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Introduction and foundations

7. System Global Area Part 2

Hello everyone and welcome back. Today we will continue talking about the system global area (SGA).So today is Part part two.Let's start. In this lecture, we will learn how to understand the large pool, Java pool, fixed SGA, and streams pool, as well as how to size SGA and PG EA. I will try to make it very simple in this lecture. Now we will talk about the large pool. Actually, the large pool contains memory used by special Oracle features. When I say Oracle special features, it could be like, for example, shared server processes, and we have talked about shared server processes before, as well as, for example, parallel querying. As you can see in this example, I've chosen select, parallel, and four from EMP. Actually, we call this optimising hints. So here, Oracle will open four processes in order to execute this select statement. So the large boolean will help in this. Okay, very nice. Another important task for the large pool is that it contains memory for database backup and recovery operations and also for input and output server processes. So take it very simply and just understand these points only.We now have Java bool, streams pool, and fixed SGA as well. Let's make it simple. The Java Bowl parses Java code and scripts. As a result, it is a memory for Java code. We have streams polled, and it's memory that provides stream processes. So what is the meaning of Oracle streams? You have to do a search on this topic because it's out of the scope of this course, but it's a very big one. Just remember that streams pool to provide memory for the Oracle stream processes. In addition, we have a small memory called fixed aga that contains general information about the database and the instance's state. So I just want you to remember this simple information. Okay, now we will talk about sizing for SGA and PGA. First, let's understand the size of the SGA. I told you before that the SGA is a systemic global area and contains many memories and many areas. We have two methods for sizing the SGA. The first method is called using automatic shared memory management. ASM, it's very simple. I have two parameters. The first parameter is called SGA and is the score target. And I have SGA, underscore max, underscore the SGA, and the score target. It is the actual memory and is used by the current SGA. The maximum size of the SGA's underscore is the most memory that will be available for the SGA in the instance. So anyway, the main parameter is this one SGA target. So the database administrator sets the value for this parameter. So after the DBA entered the value for the SGA target, the Oracle database automatically distributed this memory among the various SGA components. So when you set the size for the SGA target, Oracle will make sizes for all these components, like the shared pool, the large pool, and the red log buffer. Actually, the DBA can change the system to set SGand the score target, and he will put value, as we will discuss later. I just want you to understand the concept. Now, another way uses manual shared memory management, and this needs a very expert DBA, the French DBA, who needs a lot of time to understand all these things. So most of DDBAS uses the first method, which is the automatic one, but in the manual method, you must manually configure several SGA component sizes. So how do we do it manually? First thing, the DBA should set a parameter called memory and the score target to p zero.And also, he will set another parameter called SGA and the score target to zero. Then he will manually configure the SGA component. So he will put size for the shared pool, size for thelarge pool, size for the red log buffer and so on. So I think the first method is common use andmore simple this oracle do all this job shared poolNow let's talk about the PGA. Actually, we also have two methods using automatic PGA memory management, and this is very simple. I have only one parameter called PGA underscore aggregate underscore target. What is the meaning of this parameter? It is the total amount of PGAnd memory allocated across all database server processes and packaging processes. Remember that this is an aggregated, not permanent, process for all the database processes. Okay, very nice. And Oracle strongly recommends that you leave automatic PGA memory management enabled. So Oracle told you to please don't try to do this manually. So just make it automatic. The other way is called using manual PGA memory management. Here you must manually configure several PGA component sizes, and it is not recommended. So automatically, it will be the best choice in the SGA and PGA. Okay? So just take it simple; there's no need to go deep because we will understand this more. I'll have more later on. Thank you for listening. I'll see you in the next video. Bye.

