遍历数据库中的所有记录时,我们首先想到的是Model.all.each.但是,当数据量很大的时候(数万?),这就不怎么合适了,因为Model.all.each会一次性加载所有记录,并将其实例化成 Model 对象,这显然会增加内存负担,甚至耗尽内存. 对于ActiveRecord 而言,有个find_each专门解决此类问题.find_each底层依赖于find_in_batches,会分批加载记录,默认每批为1000. 对Mongoid而言,话说可以直接用Person.all.each,它会自…

平台: VMware上装的Ubuntu-15.10 环境准备工作:装Fortran, lapack, blas, cblas (理论上装好lapack后面两个应该是自动的),其他的有需要的随时安装就可以 =====  开始编译 ===== cd到CorrsTmplt的目录 1. sleep的error 在命令行执行 make 此时,出现error FileManagement.cpp:25:25: error: ‘sleep’ was not declared in this scope sle…

http://www.onjava.com/pub/a/onjava/2001/05/30/optimization.htmlComparing the performance of LinkedLists and ArrayLists (and Vectors) (Page last updated May 2001, Added 2001-06-18, Author Jack Shirazi, Publisher OnJava). Tips: ArrayList is faster than…

Performance Considerations for Entity Framework 5 By David Obando, Eric Dettinger and others Published: April 2012 1. Introduction Object-Relational Mapping frameworks are a convenient way to provide an abstraction for data access in an object-orient…

Stream API Overview Before we look into Java 8 Stream API Examples, let’s see why it was required. Suppose we want to iterate over a list of integers and find out sum of all the integers greater than 10. Prior to Java 8, the approach to do it would b…

1. Detecting Performance Issues 2. Scripting Strategies 3. The Benefits of Batching 4. Kickstart Your Art 5. Faster Physics 6. Dynamic Graphics 7. Masterful Memory Management 8. Tactical Tips and Tricks 1. Detecting Performance Issues  The Unity Prof…

原文转自:https://bourgeois.me/rest/ REST APIs are a very common topic nowaday; they are part of almost every web application. A simple, consistent and pragmatic interface is a mandatory thing; it will be much easier for others to use your API. Even if th…

Executors In all of the previous examples, there's a close connection between the task being done by a new thread, as defined by its Runnable object, and the thread itself, as defined by aThread object. This works well for small applications, but in…

High Level Concurrency Objects So far, this lesson has focused on the low-level APIs that have been part of the Java platform from the very beginning. These APIs are adequate for very basic tasks, but higher-level building blocks are needed for more…

Apache Kafka is an attractive service because it's conceptually simple and powerful. It's easy to understand writing messages to a log in one place, then reading messages from that log in another place. This simplicity not only allows for a nice sepa…