OCA /OCP Oracle Database 11g A ll-in-One Exam Guide- P22 docx

OCA/OCP Oracle Database 11g All-in-One Exam Guide 166 Self Test 1. Which protocols can Oracle Net 11g use? (Choose all correct answers.) A. TCP B. UDP C. SPX/IPX D. SDP E. TCP with secure sockets F. Named Pipes G. LU6.2 H. NetBIOS/NetBEUI 2. Where is the division between the client and the server in the Oracle environment? (Choose the best answer.) A. Between the instance and the database B. Between the user and the user process C. Between the server process and the instance D. Between the user process and the server process E. The client-server split varies depending on the stage of the execution cycle 3. Which of the following statements about listeners is correct? (Choose the best answer.) A. A listener can connect you to one instance only. B. A listener can connect you to one service only. C. Multiple listeners can share one network interface card. D. An instance will only accept connections from the listener specified on the local_listener parameter. 4. You have decided to use Local Naming. Which files must you create on the client machine? (Choose the best answer.) A. tnsnames.ora and sqlnet.ora B. listener.ora only C. tnsnames.ora only D. listener.ora and sqlnet.ora E. None—you can rely on defaults if you are using TCP and your listener is running on port 1521 Chapter 4: Oracle Networking 167 PART I 5. If you stop your listener, what will happen to sessions that connected through it? (Choose the best answer.) A. They will continue if you have configured failover. B. They will not be affected in any way. C. They will hang until you restart the listener. D. You cannot stop a listener if it is in use. E. The sessions will error out. 6. Study this tnsnames.ora file: test = (description = (address_list = (address = (protocol = tcp)(host = serv2)(port = 1521)) ) (connect_data = (service_name = prod) ) ) prod = (description = (address_list = (address = (protocol = tcp)(host = serv1)(port = 1521)) ) (connect_data = (service_name = prod) ) ) dev = (description = (address_list = (address = (protocol = tcp)(host = serv2)(port = 1521)) ) (connect_data = (service_name = dev) ) ) Which of the following statements is correct about the connect strings test, prod, and dev? (Choose all correct answers.) A. All three are valid. B. All three can succeed only if the instances are set up for dynamic instance registration. C. The test connection will fail, because the connect string doesn’t match the service name. D. There will be a port conflict on serv2, because prod and dev try to use the same port. OCA/OCP Oracle Database 11g All-in-One Exam Guide 168 7. Consider this line from a listener.ora file: L1=(description=(address=(protocol=tcp)(host=serv1)(port=1521))) What will happen if you issue this connect string? connect scott/tiger@L1 (Choose the best answer) A. You will be connected to the instance L1. B. You will only be connected to an instance if dynamic instance registration is working. C. The connection attempt will fail. D. If you are logged on to the server machine, IPC will connect you to the local instance. E. The connection will fail if the listener is not started. 8. Which of these memory structures is not stored in the SGA for a shared server session? (Choose the best answer.) A. Cursor state B. Sort space C. Stack space 9. Match the object to the function: Object Function a. Common queue A. Connects users to dispatchers b. Dispatcher B. Stores jobs waiting for execution c. Large pool C. Executes SQL statements d. Listener D. Stores results waiting to be fetched e. Response queue E. Receives statements from user processes f. Shared server F. Stores UGAs accessed by all servers 10. Which of the following is true about dispatchers? (Choose all correct answers.) A. Dispatchers don’t handle the work of users’ requests; they only interface between user processes and queues. B. Dispatchers share a common response queue. C. Dispatchers load-balance connections between themselves. D. Listeners load-balance connections across dispatchers. E. You can terminate a dispatcher, and established sessions will continue. Chapter 4: Oracle Networking 169 PART I 11. Which of the following statements about shared servers are true? (Choose the best answer.) A. All statements in a multistatement transaction will be executed by the same server. B. If one statement updates multiple rows, the work may be shared across several servers. C. The number of shared servers is fixed by the SHARED_SERVERS parameter. D. Oracle will spawn additional shared servers on demand. Self Test Answers 1. þ A, D, E, and F. TCP, SDP, TCPS, and NMP are the supported protocols with the current release. ý B, C, G, and H. B and H are wrong because UDP and NetBIOS/NetBEUI have never been supported. C and G are wrong because SPX and LU6.2 are no longer supported. 