GFS(Google File System)

GFS is a scalable distributed file system, used in large-scale, distributed, a large amount of data access application. It runs on cheaper hardware, but can provide fault tolerance function. It can give a large number of users to provide overall high performance service.

GFS is the Google File System, Google company in order to store massive data and design of the special file system.

1, design overview

( 1) design scenario

GFS and past distributed file system has many of the same goals, but the GFS design by the current and expected application of the workload and technical environment of the drive, which reflects its early file system with distinct ideas. This requires the traditional selection for re-inspection and completely different design perspective.

GFS and before the file system views are as follows:

The 1 part is no longer as abnormal, wrong, but as a common condition to be treated. Because the file system is composed of hundreds to thousands of used for storing machine composition, and these machines are made of inexpensive ordinary components and a large number of guest client access. The number of components and quality makes some machines can not work and some also may not be able to recover. So real-time monitoring, fault detection, fault tolerant, automatic recovery system is essential.

In 2, according to the traditional standard, file is very large. Length up to several GB file is very common. Each file usually contains many application object. When often to deal with rapid growth, including tens of thousands of objects, the length of the TB data set, we very difficult to manage tens of thousands of KB scale file block, even if the underlying file system support. Therefore, the design of operation parameters, the size of the block must reconsider. For large file management must be able to achieve efficient, for a small file must also support, but does not have to optimize.

3, most file update is performed by adding new data, rather than a change in the existing data. In a document of the random operation in practice almost does not exist. Once finished, the file is read only, many data have these characteristics. Some data may comprise a large warehouse for data analysis procedures and description. There is a program in execution of continuous data streams generated. Some archives nature of the data, some are in a machine to produce, in addition to a machine for processing the intermediate data. Because of these large file access method, add operation become the performance optimization and ensuring atomicity of focus. While in the client cache data block is lost their appeal.

In 4, the workload is mainly composed of two components: read operation on large amounts of data stream mode read operations and to a small amount of data in random mode read operations. Before a read operation, may want to read a few hundred KB, usually up to 1MB and more. From a customer's continuous operation is usually read a contiguous area. Random read operation is usually in a random offset read several KB. Performance sensitive applications will usually on a small amount of data read operation for classifying and batch so that the read operation and steady advance, and do not let it to and fro reading.

5, work also contains many large amounts of data, continuous, add data to the file write operation. Write data and read similar scale. Once finished, the file is little changed. In a random location on a small amount of data write operation is also supported, but not very efficient.

6, the system must realize definition intact a large number of customers at the same time to the same file add operational semantics.

( 2) the system interface

GFS provides a similar to the file system interface, although it did not achieve the standard API to POSIX. File in the directory according to the level of organized by path name and logo.

( 3) the system structure

A GFS cluster consists of a master and a chunkserver form, and by many customers to access ( Client ). As shown in figure 1. Master and chunkserver are usually run user layer service process of Linux machine. As long as the resource and reliability allows, chunkserver and client can run on the same machine.

The file is divided into blocks of fixed size. Each block by a constant, globally unique 64 digit Chunkhandle logo, Chunkhandle in block created by master distribution. ChunkServer will block as Linux files stored on a local disk and can be read and written by Chunkhandle and the range of the specified data. For reliable considerations, each block is copied to multiple chunkserver. By default, the preservation of 3 copies, but it can be specified by the user.

Master file system so the meta data ( metadata ), including the name space, access control information, from the document to the mapping block and the block 's current position. It also controls system range of activities, such as block lease ( lease ) management, orphan piece of garbage collection, chunkserver inter block migration. Master regularly through the HeartBeat message with each chunkserver communication, chunkserver transfer instruction and collect its state.

Application of the GFS associated with each customer code implementation of the file system API and master and chunkserver communication to represent the application program to read and write data. The client and master exchange only on metadata ( metadata ) operation, all data communication are directly in contact with chunkserver.

Passenger door and chunkserver are not cached file data. Because the user buffer benefits very little, this is because the data is too much or the working set is too large to cache. Not to cache data simplified the client programs and the whole system integration, because there is no need to consider the cache coherence problem. But the user cache metadata ( metadata ). Chunkserver also does not need to cache files, because when the block as a local file storage.

