Junior, Mid Level and Senior?
There is a very wrong idea in the market that the level of knowledge of the professional can be measured in years of experience.
I explain: a DBA that takes care of a single database, the only one in his company, for 20 years, whatever, can be compared with those who see a new database every day?
I mean, it is not the time of experience, but the amount, complexity, criticality, and size, both in bytes and in the number of users, of those databases. Add to this the projects, and the occurrence of Murphy's law (how many failures this DBA has gone through), and based on these numbers, you will be able to compare one professional to another.
When taking care of only one environment, unless it is a company with a very large park (say, 50 instances on 30 servers), the DBA will not acquire an experience comparable to those who work in a Data Center, or a consulting company, where some face an unknown problem each day.
And even in a large environment, the more stable it is, the less prepared the DBA will be for various situations, as they will be unknown to him.
When you work in just one environment, you already know many of the problems that happen (that blessed SQL command that nobody fixes, that tape drive that lives with problems), and you also know people, and they know you, which makes your work much easier than for someone outside.
Since it is not easy to make this math (only with a good interview, and with CV confirmations), a more correct way to measure the level of a professional is not for the years on the road, but for what he knows how to do.
The most important thing is not knowing how to do it, but, knowing that it is possible to be done and where are the means to do it. "J.P.S."
So, let's start from DBA Júnior.
The Junior DBA needs to know (see that this list applies easily to any database):
- Installation (but not Upgrade).
- Creation of Databases.
- Checking and changing parameters.
- Execution of scripts.
- Maintenance of users and permissions.
- Maintenance of objects (Tables, Indexes, etc.).
- Space maintenance.
- Execution of physical and logical Backup (but not Restore).
- Transport of objects between servers.
- Availability check.
- Beginning of problem checking (Troubleshooting).
- Start of performance analysis (Tuning).
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And the mid-level DBA?
The mid-level DBA must be able to do everything in the database. Of course, he still doesn't know how to do everything, because he hasn't gone through many situations yet, but he knows how to learn how to do it. He can do everything in the database, but he may need time to study and test, or even help from another mid-level (or Senior) who has been through this situation.
The mid-level DBA can perform any activity in a database, but these activities will not have the same speed, assertiveness and quality as if they were performed by a Senior DBA.
Example: the mid-level DBA may never have needed to perform an Oracle CONTROLFILE Restore, but he certainly knows that he has several options available to perform this operation, knows where to find the official documentation on it, and has a good idea of the commands he will need to execute.
He will try his first option, which may result in an error, but he will get the second one right.
There are some key areas that need to have already been executed by the mid-level DBA, at least in part: these areas are:
I mean, a mid-level DBA that has not made any Recovery, is not yet mid-level. If he has not done a RAC, but have already done a Data Guard, he is forgiven.
The more situations the mid-level DBA dominates, the closer he gets to the Senior.
And the Senior DBA?
The Senior DBA is like the mid-level DBA, although he has already gone through most of the activities he has to perform, and most importantly, he masters the four key areas (Backup & Recovery, Tuning, Troubleshooting and High Availability), and can perform them with speed, quality, assertiveness, and finally what makes he a Senior: tranquillity and few errors.
The Senior DBA also doesn't know how to do everything, but as he has already done a lot, his ability to adapt and learn is very sharp.
For example, he did not manage Oracle on HP-UX, but as he has done a lot on Linux, AIX and Solaris, his learning curve will be fast and sure.