2. þ D. The client-server split is between user process and server process. ý A, B, C, and E. These all misrepresent the client-server architecture. 3. þ C. Many listeners can shared one address, if they use different ports. ý A, B, and D. A is wrong because one listener can launch sessions against many instances. B is wrong because a listener can connect you to a registered service. D is wrong because the local_listener parameter controls which listener the instance will register with dynamically; it will also accept connections from any listener that has it statically registered. 4. þ C. This is the only required client-side file for local naming. ý A, B, D, and E. A is wrong because sqlnet.ora is not essential. B and D are wrong because they refer to server-side files. E is wrong because some configuration is always necessary for local naming (though not for Easy Connect). 5. þ B. The listener establishes connections but is not needed for their maintenance. ý A, C, D, and E. These are all incorrect because they assume that the listener is necessary for the continuance of an established session. 6. þ A and B. All three are valid but will only work if the services are registered with the listeners. ý C and D. C is wrong because there need be no connection between the alias used in a connect string and the service name. D is wrong because many services can be accessible through a single listening port. OCA/OCP Oracle Database 11g All-in-One Exam Guide 170 7. þ C. The CONNECT_DATA that specifies a SID or service is missing. ý A, B, D, and E. A is wrong because L1 is the connect string, not an instance or service name. B is wrong because dynamic registration is not enough to compensate for a missing CONNECT_DATA clause. D is wrong because the use of IPC to bypass the listener is not relevant. E is wrong because (while certainly true) it is not the main problem. 8. þ C. Stack space is not part of the UGA and therefore does not go into the SGA. ý A and B. These are UGA components and therefore do go into the SGA. 9. þ a – B, b – E, c – F, d – A, e – D, f – C These are the correct mappings of objects to functions. 10. þ A and D. Dispatchers maintain the connection to user processes, place requests on the common queue, and retrieve result sets from response queues. ý B, C, and E. B is wrong because each dispatcher has its own response queue. C is wrong because it is the listener that load-balances, not the dispatchers. E is wrong because the connections to a dispatcher are persistent: if it dies, they will be broken. 11. þ D. To prevent queueing on the common queue, Oracle will launch additional shared servers—but only up to the max_shared_servers value. ý A, B, and C. A is wrong because each statement may be picked up by a different server. B is wrong because any one statement can be executed by only one server. C is wrong because this parameter controls the number of servers initially launched, which may change later. CHAPTER 5 Oracle Storage Exam Objectives In this chapter you will learn to • 052.6.1 Work with Tablespaces and Datafiles • 052.6.2 Create and Manage Tablespaces • 052.6.3 Handle Space Management in Tablespaces 171 OCA/OCP Oracle Database 11g All-in-One Exam Guide 172 The preceding two chapters dealt with the instance and the sessions against it: processes and memory structures. This chapter begins the investigation of the database itself. All data processing occurs in memory, in the instance, but data storage occurs in the database on disk. The database consists of three file types: the controlfile, the online redo log files, and the datafiles. Data is stored in the datafiles. Users never see a physical datafile. All they see are logical segments. System administrators never see a logical segment. All they see are physical datafiles. The Oracle database provides an abstraction of logical storage from physical. This is one of the requirements of the relational database paradigm. As a DBA, you must be aware of the relationship between the logical and the physical storage. Monitoring and administering these structures, a task often described as space management, used to be a huge part of a DBA’s workload. The facilities provided in recent releases of the database can automate space management to a certain extent, and they can certainly let the DBA set up storage in ways that will reduce the maintenance workload considerably. Overview of Tablespaces and Datafiles Data is stored logically in segments (typically tables) and physically in datafiles. The tablespace entity abstracts the two: one tablespace can contain many segments and be made up of many datafiles. There is no direct relationship between a segment and a datafile. The datafiles can exist as files in a file system or (from release 10g onward) on Automatic Storage Management (ASM) devices. The Oracle Data Storage Model The separation of logical from physical storage is a necessary part of the relational database paradigm. The relational paradigm states that programmers should address only logical structures and let the database manage the mapping to physical structures. This means that physical storage can be reorganized, or the whole database moved to completely different hardware and operating system, and the application will not be aware of any change. Figure 5-1 shows the Oracle storage model sketched as an entity-relationship diagram, with the logical structures to the left and the physical structures to the right. There is one relationship drawn in as a dotted line: a many-to-many relationship between segments and datafiles. This relationship is dotted, because it shouldn’t be there. As good relational engineers, DBAs do not permit many-to-many relationships. Resolving this relationship into a normalized structure is what the storage model is all about. The following discussion takes each of the entities in Figure 5-1 one by one. The tablespace entity resolves the many-to-many relationship between segments and datafiles. One tablespace can contain many segments and be made up of many datafiles. This means that any one segment may be spread across multiple datafiles, and any one datafile may contain all of or parts of many segments. This solves many storage challenges. Some older database management systems used a one-to-one Chapter 5: Oracle Storage 173 PART I relationship between segments and files: every table or index would be stored as a separate file. This raised two dreadful problems for large systems. First, an application might well have thousands of tables and even more indexes; managing many thousands of files was an appalling task for the system administrators. Second, the maximum size of a table is limited by the maximum size of a file. Even if modern operating systems do not have any practical limits, there may well be limitations imposed by the underlying hardware environment. Use of tablespaces bypasses both these problems. Tablespaces are identified by unique names in the database. The segment entity represents any database object that stores data and therefore requires space in a tablespace. Your typical segment is a table, but there are other segment types, notably index segments (described in Chapter 7) and undo segments (described in Chapter 8). Any segment can exist in only one tablespace, but the tablespace can spread it across all the files making up the tablespace. This means that the tables’ sizes are not subject to any limitations imposed by the environment on maximum file size. As many segments can share a single tablespace, it becomes possible to have far more segments than there are datafiles. Segments are schema objects, identified by the segment name qualified with the owning schema name. Note that programmatic schema objects (such as PL/SQL procedures, views, or sequences) are not segments: they do not store data, and they exist within the data dictionary. The Oracle block is the basic unit of I/O for the database. Datafiles are formatted into Oracle blocks, which are consecutively numbered. The size of the Oracle blocks is fixed for a tablespace (generally speaking, it is the same for all tablespaces in the database); the default (with release 11g) is 8KB. A row might be only a couple hundred bytes, and so there could be many rows stored in one block, but when Logical view Tablespace Segment Extent Oracle block Operating system block Datafile Physical view Figure 5-1 The Oracle storage model OCA/OCP Oracle Database 11g All-in-One Exam Guide 174 a session wants a row, the whole block will be read from disk into the database buffer cache. Similarly, if just one column of one row has been changed in the database buffer cache, the DBWn will (eventually) write the whole block back into the datafile from which it came, overwriting the previous version. The size of an Oracle block can range from 2KB to 16KB on Linux or Windows, and to 32KB on some other operating systems. The block size is controlled by the parameter DB_BLOCK_SIZE. This can never be changed after database creation, because it is used to format the datafile(s) that make up the SYSTEM tablespace. If it becomes apparent later on that the block size is inappropriate, the only course of action is to create a new database and transfer everything into it. A block is uniquely identified by its number within a datafile. Managing space one block at a time would be a crippling task, so blocks are grouped into extents. An extent is a set of consecutively numbered Oracle blocks within one datafile. Every segment will consist of one or more extents, consecutively numbered. These extents may be in any and all of the datafiles that make up