[20171128]rman Input or output Memory Buffers.txt --//Input Memory Buffers如何测试,不清楚.不过找到一本电子书.摘要如下: Oracle RMAN 11g Backup and Recovery.pdf 作者:Robert G. Freeman Matthew Hart 页数:689 出版社:Mc graw hill 出版号: ISBN: 978-0-07-162861-7         MHID: 0-07-162861-4 RMAN in Memory P80     RMAN builds buffers in memory through which it streams data blocks for potential backup. This memory utilization counts against the total size of the PGA and, sometimes, the SGA. There are two kinds of memory buffers. Input buffers are the buffers that are filled with data blocks read from files that are being backed up. Output buffers are the buffers that are filled when the memory-to-memory write occurs to determine whether a particular block needs to be backed up. When the output buffer is filled, it is written to the backup location. The memory buffers differ depending on whether you are backing up to or restoring from disk or tape. Figure 2-3 illustrates input and output buffer allocation. It illustrates a backup of two datafiles being multiplexed into a single backup set.          Input Memory Buffers     When you are backing up the database, the size and number of input memory buffers depend on the exact backup command being executed. Primarily, they depend on the number of files being multiplexed into a single backup. Multiplexing refers to the number of files that will have their blocks backed up to the same backup piece. To keep the memory allocation within reason, the following rules are applied to the memory buffer sizes based on the number of files being backed up together: ■ If the number of files going into the backup set is four or less, then RMAN allocates four    buffers per file at 1MB per buffer. The total will be 16MB or less. ■ If the number of files going into the backup set is greater than four, but no greater than    eight, then each file gets four buffers, each of 512KB. This ensures that the total remains    at 16MB or less. ■ If the number of files being multiplexed is greater than eight, then RMAN allocates four    buffers of size 128KB. This ensures that each file being backed up will account for 512KB    of buffer memory.     Bear in mind that these memory amounts are on a per-channel basis. So, if you allocate two channels to back up a database with 32 datafiles, for instance, then RMAN will load-balance the files between the two channels and may not end up with 16 files per channel. If some files are significantly larger than others, you may end up with only 8 files going into one backup set and 24 files going into the other. If this were the case, then the buffers for the first channel with 8 files would allocate 16MB of memory for input buffers (four buffers multiplied by 512KB each, multiplied by 8 files), and the second channel would allocate 12MB of memory buffers (512KB per file multiplied by 24 files).     You can use the following query to monitor the size of buffers on a per-file basis while the backup is running: SELECT set_count, device_type, type, filename, buffer_size, buffer_count, open_time, close_time   FROM v$backup_async_io  ORDER BY set_count, type, open_time, close_time; --//注意:原来有这个问题!下次备份注意看buffer_size! Output Buffers When Backing Up to Disk P81     In addition to input buffers, RMAN allocates output buffers, depending on what the output source is. If you are backing up to disk, then RMAN allocates output buffers that must fill up with data blocks from the input buffers before being flushed to the backup piece on your file system. Per channel, there will be four output buffers, each of which is 1MB. So, the memory footprint per channel will always be 4MB. Output Memory Buffers When Backing Up to Tape P81     Memory allocation is different when backing up to tape, to account for the slower I/O rates that we expect from tape devices. When you are backing up to or restoring from tape, RMAN allocates four buffers per channel process, each of which is 256KB, so that the total memory footprint per channel is 1MB. --//这也和我前面的测试一样,我使用as copy备份,单个数据文件每个通道4个输出缓存,而每个缓存1M,一个通道是4M.