The basic compression level for RMAN has a good compression ratio for most scenarios. commands:RMAN> The message resembles the following: The large pool is used for RMAN and for other purposes, so its total size must accommodate all uses. pieces is the I/O; either while reading from the source of the Backup encryption is explained in "Encrypting RMAN Backups". Figure 23-2 Phases of a Multichannel Backup to Tape. dbf file, an archived redo log or an RMAN "backup set". For image copies, the total number of blocks in the file. You can improve backup performance by adjusting the level of multiplexing, which is number of input files simultaneously read and then written into the same RMAN backup piece. The RMAN-specific factors affecting the SBT write phase are analogous to the factors affecting disk reads. which is shared by all the administrators. Adjust settings in the media management software. Each server session performing a backup or restore job reports its progress compared to the total work required for a job step. Consulting StaffConsulting This chapter contains the following topics: Basic Concepts of RMAN Performance Tuning, Using V$ Views to Diagnose RMAN Performance Problems. Support, SQL TuningSecurityOracle

If you enabled the Oracle Advanced Compression option, there are several different levels to choose from that provide tradeoffs between compression ratios and required CPU resources. configure backup optimization on; Although the shared pool may be unable to satisfy this memory request, the large pool can do so. The meaning of this column depends on the type of operation described by this row: For image copies, the number of blocks that have been read, For backup input rows, the number of blocks that have been read from the files being backed up, For backup output rows, the number of blocks that have been written to the backup piece, For restores, the number of blocks that have been processed to the files that are being restored in this one job step, For proxy copies, the number of files that have been copied. device. If the time for the BACKUP VALIDATE to tape is significantly less than the time for a real backup to tape, then writing to the output device is the likely bottleneck.

Compression may cause the EFFECTIVE_BYTES_PER_SECOND to be greater than the speed of real I/O. A channel writes the blocks from output buffers to storage media. RMAN can read the data from multiple sources as well. Short waits are the number of times the backup or restore process made an operating system call to poll for I/O completion in a nonblocking mode. If the database cannot get enough memory, then it obtains I/O buffer memory from the PGA and writes a message to the alert.log file indicating that synchronous I/O is used for this backup. means is that it is possible for RMAN to read two datafiles at the The block size is the amount of data written by media management software to a tape in one write operation. If EFFECTIVE_BYTES_PER_SECOND is less than the raw capacity of the hardware, then the tape is not streaming.

Binary compression is explained in "About Binary Compression for RMAN Backup Sets" and in "Making Compressed Backups". In this case, RMAN must be able to read disks with a throughput of more than 12 megabytes per second or the disk becomes the bottleneck for the backup. For proxy copies, the total number of files to be copied in this job step. RMAN> configure backup optimization off; Detail rows are updated with every buffer that is read or written during the backup step, so their granularity of update is small. Another parameter which is a If you set the initialization parameter BACKUP_TAPE_IO_SLAVES=true, then RMAN allocates tape buffers from the SGA. The number of buffers remains fixed to 16 and a size of 1 MB with You can execute an ALTER SYSTEM SET statement to set the parameter dynamically. Here ApplicationsOracle When restoring data, a channel performs these steps in reverse order and reverses the reading and writing operations. servicesApplication If this value is not large enough, then an error is recorded in the alert log, the database does not try to get buffers from the shared pool, and asynchronous I/O is not used. If the database cannot get enough memory, then it obtains I/O buffer memory from the Program Global Area (PGA) and writes a message to the alert.log file indicating that synchronous I/O is used for this backup. same time and then write them to an output device in the form of a are some of the main features of the RMAN configure backup buffers and also decides the size of the allocated memory buffer. backed up to the allocated device type. Because such drives can write data at only one speed, when they run out of data to write to tape, the tape must slow and stop. The formula for setting LARGE_POOL_SIZE is as follows: Oracle Database Concepts for more information about the large pool, and Oracle Database Reference for complete information about initialization parameters. This increases the rate at which RMAN fills tape buffers, which makes it more likely that buffers are sent to the media manager fast enough to maintain streaming. Anyone RMAN> The number of channels available for use with a device determines whether RMAN can read from and write to this device in parallel. Buy better, more expensive shoes? BACKUP VALIDATE of a backup to tape performs the same disk reads as a real backup but performs no tape I/O. The following table makes recommendations for adjusting the level of multiplexing. experience!

PortalApp Question: I need to know if Oracle RMAN is Therefore, when RMAN uses disk, the number of channels must be equal to the number of physical disks accessed.