8 simple fitness to help you stay away from obesity

No time has become not fitness, not exercise the greatest excuse for the fact that as long as you are still moving, it has been unwittingly carry out the different intensity of exercise. The following describes the eight kinds of super-simple exercise, a person weighing 75 kg exercises can burn 100 calories. 1 Bowling Go to the movies with, as bowling, bowling is a very interesting group competition sports, playing 27 minutes you can consume 100 calories. 2 dog Studies have shown that dogs are usually tall people better than no pets, because dogs have to go out every day the reason. As mankind's most loyal "friend", dogs can also become hard to go out power walking. If you follow the dog 18 minutes to 6.5 km / h (equivalent to walking 109 meters per minute) rate to go, you can consume 100 calories. 3 swimming Swimming is one of the most intense aerobic exercise, and not prejudicial to the joints, can strengthen muscles, balance and endurance. Moreover, swimming burns calories fast, 14-minute swim time will be able to consume 100 calories. If high-intensity swim breaststroke swimming, eight minutes to consume 100 calories. 4 skipping In intensity, jumping rope is comparable to swimming and running (10 km per hour) movement. But with the other two sports are different, you can jump rope without leaving home. As long as a rope, a more open space, eight minutes to consume 100 calories. 5 cooking Nothing better than hands-on opportunity to meet their own standards, so if you cook, you can ensure that the food is healthy and beneficial. Moreover, cooking 33 minutes you can consume 100 calories. 6. Sweeping Foreigners are very popular garden by cleaning the leaves for fitness, although this is not a pure sense of the movement, but the sweeping movements, including walking, squatting, carrying, pushing, pulling, etc. If cleaning the school yard or 21 minutes can burn 100 calories. 7. Dance Dance aerobic exercise is one of the famous, and very interesting, if you do not like the demanding dance, disco, ballroom and even the square, there are many popular dances. 15-minute dance will be able to consume 100 calories, or even open your computer or audio, create their own in the room dancing the "dance" can be. 8 washing / window cleaning Not only washing and cleaning anything that can help you burn calories, but more effective way of washing. Car wash, or Ca Chuanghu 18 minutes you can consume 100 calories.

Broccoli healthy secret

Friends, success is inseparable from the diet fitness. If you always pay attention to some fitness recipes or feeding of single words, you'll find out the green cauliflower, broccoli almost everywhere. Then today to talk about why flowers in New Zealand and fitness recipes on emergence rate so high.

The maximum nutrition vegetables -- broccoli

One, nutritional value:

Broccoli broccoli nutritious, containing protein, fat, phosphorus, iron, carotene, vitamin B1, vitamin B2 and vitamin C, vitamin A, especially vitamin C rich, each containing 100 grams of 88 mg, second only to the chili peppers, vegetables in the highest content of a; containing 3.5 grams of protein, 4.5 grams, is cauliflower, tomato 3 times 4 times. Its delicate texture, taste sweet and delicious, easy to digest, to protect blood beneficial.

PS: every time after exercise will sweat, trace elements in the human body is also a serious loss, while eating broccoli can timely supplement these trace elements.

In two, the anticancer efficacy:

The United States and other countries scientists found, broccoli containing" sopho Ruffin" can stimulate cell manufacturing on the beneficial and protective enzyme of type II enzyme. This has the very strong anticancer activity of enzyme, can make the cell formation against foreign carcinogens erosion of the membrane, to prevent a variety of cancers has played a positive role. Long-term consumption can reduce breast cancer, colorectal cancer and gastric cancer risk.

Three, therapeutic effect:

In 1, broccoli 's high vitamin C content, can enhance liver detoxification capacity, enhance immunity, is conducive to human growth and development.

2, children eat can protect vision, improve memory, maintain normal bone growth.

3, with 30 grams of Broccoli Soup, a regular diet, can be heat-clearing and detoxifying, diuresis purge.

4, rich in vitamin K, can maintain vascular willful, is not easy to be broken; but also including prevents infection, promote vascular cleaning of flavonoids.