the tablespace. An extent can be identified from either the dimension of the segment (extents are consecutively numbered per segment, starting from zero) or the dimension of the datafile (every segment is in one file, starting at a certain Oracle block number). A datafile is physically made up of a number of operating system blocks. How datafiles and the operating system blocks are structured is entirely dependent on the operating system’s file system. Some file systems have well-known limitations and are therefore not widely used for modern systems (for example, the old MS-DOS FAT file system could handle files up to only 4GB, and only 512 of them per directory). Most databases will be installed on file systems with no practical limits, such as NTFS on Windows or ext3 on Linux. The alternatives to file systems for datafile storage are raw devices or Automatic Storage Management (ASM). Raw devices are now very rarely used for datafile storage because of manageability issues. ASM is detailed in Chapter 20. An operating system block is the basic unit of I/O for your file system. A process might want to read only one byte from disk, but the I/O system will have to read an operating system block. The operating system block size is configurable for some file systems (for example, when formatting an NTFS file system you can choose from 512B to 64KB), but typically system administrators leave it on default (512B for NTFS, 1KB for ext3). This is why the relationship between Oracle blocks and operating system blocks is usually one-to-many, as shown in Figure 5-1. There is no reason not to match the operating system block size to the Oracle block size if your file system lets you do this. The configuration that should always be avoided would be where the operating system blocks are bigger than the Oracle blocks. Segments, Extents, Blocks, and Rows Data is stored in segments. The data dictionary view DBA_SEGMENTS describes every segment in the database. This query shows the segment types in a simple database: Chapter 5: Oracle Storage 175 PART I SQL> select segment_type,count(1) from dba_segments group by segment_type 2 order by segment_type; SEGMENT_TYPE COUNT(1) CLUSTER 10 INDEX 3185 INDEX PARTITION 324 LOB PARTITION 7 LOBINDEX 760 LOBSEGMENT 760 NESTED TABLE 29 ROLLBACK 1 TABLE 2193 TABLE PARTITION 164 TYPE2 UNDO 10 11 rows selected. SQL> In brief, and in the order they are most likely to concern a DBA, these segments types are • TABLE These are heap-structured tables that contain rows of data. Even though a typical segment is a table segment, never forget that the table is not the same as the segment, and that there are more complex table organizations that use other segment types. • INDEX Indexes are sorted lists of key values, each with a pointer, the ROWID, to the physical location of the row. The ROWID specifies which Oracle block of which datafile the row is in, and the row number within the block. • TYPE2 UNDO These are the undo segments (no one refers to them as “type2 undo” segments) that store the pre-change versions of data that are necessary for providing transactional integrity: rollback, read consistency, and isolation. • ROLLBACK Rollback segments should not be used in normal running from release 9i onward. Release 9i introduced automatic undo management, which is based on undo segments. There will always be one rollback segment that protects the transactions used to create a database (this is necessary because at that point no undo segments exist), but it shouldn’t be used subsequently. • TABLE PARTITION A table can be divided into many partitions. If this is done, the partitions will be individual segments, and the partitioned table itself will not be a segment at all: it will exist only as the sum total of its partitions. Each table partition of a heap table is itself structured as a heap table, in its own segment. These segments can be in different tablespaces, meaning that it becomes possible to spread one table across multiple tablespaces. • INDEX PARTITION An index will by default be in one segment, but indexes can also be partitioned. If you are partitioning your tables, you will usually partition the indexes on those tables as well. . and Datafiles • 052.6.2 Create and Manage Tablespaces • 052.6.3 Handle Space Management in Tablespaces 171 OCA/ OCP Oracle Database 11g All-in-One Exam Guide 172 The preceding two chapters dealt. devices. The Oracle Data Storage Model The separation of logical from physical storage is a necessary part of the relational database paradigm. The relational paradigm states that programmers should address. block Datafile Physical view Figure 5-1 The Oracle storage model OCA/ OCP Oracle Database 11g All-in-One Exam Guide 174 a session wants a row, the whole block will be read from disk into the database buffer cache.