Tag:count

  • Alibaba’s experience of using Flink on a large scale: how to significantly reduce HDFS pressure?

    Time:2020-3-19

    As we all know, Flink is a widely used computing engine. Flink uses checkpoint mechanism for fault tolerance [1]. Flink’s checkpoint will back up the state snapshot to the distributed storage system for subsequent recovery. The main storage we use in Alibaba is HDFS. When the number of jobs in the same cluster reaches a […]

  • SQL median function instance

    Time:2020-3-13

    Table or total sales Table: SQL statement: Copy codeThe code is as follows: SELECT * from (     SELECT a1.Name, a1.Sales, COUNT(a2.sales) Sales_Rank     FROM Total_Sales a1, Total_Sales a2     WHERE a1.Sales < a2.Sales or (a1.Sales=a2.Sales and a1.Name = a2.Name)     GROUP BY a1.Name, a1.Sales     ORDER BY a1.Sales DESC, a1.Name DESC ) as tab […]

  • Aggregation of mongodb tutorials (count, distinct, and group)

    Time:2020-2-19

    1. count: Copy codeThe code is as follows: — in an empty collection, count returns 0.     > db.test.count()     0— test the return value of count after inserting a document.     > db.test.insert({“test”:1})     > db.test.count()     1     > db.test.insert({“test”:2})     > db.test.count()     2— count, like find, accepts conditions. From the results, […]

  • Deep good article: PHP copy on write and garbage collection mechanism (transfer)

    Time:2020-2-12

    Original address: http://www.php100.com/9/20/87255.html Copy on writeCOW)It is an optimization strategy in the field of computer programming. The core idea is that if multiple callers require the same resource (such as data storage on memory or disk), they will get the same pointer to the same resource together. Until a caller tries to modify the content […]

  • PHP calendar function manual

    Time:2020-2-9

    PHP calendar function installation Function name describe cal_days_in_month Returns the days of a month in a year in a calendar cal_from_jd Convert Julian day count to a supported calendar. cal_info Returns information about the selected calendar cal_to_jd Transition from a supported calendar to Julian day count. easter_date Gets the UNIX timestamp of Easter midnight for […]

  • Redis learning note 1 – data structure

    Time:2020-2-5

    Redis is an efficient NoSQL database, which uses key value to save data and is generally used as a high-speed distributed cache. Redis key design skills Redis, as a cache, can quickly find the required data through the key, which is generally used as the cache of the database. Therefore, the key design of redis […]

  • The answer to the success of IOS interview

    Time:2020-1-31

    The answer to the following question is an article written before, “the question of success in IOS interview”. Now I have sorted out one answer to you. I hope it can help you. If you have any questions, please contact me. [email protected] 1. What are the functions of the properties readwrite, readonly, assign, retain, copy, […]

  • Thinking about block and static variable

    Time:2020-1-25

    In the recent interview, I was asked all kinds of questions. Some of them were really confused. Block calls sometimes generate circular references, andHow to dereference a loop, for IOS development, I think everyone knows. Recently, however, I was asked such a question,Does declaring static variables inside a block cause circular references?The first reaction is […]

  • Basic concept and implementation principle of Flink window

    Time:2020-1-6

    Window means window. In the flow processing system, data flows into the system continuously. We can process the incoming data one by one, or process multiple data in the flow at a time according to certain rules. When processing data, the program needs to know when to start processing and what data to process. Windows […]

  • [original] advanced IOS development (Tang Qiao) reading notes (1)

    Time:2019-12-23

    How to improve IOS development skills 1. Read the blog: https://github.com/tangqiao/iosblogcn address of more than 40 IOS development bloggers2. Reading: read a high-quality IOS development book every year3. Watch WWDC video4. Look at Apple’s official documents5. Look at the code of open source project6. Write more code, think more7. More communication with peers8, share Part […]

  • [original] advanced IOS development (Tang Qiao) reading notes (2)

    Time:2019-12-3

    Part 3: the underlying principles of IOS development 1. Objective-C object model 1.1 isa pointer Code of nsobject. H: NS_ROOT_CLASS @interface NSObject { Class isa; } Code of objc. H: typedef struct objc_class *Class; typedet struct objc_object { Class isa; } *id; Each object has a pointer named isa to the object’s class The flow […]

  • Hadoop Construction and the First Hadoop Small Project: Word Counting

    Time:2019-9-20

    Construction of Hadoop I built Hadoop on Windows 10 myself. References are as follows: 1. Detailed installation and configuration of Hadoop 2. Winutils Download 3.hadoop 3.0.3 Download 4hadoop starts error-reporting java.lang.NoClassDefFoundError:/org/apache/hadoop/yarn/server/timeline Collector Manager The first Hadoop item: word counting Word counting should be the first small entry for many people into Hadoop. My own reference […]