Read the text above, you will want to, in the end so the cooking broccoli is the most nutrition? Now tell you the answer: the clean cut with hot boiling water boiled just remove cooked ( 12 minutes, not long, keep green ).

1, alone or with other dishes to do cold plate.

2, can also be reentry hot pot rapid seasonings and stir fry pan. With lily, cashews, dried seafood, mushrooms, meat, onions and tomatoes with scrambled, broccoli to put. In conclusion broccoli cooking and processing principle is first boiled water, heating time not long remain green, so as to maintain its nutrition ( boiled water to cool dish, taste or best).

Editor's note: an advertisement word: broccoli is good, but do not do too much oh. After the fitness, nutrition needs much food, not just this one, such as the intake of protein. In short, to balance nutrition ingestion, food material diversification.

MIMO (Multiple-Input Multiple-Out-put)

MIMO ( Multiple-Input Multiple-Out-put ) system is an application on the key technology of 802.11n. 802.11n IEEE following 802.11b \ a \ g new wireless LAN technology, speed up to 600Mbps. At the same time, proprietary MIMO technology can improve the existing 802.11a / B / G network performance. The technique was first proposed in 1908 by Marconi, which uses multiple antennas to suppress channel fading. According to the sending and receiving ends of antenna number, relative to the ordinary SISO ( Single-Input Single-Output ) system, MIMO can also include SIMO ( Single-Input Multi-ple-Output ) and MISO ( Multiple-Input Single-Output ) system.

Summary

MIMO said multiple input multiple output. Read / maimo / or / MIMO /, usually the former British Americans, read the latter, the study of international experts in the field and more are read / maimo /. Typically used for IEEE 802.11n, but can also be used for other 802.11 technology. MIMO is sometimes called the space diversity, because of its use of multiple spatial channels for transmitting and receiving data. Only site ( mobile ) or access point ( AP ) to support MIMO to deploy MIMO.

Advantage

MIMO has the advantage of being able to increase and improve the performance of wireless range. Connected to the old 802.11g access point 802.11n sites with higher speed connection to the farther distance. For example, if you use the old site, from a distance of 25 feet is connected to the access point speed is 1Mbps; and the use of 802.11n MIMO site speed for 2Mbps. To increase the range of 2Mbps, allows the user to farther distances remain connected.

The radio signals transmitted by reflection, will have a signal. Each signal is a spatial flow. The use of single input single output ( SISO ) of the current or the old system one can only send or receive a spatial flow. MIMO allows for multiple antenna for simultaneously transmitting and receiving a plurality of spatial flow. It allows the antenna to transmit and receive simultaneously.

The old access point to the old client - only to send and receive a space flow MIMO access point to the MIMO client - simultaneously transmitting and receiving multiple spatial flow can be seen, the channel capacity with the number of antennas increases linearly. That is to say you can use the MIMO channel increase the capacity of wireless channel, without increasing the bandwidth and transmitting power condition, spectrum utilization rate can be enhanced greatly.

The use of MIMO technology can improve the capacity of the channel, but also can improve the reliability of channel, reduce the error rate. The former is the use of MIMO channel provided spatial multiplexing gain, the latter is the use of MIMO channel to provide space diversity gain. Realization of spatial multiplexing gain algorithm mainly Baer lab BLAST algorithm, ZF algorithm, MMSE algorithm, ML algorithm. ML algorithm has good decoding performance, but the complexity of relatively large, for real-time wireless communication can not meet the requirements. ZF algorithm is simple and easy to implement, but the channel's SNR higher. The performance and complexity of the optimal BLAST algorithm. This algorithm is actually using the ZF algorithm with interference cancellation technology derived. At present, the field of MIMO technology another is the research hotspot of space-time coding. Common space time code with space-time block codes, space-time trellis codes. Space-time codes of the main idea is to use the space and time of the code to achieve a certain space diversity, time diversity, thereby reducing the channel bit error rate.

Web4.0

Web4.0

They also rely on technological progress, enjoy the technological advances, but master, awareness and understanding of technical progress ability is different. The Web system is one of the greatest inventions of mankind so far, is also the most far-reaching influence human computer performance. Then, we look at how the Web and its technology development?

