, miners' higher profit margins can boost earnings exponentially.

One example of a system call that can’t be made asynchronously is file-based system calls

Instead of leaving trust up to chance, you can engineer it by building a repeatable system.

On my worst days, I leave them completely in the dark and go into a cave, emerging from hibernation after days or weeks without any updates.

Go’s hidden #pragmas

Heap usage

hardware timestamp counter (TSC)

compute

samplesp

execute

you may consider the exported providers from a module as the module's public interface, or API.

xdotool search --name "Mozilla Firefox" windowsize 1024 768

Go has the GOGC variable, that can also be controlled with the SetGCPercent function in the runtime/debug package. Don't be afraid to tune the GC to suit your needs.

feedback optimizations

Whether automatically commit a transaction.

cyclical replication

Don’t worry: every mature C++ project is using something other than iostreams for good reasons.

For example, a split pipeline makes it easy to implement caching intermediate data, stealing intermediate data from similar queries running at the same time, and merging pipelines for similar queries.

大部分只涉及单表数据的常用的算子都可以下推到 tikv-server 上计算

All three systems were architected more than 25 years ago, when hardware characteristics were much different than today.

When PD is performing schedule

对于大部分简单的 Transformation Rule，所以 Match() 函数只需要简单地返回 true 就行了。

另外每个优化规则都需要完整的遍历整个逻辑执行计划，添加优化规则的心智负担和知识门槛非常高。

where thequery graph has cycles

hese queries are often optimizedby partitioning the fact table and replicating the dimension tableson all workers

worst-case optimal algorithm forsequential evaluation

communication-optimal algorithmfor distributed evaluation

GreenPlum 是一个基于 PostgreSQL 的 mpp 版本的 db，支持完整的 SQL 语义和各种 db 功能，基本上就可以把他当做一个黑盒的，兼容 PostgreSQL 协议的 db 来用

At the moment, cost-based optimization is only used to select join algorithms: for relations that are known to be small, Spark SQL uses a broadcast join, using a peer-to-peer broadcast facility available in Spark

We also prune cartesian product candidates when building a new plan if there exists no join condition involving references from both left and right subtrees. This pruning strategy significantly reduces the search space.

meet the broadcast criteria.

num(A IJ B) = num(A)*num(B)/max(distinct(A.k),distinct(B.k))

0xffff0 is 16 bytes before the end of the BIOS (0x100000). Therefore we shouldn't be surprised that the first thing that the BIOS does is jmp backwards to an earlier location in the BIOS; after all how much could it accomplish in just 16 bytes?

PC starts executing with CS = 0xf000 and IP = 0xfff0.

because the definition of %x does not dominate all of its uses

thehardware raises the privilege level and starts executing a pre-arranged function in thekernel

hus a process al-ternates between executing inuser spaceandkernel space.

Because there are only local latent variables, we can easily decompose the ELBO into terms Li\mathcal{L}_iL​i​​\mathcal{L}_i that depend only on a single datapoint xix_ix​i​​x_i. This enables stochastic gradient descent.

KL(q​λ​​(z∣x)∣∣p(z∣x))=KL(q_\lambda(z \vert x) \vert \vert p(z \vert x)) = Eq[logqλ(z∣x)]−Eq[logp(x,z)]+logp(x)\mathbf{E}_q[\log q_\lambda(z \vert x)]- \mathbf{E}_q[\log p(x, z)] + \log p(x)E​q​​[logq​λ​​(z∣x)]−E​q​​[logp(x,z)]+logp(x)

By Jensen’s inequality, the Kullback-Leibler divergence is always greater than or equal to zero. This means that minimizing the Kullback-Leibler divergence is equivalent to maximizing the ELBO.

防止意外发布你的代码

interface（接口）关键字将抽象类的概念更延伸了一步，它完全禁止了所有的函数定义

此外，若通过继承增添了一种新类型，如“三角形”，那么我们为“几何形状”新类型编写的代码会象在旧类型里一样良好地工作。所以说程序具备了“扩展能力”，具有“扩展性”。

统一记号法

有两种做法可将新得的派生类与原来的基类区分开。

沿这种思路产生的设计将是非常笨拙的，会大大增加程序的复杂程度。相反，新建类的时候，首先应考虑“组织”对象；这样做显得更加简单和灵活。利用对象的组织，我们的设计可保持清爽。一旦需要用到继承，就会明显意识到这一点。

第二个原因是允许库设计人员修改内部结构，不用担心它会对客户程序员造成什么影响。

第一个原因是防止程序员接触他们不该接触的东西

arcane

in NLP we typically use filters that slide over full rows of the matrix (words).

It makes intuitive sense that you build edges from pixels, shapes from edges, and more complex objects from shapes.