8. Background Processes

Hello everyone and welcome! We will continue talking about the database innocence, buttoday we will talk about the background processes. So, what we will learn in this lecture firstthing, we will understand the packagram processes and alsothe main purpose of each packet ground process. Now, as I told you before, that database instance contains memory and processes. We have two types of processes. We have a server process, and we also have background processes. Now, we understand what is the meaning ofserver process and we describe it in detail. Regarding the package around the processes, I have required processes and I also have optional processes. First thing, let's define the background processes. The background processes are a bunch of dedicated server-side processes running in the background. We have many tasks for the pack-ground processes. Each of these has a specific job. But the main task is writing database blocks to disk, writing redo entries to disk, making sure all the database files on disc are synchronised, and also performing maintenance tasks. Let's try to understand these processes one by one. First and foremost, we have Dbwn database writer processes. Now, when we see N, this means that I could have many database writers. Remember this. Now, the main purpose of the database writer is very simple. It is responsible for writing the contents of the database buffer to files on disk. That's it. Regarding the log writer Lgwr, it is responsible for writing redo records from the redo log buffering memory onto a physical disk. and we describe the redo log buffering in details. Remember this. Now, we have also shake point process CKPT. This process handles database check points. What is the meaning of shakes points? Actually, it's very simple. An Oracle shake point is a database event that synchronises modified data blocks in memory from the buffer cache with the data files on disk. So simply, this process synchronises the data between the buffer and the database files in the physical location. This is very nice. We have a process called the System Monitor Process. Actually, it performs recovery during the start-up sequence of the Oracle instance if required. In addition, he is in charge of removing any unused temporary segments. We will understand temporary segment later. So, this is the main purpose of the SMoon. A process monitor (PMON) performs process recovery when a user process or a session fails. So, this is the main purpose. And also, it is responsible for cleaning up any changes made to blocks in the database Buffalo cache and releasing resources that were previously used by a failed user session. So that's it. Take it like this. We will understand more and more later, but I just want you to understand the concept now. Okay, very nice. We have a process called recovery process recoil, and it's used as a part of distributed database transactions. What is the meaning of "distributed transaction"? Actually, distributed transactions are transactions that involve multiple databases. So it's very simple. I have two databases. For example, when I want to commit, the commit should happen on the two databases together. If I make a rollback, the rollback should happen on the two databases together. That's it. So this process help in this we have alsoa process called listener registrations process L reg. It is responsible for registering the Oracle instance with the Oracle Network Listener. Actually, the listener accepts remote incoming user connections. So we use the listener in order to connect to the database remotely. So this process is averagely helpful for this. That's it. We also have the RCN archival process. Remember that when ICN, this means that I may have multiple archival processes. What is the main task for archival processes? It is responsible for copying the Oracle redo log files to a remote storage device after a redo log switch has occurred. And why do we do this? Because copying the database reader logs to another storage system is very important from a backup and recovery perspective, That's it. So this is the information I want you to know today. Thank you, and I'll see you in the next video.