Web1.0 - information sharing

Although people for information sharing has struggled for many years, but it was not until the appearance of Web technology and gradually improve today, information sharing is also far from satisfactory. But compared to before other techniques, such as FTP, self-description given Web system powerful vitality, make Web becomes the first facility information sharing.

Web2.0 - Information Building

Until the era of the Web1.0, information also are one-way, issued by the discourse group. Ordinary people only listen to share, while Web2.0 gives ordinary people the same discourse, consciousness is all-time and active, especially in the ideology prison society. This will inevitably lead to the network information overflow : pitfalls in virus infested, now became the first antivirus software computer applications; information rubbish everywhere, if found suitable for their own information, has become the users needs, so the search engine to rise.

But search engines can not put an end to trap virus, also cannot distinguish the rubbish information, not systematic Web information, so the technical exploration has become inevitable.

Web3.0 -- knowledge transmission

The computer is human consciousness, its progress every point, are necessarily polymerization more wisdom. Gather human wisdom for human to share, computer science and technology is the immanent essence. Web3.0, we should not only destroy the trap virus, kicked out of rubbish information, more orderly system of whole world Web, to the Web resource base for the construction of a" Web library", realize the human" knowledge transmission".

My intellectual product system, is a realization of human knowledge in Web3.0 system. Immediacy is its main characteristic, thus the instant communication ( IM ) system is the intellectual technology platform.

Web4.0 -- knowledge distribution

In Web3.0, humans can easily obtain all kinds of knowledge, these knowledge are the first people instant contribution out. The instant, refers to the school teachers teach the students immediately. From the beginning of Web3.0, network has instant characteristics. But the people do not know how to should acquire knowledge, i.e. their suitable for which knowledge to study. For example, a child of 10 years old want to at the age of 20 to become a nuclear physicist, then he should learn knowledge? The problem is Web4.0 -- the core of knowledge distribution system to solve the problem.

Web5.0 - Pragmatic Web

When it comes to the Pragmatic Web, really into my field of study. Technology development is see things in a blur, but the essence is very simple. The existing computer technology are the Turing machine model, simply put, a Turing machine is mechanization, program, or arithmetic, with data and operator ( operator ) to 2 yuan closed theory system. Turing machine is studied and defined in the data set on the operator rule or law of mathematics science.

In the network world, this closed system should be combined, as a whole, the whole network into a computer system. This computer is no longer a Turing machine, but Petri net. In the early 20 years ago, Petri said, Petri network computer systems technology called pragmatics. Therefore the language network is the computer technology foundation.

Often eat fresh corn longevity and health

Corn, the North known cob, corn is in the south, the development of modern science and technology have bred sweet corn, sweet corn, glutinous corn, sweet corn, or even black corn, variety.

Corn is rich in nutrition, in addition to containing a variety of nutrients, including protein and fat than rice, noodles and Hamish, fat half of linoleic acid, and lecithin, vitamin A, E etc.. Linoleic acid can reduce cholesterol, prevent its deposition in the vascular wall, on the prevention of hypertension, cardiovascular and cerebrovascular diseases have a positive effect.

The United States scientists with corn oil feed cows produce whole milk, found a linoleic acid ( CLA ), it can be the prevention of melanoma, breast cancer, colon cancer, ovarian cancer, prostate cancer, because this kind of linoleic acid can clear the cells of the oxygen free radicals, protection of DNA ( deoxyribonucleic acid free of damage ), can prevent cell mutation induced by cancer, corn contains glutathione also has anti-cancer effect.

Corn germ is particularly rich in vitamin E, it can enhance the body the new supersedes the old., modulates the neural and endocrine function, and the subcutaneous tissue and. Skin cells, elastic and glossy. Nutrition at home are pointed out such as food in 2 / 3 to 1 / 3 of rice, corn, then protein utilization rate can be improved from 58% to 71%, this is called the complementary action of protein.

Edible fresh corn in six, it is good, too tender too much water, too old to starch increased protein decreased, poor taste. Corn cleaning cooking best Decoction thirsty too, such as with corn to be boiled together, hypotensive effect is more obvious.