数据管理员面试常见七个问题
1. Why is a UNION ALL faster than a UNION?
The union operation, you will recall, brings two sets of data together. It will not, however, produce duplicate or redundant rows. To perform this feat of magic, a SORT operation is done on both tables. This is obviously computationally
intensive, and uses significant memory as well.
A UNION ALL conversely just dumps collection of both sets together in random order, not worrying about duplicates.
2. What are some advantages to using Oracle's CREATE DATABASE statement to create a new database manually?
• You can script the process to include it in a set of install scripts you deliver with a product.
• You can put your create database script in CVS for version control, so as you make changes or adjustments to it, you can track them like you do changes to software code.
• You can log the output and review it for errors.
• You learn more about the process of database creation, such as what options are available and why.
3. What are three rules of thumb to create good passwords? How would a DBA enforce those rules in Oracle? What business challenges might you encounter?
Typical password cracking software uses a dictionary in the local language, as well as a list of proper names, and combinations thereof to attempt to guess unknown passwords. Since computers can churn through tens of thousands of attempts quickly, this can be a very effective way to break into a database. A good password therefore should not be a dictionary word; it should not be a proper name, birthday, or other obvious guessable information. It should also be of sufficient length, such as eight to 10 characters, including upper and lowercase, special characters, and even alternate characters if possible.
Oracle has a facility called password security profiles. When installed they can enforce complexity, and length rules as well as other password related security measures.
In the security arena, passwords can be made better, and it is a fairly solvable problem. What about in the real world? Often the biggest challenge is in implementing a set of rules like this in the enterprise. There will likely be a lot of resistance to this, as it creates additional hassles for users of the system who may not be used to thinking about security seriously. Educating business folks about the real risks, by coming up with real stories of vulnerabilities and break-ins you've encountered on the job, or those discussed on the internet goes a long way towards emphasizing what is at stake.
4. Describe the Oracle Wait Interface, how it works, and what it provides. What are some limitations? What do the db_file_sequential_read and db_file_scattered_read events indicate?
The Oracle Wait Interface refers to Oracle's data dictionary for managing wait events. Selecting from tables such as v$system_event and v$session_event give you event totals through the life of the database (or session). The former are totals for the whole system, and latter on a per session basis. The event db_file_sequential_read refers to single block reads, and table accesses by rowid. db_file_scattered_read conversely refers to full table scans. It is so named because the blocks are read, and scattered into the buffer cache.
5. How do you return the top-N results of a query in Oracle? Why doesn't the obvious method work?
Most people think of using the ROWNUM pseudocolumn with ORDER BY. Unfortunately the ROWNUM is determined before the ORDER BY so you don't get the results you want. The answer is to use a subquery to do the ORDER BY first. For example to return the top five employees by salary: SELECT * FROM (SELECT * FROM employees ORDER BY salary) WHERE ROWNUM < 5;
6. Can Oracle's Data Guard be used on Standard Edition, and if so how? How can you test that the standby database is in sync?
Oracle's Data Guard technology is a layer of software and automation built on top of the standby database facility. In Oracle Standard Edition it is possible to be a standby database, and update it manually. Roughly, put your production database in archivelog mode. Create a hotbackup of the database and move it to the standby machine. Then create a standby controlfile on the production machine, and ship that file, along with all the archived redolog files to the standby server. Once you have all these files assembled, place them in their proper locations, recover the standby database, and you're ready to roll. From this point on, you must manually ship, and manually apply those archived redologs to stay in sync with production.
To test your standby database, make a change to a table on the production server, and commit the change. Then manually switch a logfile so those changes are archived. Manually ship the newest archived redolog file, and manually apply it on the standby database. Then open your standby database in read-only mode, and select from your changed table to verify those changes are available. Once you're done, shutdown your standby and startup again in standby mode.
7. What is a database link? What is the difference between a public and a private database link? What is a fixed user database link?
A database link allows you to make a connection with a remote database, Oracle or not, and query tables from it, even incorporating those accesses with joins to local tables.
A private database link only works for, and is accessible to the user/schema that owns it. Any user in the database can access a global one. A fixed user link specifies that you will connect to the remote db as one and only one user that is defined in the link. Alternatively, a current user database link will connect as the current user you are logged in as.
As you prepare for your DBA Interview, or prepare to give one, we hope these questions provide some new ideas and directions for your study. Keep in mind that there are a lot of directions an interview can go. As a DBA, emphasize what you know, even if it is not the direct answer to the question, and as an interviewee, allow the interview to go in creative directions.
In the end, what is important is potential or aptitude, not specific memorized answers. So listen for problem-solving ability, and thinking outside the box, and you will surely find or be the candidate for the job.
数据管理员面试常见七个问题由查字典英语网小编整理,仅供参考。
上一篇: 英语面试题:为什么喜欢这个工作
下一篇: 关于“裸辞”
国际英语资讯:Indian defense ministry signs contract for building 8 anti-submarine warfare shallow water c
体坛英语资讯:Barca look to take another step toward title on Tuesday night
体坛英语资讯:Peng Shuai advances to doubles semifinals of Kunming Tennis Open
国际英语资讯:Families of Boeing 737 MAX crash victims file suit against Boeing in Chicago
5G网络或干扰气象卫星工作
体坛英语资讯:Four things we learned from Spains Matchday 33
关于睡眠的8个流言
体坛英语资讯:Shandong Luneng beat Johor DT to top Group E in AFC Champions League
体坛英语资讯:Beitar Jerusalem defeat Atletico Madrid 2-1 in Israel friendly
国内英语资讯:Chinese defense official calls for efforts to avoid conflict at sea
国内英语资讯:Chinese team preparing to leave for trade talks in U.S.: FM spokesperson
Internet Changes our Life 网络改变我们的生活
国内英语资讯:China outlines factors for consideration in listing unreliable foreign entities
饮酒作乐已成过去 如今年轻人休假爱晒照
体坛英语资讯:Lin Dan suffers unexpected knock-out in Asian Badminton C-ships
气象学家警告:5G网络或干扰气象卫星工作
国际英语资讯:News Analysis: New Israeli elections will put Israeli-Palestinian relations at stake again
国内英语资讯:Tibet launches venture base to promote cultural industry
国内英语资讯:National rejuvenation is the common aspiration across Strait: James Soong Chu-yu
国内英语资讯:Xinhua Headlines: Worlds factory looks to non-manufacturing for leapfrog development
体坛英语资讯:China, Japan ready for face-to-face in ITTF World Championships womens singles quarterfina
国内英语资讯:China makes 3-point proposal on enhancing defense cooperation in Asia-Pacific
体坛英语资讯:Zheng Saisai advances to top 8 of Kunming Tennis Open
体坛英语资讯:Sabalenka gives Belarus early lead with Fed Cup semifinal opener win
The Joy in Library 图书馆的乐趣
国际英语资讯:U.S. police identify Virginia Beach shooter as city employee, recover more weapons
国内英语资讯:China announces guidelines to promote integrated urban-rural development
国内英语资讯:China to hold tourism promotion activities worldwide from May 15
国内英语资讯:Senior Chinese official meets ROK National Assembly Speaker
体坛英语资讯:Irans Mehrdad Mohammadi joins Portuguese Aves