If RMAN is backing up files to ASM, then increase the number of channels. To determine the rate of asynchronous I/O: The simplest way to identify the bottleneck is to find the data file that has the largest ratio for LONG_WAITS divided by IO_COUNT. "About Multiplexed RMAN Backup Sets" to learn how the MAXOPENFILES and FILESPERSET settings affect the level of multiplexing, "About RMAN Incremental Backups" for a conceptual overview. Short waits are the number of times the backup or restore process made an operating system call to poll for I/O completion in a nonblocking mode. Detail rows describe the files being processed by one job step, whereas aggregate rows describe the files processed by all job steps in an RMAN command. The Oracle of The database takes advantage of this feature if it is available. If RMAN is backing up to tape, then try the following adjustments: Use the PARMS and BLKSIZE parameters of the ALLOCATE CHANNEL or CONFIGURE CHANNEL command to set the size. The principal factor affecting the write phase for disk is the buffer size. MAXOPENFILES is set to 4 and FILESPERSET is set to 4. If there are not many changed blocks, RMAN may not fill output buffers fast enough to keep the tape drive streaming. If the backup uses the basic compression algorithm, then consider using the Oracle Advanced Compression option. Start RMAN and connect to the target database and recovery catalog (if used). Performance Tuning Database Support Configuring the large pool prevents RMAN from competing with other subsystems for the same memory. Often, finding the solution to a slow backup is a process of trial and error.

For all other rows except proxy copy (which does not update this column), the value is 1. DBA performance tuning consulting professionals. documentation was created as a support and Oracle training reference for use by our Ion It is possible to make RMAN take a backup of multiple terabytes of oracle databases The considerations for backup tuning change depending on whether you manage database files with ASM. To determine whether your tape is streaming when the I/O is synchronous, query the EFFECTIVE_BYTES_PER_SECOND column in the V$BACKUP_SYNC_IO or V$BACKUP_ASYNC_IO view. For backup output rows, this value is 2. When writing to disk, you can make use of disk I/O slaves just as when reading from disk. to the number of the disks within the disk group. If RMAN is backing up files to a disk-based output destination striped over multiple disks, then you can allocate multiple channels. SQL Tuning The Definitive Reference", In order to back up the flash recovery area itself using off;When you turn on backup The channel process composes a tape buffer. configure backup optimization on; RMAN> Figure 23-1 Phases of a Multichannel Backup to Disk. The server session serial number. What would you do Table 23-2 Columns of V$SESSION_LONGOPS Relevant for RMAN, The server session ID corresponding to an RMAN channel. As explained in "RATE Channel Parameter", the RATE parameter on a channel is intended to reduce, rather than increase, backup throughput so that more disk bandwidth is available for other database operations. The physical tape block size can affect backup performance. backup optimization on command: Also see PricesHelp Description of "Figure 23-1 Phases of a Multichannel Backup to Disk", Description of "Figure 23-2 Phases of a Multichannel Backup to Tape", Description of "Figure 23-3 Disk Buffer Allocation", About Binary Compression for RMAN Backup Sets, Description of "Figure 23-4 Allocation of Tape Buffers", Description of "Figure 23-5 Synchronous Tape I/O", Description of "Figure 23-6 Asynchronous Tape I/O", Monitoring RMAN Interaction with the Media Manager, Making and Updating RMAN Incremental Backups, Configuring the Backup Encryption Algorithm. The RMAN channel allocates 16 buffers of size 1 megabyte (MB) so that the total buffer size for all the input files is 16 MB.

SupportAnalysisDesignImplementationOracle The slowest of these phases in any RMAN job is called the bottleneck. If the database is on one host, but the output tape drive is attached to a different host, then Oracle Secure Backup manages the data transfer over the network. to optimize this situation? See "Tuning the Copy and Write Phases". Otherwise, the shared pool is used. optimization on command: Also, the RMAN If the rate is lower than the rate that the device specifies, then consider tuning this aspect of the backup and restore process. Asynchronous I/O to tape is simulated by using tape slaves. backup or writing the same to the target device, it is I/O all The defaults of filesperset and RMAN allocates the tape buffers in the System Global Area (SGA) or the Program Global Area (PGA), depending on whether I/O slaves are used. If and only if your disk does not support asynchronous I/O, then set DBWR_IO_SLAVES. To determine the rate of synchronous I/O: If you see data in V$BACKUP_SYNC_IO, then the problem is that you have not enabled asynchronous I/O or you are not using disk I/O slaves. Tape devices can only be accessed by one process at a time, so RMAN starts as many slaves as necessary for the number of tape devices.

