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1. What is a pattern? Patterns, that is, pattern. In fact, is to solve a certain type of problem methodology. You have summed up the method of solving some kind of problem to the theoretical height, that is the pattern. The classi

is not used For example, a table with a very small amount of data Under what circumstances is it not recommended to use an index?1) fields with poor data uniqueness (only a few values in a field) do not use the index For example, gender, there are only two possible data. This means that

What this article brings to you is about what is BFC? What is the use of BFC in CSS? , there is a certain reference value, the need for friends can refer to, I hope you have some help.

There is no doubt that the Linux kernel needs to manage all the hardware devices connected to the computer. If you want to manage these devices, you need to communicate with them first, there are generally two scenarios for this functionality:1. Polling (polling) allows the kernel to periodically query the status of the device, and then make the corresponding processing;2. Interrupt (interrupt) allows the h

What is a data warehouse, and what is the difference between a databaseDataWarehouseis a subject-oriented (Subject oriented), integrated (integrate), A relatively stable (non-volatile), data collection that reflects historical changes (timeVariant) to support management decisions. (

The relational database relies on the primary key, which is the cornerstone of the database physical pattern. There are only two uses of the primary key at the physical level: Uniquely identifies a row. As an object that can be effectively referenced by a foreign key. An index is a special kind of file (an index on a InnoDB data table is an inte

static void Main (string[] args) {Permute ("abc");}public static void Permute (String str) {char[] Strarray = Str.tochararray ();Permute (strarray, 0, strarray.length–1);}public static void Permute (char[] list, int. Low, int.) {int i;if (low = = high) {String cout = "";for (i = 0; I cout + = List[i];System.out.println (cout);} else {for (i = low, I Char temp = List[low];List[low] = List[i];List[i] = temp;Permute (list, low +

the flexibility of transaction management,DmProvides a set save point (SavePoint) statement and rollback to the Save point languageSentenceSave points provide a flexible rollback,Transactions can be rolled back to a savepoint during execution.Before the Save pointOperation is valid, and subsequent operations are rolled back.DmAlso have the above4Properties: atomicity, consistency, isolation, and persistence.2.Inconsistencies in concurrency and dataIf

adaptation work are divided into several classes based on the timeline, they can be divided into the following elements: precise positioning of delivery; stability and ease of use of delivery; delivery scalability; post-delivery upgrade; post-delivery service. Classification is just to express what needs to be done, and in actual operation, these elements do not have clear logical boundaries between each o

port can be divided into 3 main categories:1) Accepted ports (well known Ports): from 0 to 1023, they are tightly bound to some services. Usually the communication of these ports clearly indicates the protocol of some kind of service. For example: Port 80 is actually always HTTP traffic.2 registration port (registered Ports): from 1024 to 49151. They are loosely bound to some services. This means that ther

Topic comments This topic belongs to JavaScript more difficult to understand the knowledge point, the knowledge is also very abstract abstruse, belong to the JavaScript object-oriented thinking category, if there is no object-oriented programming thinking students, must be stumped, even if there is some OOP students to answer it

1, Kafka is what. Kafka, a distributed publish/subscribe-based messaging system developed by LinkedIn, is written in Scala and is widely used for horizontal scaling and high throughput rates. 2. Create a background Kafka is a mes

to UCS-4 is simply preceded by a 2 byte 0. UCS-4 is primarily used to save auxiliary planes, such as the second auxiliary plane in Unicode 4.0 20000-20fff-21000-21fff-22000-22fff-23000-23fff-24000-24fff-25000-25fff-26000-26fff-27000-27fff-28000-28 Fff-29000-29fff-2a000-2afff-2f000-2ffff A total of 16 auxiliary planes were added, extending from the original 65,536 encodings to nearly

the efficiency.But between security and efficiency, the first thing to consider is security. The premise of synchronization one, multiple threads to perform the time required synchronization, if it is a single thread does not need synchronization. More than one thread is using the same lock during execution. If it is,

redundancy and is not conducive to maintenance.3. How to linkLinking refers to the use of HTML header tags to introduce external CSS files.Example:head> link rel="stylesheet" type="text/css" href="style.css">head>This is the most common and recommended way to introduce CSS. In this way, all CSS code exists only in a separate CSS file, so it has good maintainability. And all the CSS code exists only in