9. Database Files

Hello everyone and welcome back. In this lecture we will talk about the database files. We said before that the database is organised for the collection of information. It contains collections of database files stored on disk. So this is the physical, so we can see it in our eyes. Okay, actually we have nine types of files in the database. The most important are the database files, the control files, and the redo log files. And we also have other types of files. We will understand all these types of files in this lecture. Let's start first thing and themost important is the data files. Actually, it contains the actual user's data, the application data metadata, data dictionary tables, rows, exit procedures, and views. So this is the data file. Now, if you lose the data files, this means you are losing your database. The extension for the data files is "DBF database file." The second database file is called control files, and the control files store metadata about the data files and online video log files. What is the meaning of metadata about the data files? So it contains information about the data files and also the online reader log files, like the name, the locations for these database files, and the statuses. This information is required by the database instance in order to open the database. Okay? And it's very important that, if you lose the control files, you lose your database. The extension for the control file is CTL. So the control files contain metadata about the data files. The third, and also very important, are the radiolog files. And we talked about radiolog files before. So the reader log files store changes to the database as they occur and are used for data recovery. So this file contains the changes that happened to the database, like DML and DCL operations. Also, if you lose the redo logfiles, then you are losing your database. The extension for redo log files is log. Okay, we have also database backup files. It's from the name, it's very clear backup files. So it includes any backups for your database thatyou have taken and place it somewhere safe. Note it should include the data files,control files and redo log files. So we can understand that the main important files are data files, control files, and reader log files. We have also archived radiolog files, and in fact, it is a group of reader log files. So it contains an ongoing history of the data changes. So a group of redo log files equal to the archived redo log files A very important note: using the archived radiolog files and the backup files, you can recover your database. In order to understand this point, let's go to the next slide. Now I have my database. Now the clock is 8:00 a.m. I try to make a packing trip at 8:00 a.m. So I have this backup. So this pack contains data as of 08:00. Now maybe the backup will take2 hours, 3 hours, data as of 08:So remember that the backup only contains the data as of 08:00 a.m. Now, a very important note. During the backup, Oracle Database still generates the archive reading logs, which contain the changes that happen to the database. Remember this, and this is very important. Now suppose that at 10:00 I have my database crushed. So my database crashed for some reason, right? I want to restore the database. How can I back up and restore the database? So, it's very simple. To restore the database, I need the backup that I did. But this backup contains data as 08:00 only. So I have 2 hours. And in these 2 hours, a lot of transactions happened. But all these transactions are saved in the archive reader log. So I need this backup plus these archive video logs. This means that I am recovering the database 100% without losing any information. So this is the most important thing you should know about the backup files and the archived radio logs. Okay, let's continue. We have also got a parameter file. We have two types of parameter files, spphe and pfiles. Don't worry, we will understand this in detail. The parameter file defines how the database instance is configured when it starts up. So, for example, it contains parameters like, for example, PGA aggregate target. So it contains all of this critical information for the example. Now, a very important note. The SP file is a binary file you cannot edit directly. It should be through Oracle commands. So if you use the SP-5, there is no issue. You can recreate it again. But it's always better to back up the SP file always.We'll go over the SP and.p files later. Don't worry. So it is a very important file. in order for the instance to be configured. Now we have a password file. The password file stores passwords for users with administrative privileges, like the sys user. And the SYS user has the highest privilege. Remember this. But the question is, why do I have this password file? Okay? DBA passwords cannot be stored in the database because Oracle cannot access the database before innocency is started. Therefore, the authentication of the DBA must happen outside the database. Also, we have an alert log file. And this is a chronological log of messages and errors written by an Oracle database. When I say "chronological," this means "sequential," so it's a sequential order. So it contains messages and errors. So this is your go-to file in case you are trying to troubleshoot a problem with your database. For example, the alert log file contains information about when the database was started and stopped. Besides that, it contains a lot of information that will help you troubleshoot any problem. And finally, we have the trace file. In reality, each server and packing ground writes to a trace file. So when a process detects an internal error, it writes information about the error to the SRTRACE file. So these are all the types of files in the database. Don't worry; we will go more to the letter in the practical sections. So thank you for listening, and I'll see you in the next video.

10. Logical Storage Structure

Hello everyone and welcome! In this lecture we will talk about logical storage structures. Actually, we will take only one slide today, and this slide is very important. This lecture is one of the most important lectures in this course. First thing, the storage structure in Oracle contains both logical and physical elements. The physical structure is very simple. Do the data exist in data files? Okay. The data file should exist in a storage system; we have many types of storage systems and some storage area networks. We have Nas network-attached storage, we have NFS network file systems, we have ASM, which is an automatic storage management system, and also we have Exadata and file systems. There is no need to know about the storage system because this is outside the scope of the responsibilities of the database administrator; we have some people who are specialists in the storage system and also network people, so don't care about this subject. When I say physical, this means that I can see it in my eyes, so you can see the datafiles inside the Oracle server, but Oracle manages this data in a logical structure I have Oracle data blocks, and I also have extended segment table space. So now let's understand this one by one. First, the Oracle data block (oracle data stored in database blocks) is actually one block equal to 8 KB by default, and you can change this depending on whether a single Oracle database contains one or more rows. So this is the basic storage unit in logical storage. Very nice. So now we have the extent as well. What is the meaning of extent? An extent is a set of contiguous Oracle data blocks. Okay, why do we have a degree? Because it is much more efficient when allocating spaces, a collection of contiguous blocks is equal to OK, the next level of storage is segments. A segment is a set of extents. One or more extents are located for certain logical structures inside the database, for example tables and indexes. So when you are creating a table inside the database, this means you are creating segments. So one table equals one segment; one index equals one segment. That's it. And also, the container for these segments exists inside a table space. So the table space is a logical storage group that can be used to store logical database constructs such as tables and indexes. So actually, the table space logically stores the database files. As you can see, the relationship between the data file and the table space is many to one. So I could have many datafiles in one table space. So that's it. I have a block extend segment table space, and the relationship between the data file and table space is one to one, and the database can have many table spaces. In the next lecture, we will learn more about table spaces and the different types of table spaces, and we will dive into the practical. Thank you for listening. I'll see you in the next video. Bye.

