Oracle执行计划 讲解(二)
现在我们讲讲Oracle执行计划里面每个参数的含义 我们以下面的一个例子来讲解 这里做个补充:trace的类型一共有以下几种 序号
现在我们讲讲Oracle执行计划里面每个参数的含义
我们以下面的一个例子来讲解
这里做个补充:trace的类型一共有以下几种
序号
命令
解释
1
SET AUTOTRACE OFF
此为默认值,即关闭Autotrace
2
SET AUTOTRACE ON EXPLAIN
只显示执行计划
3
SET AUTOTRACE ON STATISTICS
只显示执行的统计信息
4
SET AUTOTRACE ON
包含2,3两项内容
5
SET AUTOTRACE TRACEONLY
与ON相似,但不显示语句的执行结果
我喜欢SET AUTOTRACE TRACEONLY,我们以后的例子都是基于这种方式的
让我们来一行一行的看:一、表部分
1、Plan hash value:
2、Operation( 操作)
这里的东西就多了,就是把sql进行分解,让我一起看看上的sql,这段sql的第一步是employee_id=25,这里我们employee_id上面建了主键,建主键默认创建唯一索引。这里是用“=”进行限制的,所以走的unique scan方式。其他方式参考Oracle执行计划 讲解(一)内容
还有一个知识点,就是要知道表链接操作,见我的另外一篇文章()
3、Name(被操作的对象)
比如上例中的第二行operation(TABLE ACCESS BY INDEX ROWID)这里的TABLE对象为EMPLOYEES
4、Row,有的地方也叫Cardinality(用plsqldev里面解释计划窗口)
这里是数据查询的行数,比如说上个例子第4行, departments 这张表就要扫描27行,然后和子查询(select b.department_id from employees b where b.employee_id=205)的值进行比较。如果使用=(注:大部分时候是不能用=来替换,这里是特例)就不一样了。
5、Byte
扫描的数据的字节数
6、Cost
这里上次讲过了,这里简单说下吧。
cost没有单位,是一个相对值,是sql文以cbo方式解析执行时,供oracle用来评估cbo成本,选择执行计划用的。
公式:Cost=(Single block I/O cost+ Multiblock I/O cost+ CPU cost)/sreadtim
没有明确的含义,不过对比时就非常有用了。
7、Time
每段执行的时间

Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

AI Hentai Generator
Generate AI Hentai for free.

Hot Article

Hot Tools

Notepad++7.3.1
Easy-to-use and free code editor

SublimeText3 Chinese version
Chinese version, very easy to use

Zend Studio 13.0.1
Powerful PHP integrated development environment

Dreamweaver CS6
Visual web development tools

SublimeText3 Mac version
God-level code editing software (SublimeText3)

Hot Topics

0.What does this article do? We propose DepthFM: a versatile and fast state-of-the-art generative monocular depth estimation model. In addition to traditional depth estimation tasks, DepthFM also demonstrates state-of-the-art capabilities in downstream tasks such as depth inpainting. DepthFM is efficient and can synthesize depth maps within a few inference steps. Let’s read about this work together ~ 1. Paper information title: DepthFM: FastMonocularDepthEstimationwithFlowMatching Author: MingGui, JohannesS.Fischer, UlrichPrestel, PingchuanMa, Dmytr

DDREASE is a tool for recovering data from file or block devices such as hard drives, SSDs, RAM disks, CDs, DVDs and USB storage devices. It copies data from one block device to another, leaving corrupted data blocks behind and moving only good data blocks. ddreasue is a powerful recovery tool that is fully automated as it does not require any interference during recovery operations. Additionally, thanks to the ddasue map file, it can be stopped and resumed at any time. Other key features of DDREASE are as follows: It does not overwrite recovered data but fills the gaps in case of iterative recovery. However, it can be truncated if the tool is instructed to do so explicitly. Recover data from multiple files or blocks to a single

If you need to know how to use filtering with multiple criteria in Excel, the following tutorial will guide you through the steps to ensure you can filter and sort your data effectively. Excel's filtering function is very powerful and can help you extract the information you need from large amounts of data. This function can filter data according to the conditions you set and display only the parts that meet the conditions, making data management more efficient. By using the filter function, you can quickly find target data, saving time in finding and organizing data. This function can not only be applied to simple data lists, but can also be filtered based on multiple conditions to help you locate the information you need more accurately. Overall, Excel’s filtering function is a very practical

The performance of JAX, promoted by Google, has surpassed that of Pytorch and TensorFlow in recent benchmark tests, ranking first in 7 indicators. And the test was not done on the TPU with the best JAX performance. Although among developers, Pytorch is still more popular than Tensorflow. But in the future, perhaps more large models will be trained and run based on the JAX platform. Models Recently, the Keras team benchmarked three backends (TensorFlow, JAX, PyTorch) with the native PyTorch implementation and Keras2 with TensorFlow. First, they select a set of mainstream

I cry to death. The world is madly building big models. The data on the Internet is not enough. It is not enough at all. The training model looks like "The Hunger Games", and AI researchers around the world are worrying about how to feed these data voracious eaters. This problem is particularly prominent in multi-modal tasks. At a time when nothing could be done, a start-up team from the Department of Renmin University of China used its own new model to become the first in China to make "model-generated data feed itself" a reality. Moreover, it is a two-pronged approach on the understanding side and the generation side. Both sides can generate high-quality, multi-modal new data and provide data feedback to the model itself. What is a model? Awaker 1.0, a large multi-modal model that just appeared on the Zhongguancun Forum. Who is the team? Sophon engine. Founded by Gao Yizhao, a doctoral student at Renmin University’s Hillhouse School of Artificial Intelligence.

Facing lag, slow mobile data connection on iPhone? Typically, the strength of cellular internet on your phone depends on several factors such as region, cellular network type, roaming type, etc. There are some things you can do to get a faster, more reliable cellular Internet connection. Fix 1 – Force Restart iPhone Sometimes, force restarting your device just resets a lot of things, including the cellular connection. Step 1 – Just press the volume up key once and release. Next, press the Volume Down key and release it again. Step 2 – The next part of the process is to hold the button on the right side. Let the iPhone finish restarting. Enable cellular data and check network speed. Check again Fix 2 – Change data mode While 5G offers better network speeds, it works better when the signal is weaker

Recently, the military circle has been overwhelmed by the news: US military fighter jets can now complete fully automatic air combat using AI. Yes, just recently, the US military’s AI fighter jet was made public for the first time and the mystery was unveiled. The full name of this fighter is the Variable Stability Simulator Test Aircraft (VISTA). It was personally flown by the Secretary of the US Air Force to simulate a one-on-one air battle. On May 2, U.S. Air Force Secretary Frank Kendall took off in an X-62AVISTA at Edwards Air Force Base. Note that during the one-hour flight, all flight actions were completed autonomously by AI! Kendall said - "For the past few decades, we have been thinking about the unlimited potential of autonomous air-to-air combat, but it has always seemed out of reach." However now,

This week, FigureAI, a robotics company invested by OpenAI, Microsoft, Bezos, and Nvidia, announced that it has received nearly $700 million in financing and plans to develop a humanoid robot that can walk independently within the next year. And Tesla’s Optimus Prime has repeatedly received good news. No one doubts that this year will be the year when humanoid robots explode. SanctuaryAI, a Canadian-based robotics company, recently released a new humanoid robot, Phoenix. Officials claim that it can complete many tasks autonomously at the same speed as humans. Pheonix, the world's first robot that can autonomously complete tasks at human speeds, can gently grab, move and elegantly place each object to its left and right sides. It can autonomously identify objects