This includes the following tasks: Using Backup Validation To Distinguish Between Read and Write Bottlenecks. This parameter prevents RMAN I/O buffers from competing with the library cache for SGA memory. Aggregate rows are updated when each job step completes, so their granularity of update is large. Some media manager settings, including the tape block size, may affect backup performance. As explained in "Synchronous and Asynchronous Disk I/O", some operating systems support native asynchronous I/O. The upper limit of your backup performance should be the aggregate transfer rate of all of your tape drives. Validation is explained in Validating Database Files and Backups Typically, this processing is not CPU-intensive. Oracle Backup multiplexing is RMAN's ability to read several files in a backup simultaneously from different sources and then write them to a single backup piece.

If asynchronous I/O is disabled, then RMAN allocates four backup disk I/O slaves for any nonzero value of DBWR_IO_SLAVES. The simplest way to identify the bottleneck is to query V$BACKUP_ASYNC_IO for the datafile that has the largest ratio for LONG_WAITS divided by IO_COUNT. Thus, a backup to tape involves the interaction of both RMAN and the media manager. essentially be reading the information from the source of the media. If you see data in V$BACKUP_SYNC_IO, then the problem is that you have not enabled asynchronous I/O or you are not using disk I/O slaves. dba actually impact the performance. In this way, you increase the rate at which RMAN fills tape buffers, which makes it more likely that buffers are sent to the media manager fast enough to maintain streaming. In particular, if tape drives are not locally attached to the node of the database being backed up, then incremental backups can be faster. V$BACKUP_ASYNC_IO contains rows when the I/O is asynchronous. A channel copies blocks from input buffers to output buffers and performs additional processing on the blocks. You can choose which compression algorithm RMAN uses for backups. For example, you can use the following query: If you have synchronous I/O but you set BACKUP_DISK_IO_SLAVES, then the I/O is displayed in V$BACKUP_ASYNC_IO. If the media manager compression is efficient, then it is usually the better choice. The read phase of RMAN is the phase which can be really Oracle forum. When reading from an ASM disk group, use asynchronous disk I/O if possible. When performing binary compression, RMAN applies a compression algorithm to the data in backup sets. ForumClass Remote DBA Services Feel free to ask questions on our Note: configure backup optimization on; RMAN> configure backup optimization

This is governed primarily by the filesperset You can use the V$BACKUP_SYNC_IO and V$BACKUP_ASYNC_IO views to determine the source of backup or restore bottlenecks and to see detailed progress of backup jobs. RMAN offers three modes of encryption: transparent, password-protected, and dual-mode. For example, during an incremental backup, RMAN only backs up blocks changed since a previous datafile backup as part of the same strategy. The memory from the large pool is used for many features, including the shared server, parallel query, and RMAN I/O slave buffers. The work of each channel, whether of type disk or System Backup Tape (SBT), is subdivided into the following distinct phases: A channel reads blocks from disk into input I/O buffers.

Table 23-2 describes the columns in V$SESSION_LONGOPS that are most relevant for RMAN. When the disk I/O is synchronous, a server process can perform only one task at a time. into the memory area from where it is written out to the output system is minimal and with a planned multiplexing rate, backup TuningEmergency The tape slave process executes media manager code that processes the tape buffer and internalizes it so that the media manager can process it. RMAN uses two types of rows in V$SESSION_LONGOPS: detail rows and aggregate rows. Oracle Database Reference for descriptions of the V$BACKUP_SYNC_IO and V$BACKUP_ASYNC_IO views. ASM is one example of a destination striped over multiple disks. Also, if a channel reads from a raw device managed with a volume manager, then asynchronous disk I/O also works well. When attempting to get shared buffers for I/O slaves, the database does the following: If the LARGE_POOL_SIZE initialization parameter is set, and if the DBWR_IO_SLAVES parameter is set to a nonzero value, then the database attempts to get memory from the large pool. Tape streaming during write operations has a major effect on tape backup performance.

Server There are several tasks that you can perform to identify and remedy bottlenecks that affect backup performance. In particular, if RMAN is sending data blocks to the tape drive fast enough to support streaming, but the tape is not streaming, then the SBT write phase is the bottleneck. The purpose of RMAN tuning is to identify the bottlenecks for a given job and use RMAN commands, initialization parameters, or adjustments to physical media to improve performance. ServerOracle ConceptsSoftware SupportRemote No, it is not the shoes but the traffic on the road which is causing Since the memory buffers are allocated This setting enables the database writer processes to use slaves. In this case, each allocated channel corresponds to a server process, which in the explanation that follows is identified as a channel process.
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