11. Default tablespaces

Hello everyone and welcome back. In the previous lecture, we talked about the storage structure in the Oracle database. We said that we have physical structure and logical structure. And also, we said that in the physical world, we can see the data files. And I told you that the data files and table space have many to one relationships. So we could have many datafiles related to one table space. And the table space is the container for the segment, and the segment is any object in the database like a table or index. Table spaces and databases have a one-to-many relationship. So we could have many tablespaces belonging to one database. Now, let's understand the types of table spaces. Actually, we have many types of table spaces. We have system table space and we have sysaxtable space and temp tablespace and do and users. So this is the default table spaces in Oracle. Now let's understand it one by one, and we will take only general information for these table spaces. And this knowledge will come in handy later on in the practical. So now let's start with the system table space. Actually, the system table is used for core functionality. It stores the data dictionary, and the data dictionary is metadata, which means data about data. Remember that the data dictionary belongs to Sys Schema, and we will understand this letter in detail. Now, a very important note. Oracle creates system table space automatically when the database is created. You cannot rename or drop the system table space. So this table space belongs to Oracle's database. Okay, we don't create user data in this table space. Okay, we have CSOC table space. CSOX tablespace is actually a helper for the table space system. So the CSOX table space is an auxiliary table space to the system table space. It reduces the load on the system's table space. So it helped the system's table space. So Allah created this table space automatically when the database was created. And also, you cannot rename or drop that; you waste table space. We have also temp table spaceand this is very important. are used to manage space for database sort and joining operations and for storing global temporary tables. Other SQL operations that may require disc sorting are create, index, analyze, select, distinctgroup by ordering by, union, intersect, and minus. Let me describe this more for you. Now, for example, when you create a selected statement or execute a selected statement and this selected statement contains order by, Oracle needs a space in order to execute this statement and make an order for the selected statement, then give you the result. So all I can do is use the templatetable space in order to do this. Now maybe you will ask me why we don't use this in the PGA. For example, the program's global area memory. Okay, a good question. Because this operation could consume a large amount of RAM and space, Oracle prefers to perform it on a temporary tablespace. Okay? That's it. We also have the unfinished table space. The undo table space is used to rollback or undo changes to the database. For example, roll packet transactions. When a rollbacket statement is issued, recoverthe database and provide read consistency. I will give you examples. Suppose that the user makes an updated statement, okay? And the user still didn't make any commits. So actually, Oracle keeps the old values in this table space in order to recover them. If the user calls back, other users will read the data that was not committed from the undo table space. And this is a provide read consistency because the user,maybe he will commit or maybe he will not commit. So that's why we use the "undo" table space. And also, we have the user's table space, and this table space stores user objects and data. So here we create the tables and insert the data and the application data. So this is the user's table space. So every database should have a table space for payment user data that is assigned to users. Otherwise, user objects will be created in the systemtable space, which is not a good practice. Okay, very nice. So in the preconfigured database, users is designed as the default table space for all new users. Okay, so if you create a user and you don't mention a table space for this user, Oracle will give it the default, which is the user's table space. Okay, very nice. a very important note. All these table spaces exist in the container database and also in the blogger bill databases. We will understand what is meant by "container" and the "blogger bill" in the next lecture, don't worry. Okay, very nice. So thank you for listening, and I'll see you in the next video.

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