环境：Oracle 10.2.0.5 现象：RMAN分配多个通道，但实际无法使用到并行。 构建测试用例： create tablespace dbs_d_test; alter tablespace dbs_d_test add datafile; --这里是11 alter tablespace dbs_d_test add datafile; --这里是12 alter tablespace dbs_d_test add datafile; --这里是13 alter database datafile 11,12,13 resize 1G; 1.RMAN多通道但未用到并行 2.备份语句改写使用到并行 3.备份方式改变提高效率 1.RMAN多通道但未用到并行 使用RMAN备份 run { allocate channel c1 device type disk; allocate channel c2 device type disk; allocate channel c3 device type disk; backup as copy datafile 11 format '/tmp/incr/copy11.bak'; backup as copy datafile 12 format '/tmp/incr/copy12.bak'; backup as copy datafile 13 format '/tmp/incr/copy13.bak'; release channel c1; release channel c2; release channel c3; } 使用下面SQL查询长操作： select inst_id, sid, username, opname, target, sofar, totalwork, sofar * 100 / totalwork from gv$session_longops where sofar < totalwork; 发现上面这种备份写法，虽然分配了多个通道，但实际观察并没有使用到并行。3个文件的备份是串行操作的。这点从上面的长操作中可以看到，同时从RMAN输出日志中同样也可以看到： RMAN> run { 2> allocate channel c1 device type disk; 3> allocate channel c2 device type disk; 4> allocate channel c3 device type disk; 5> 6> backup as copy datafile 11 format '/tmp/incr/copy11.bak'; 7> backup as copy datafile 12 format '/tmp/incr/copy12.bak'; 8> backup as copy datafile 13 format '/tmp/incr/copy13.bak'; 9> 10> release channel c1; 11> release channel c2; 12> release channel c3; 13> } using target database control file instead of recovery catalog allocated channel: c1 channel c1: sid=128 instance=jy1 devtype=DISK allocated channel: c2 channel c2: sid=117 instance=jy1 devtype=DISK allocated channel: c3 channel c3: sid=129 instance=jy1 devtype=DISK Starting backup at 29-AUG-18 channel c1: starting datafile copy input datafile fno=00011 name=+ZHAOJINGYU/jy/datafile/dbs_d_test.615.985387387 output filename=/tmp/incr/copy11.bak tag=TAG20180829T002101 recid=13 stamp=985393279 channel c1: datafile copy complete, elapsed time: 00:00:25 Finished backup at 29-AUG-18 Starting backup at 29-AUG-18 channel c1: starting datafile copy input datafile fno=00012 name=+ZHAOJINGYU/jy/datafile/dbs_d_test.613.985387391 output filename=/tmp/incr/copy12.bak tag=TAG20180829T002127 recid=14 stamp=985393305 channel c1: datafile copy complete, elapsed time: 00:00:25 Finished backup at 29-AUG-18 Starting backup at 29-AUG-18 channel c1: starting datafile copy input datafile fno=00013 name=+ZHAOJINGYU/jy/datafile/dbs_d_test.611.985387395 output filename=/tmp/incr/copy13.bak tag=TAG20180829T002153 recid=15 stamp=985393330 channel c1: datafile copy complete, elapsed time: 00:00:25 Finished backup at 29-AUG-18 released channel: c1 released channel: c2 released channel: c3 实际是串行操作，都是用的通道c1，这3个数据文件的copy备份消耗3个25s=75s。 2.备份语句改写使用到并行 改进写法，用到了并行： run { allocate channel c1 device type disk; allocate channel c2 device type disk; allocate channel c3 device type disk; backup as copy datafile 11,12,13 format '/tmp/incr/copy_%u.bak'; release channel c1; release channel c2; release channel c3; } 从日志看到： RMAN> run { 2> allocate channel c1 device type disk; 3> allocate channel c2 device type disk; 4> allocate channel c3 device type disk; 5> 6> backup as copy datafile 11,12,13 format '/tmp/incr/copy_%u.bak'; 7> 8> release channel c1; 9> release channel c2; 10> release channel c3; 11> } using target database control file instead of recovery catalog allocated channel: c1 channel c1: sid=129 instance=jy1 devtype=DISK allocated channel: c2 channel c2: sid=127 instance=jy1 devtype=DISK allocated channel: c3 channel c3: sid=119 instance=jy1 devtype=DISK Starting backup at 29-AUG-18 channel c1: starting datafile copy input datafile fno=00011 name=+ZHAOJINGYU/jy/datafile/dbs_d_test.615.985387387 channel c2: starting datafile copy input datafile fno=00012 name=+ZHAOJINGYU/jy/datafile/dbs_d_test.613.985387391 channel c3: starting datafile copy input datafile fno=00013 name=+ZHAOJINGYU/jy/datafile/dbs_d_test.611.985387395 output filename=/tmp/incr/copy_14tbnq76.bak tag=TAG20180829T002302 recid=16 stamp=985393432 channel c1: datafile copy complete, elapsed time: 00:00:55 output filename=/tmp/incr/copy_15tbnq76.bak tag=TAG20180829T002302 recid=17 stamp=985393432 channel c2: datafile copy complete, elapsed time: 00:00:55 output filename=/tmp/incr/copy_16tbnq76.bak tag=TAG20180829T002302 recid=18 stamp=985393435 channel c3: datafile copy complete, elapsed time: 00:00:55 Finished backup at 29-AUG-18 released channel: c1 released channel: c2 released channel: c3 实际是并行操作，分别用的通道c1、c2、c3，这3个数据文件的copy备份消耗1个55s=55s。 那为什么并行没有成倍增加效率？跟上一篇提到的一样，系统的整体I/O能力达到瓶颈了。所以一味的增加并行度并不总是有意义的。 3.备份方式改变提高效率 如果数据文件很大，但实际使用的并不多，则可以考虑使用备份集的方式，减少备份对空间的占用，一般同时也会加快备份的速度： run { allocate channel c1 device type disk; allocate channel c2 device type disk; allocate channel c3 device type disk; backup as compressed backupset datafile 11,12,13 format '/tmp/incr/datafile_%u.bak'; release channel c1; release channel c2; release channel c3; } 从日志可以看到： RMAN> run { 2> allocate channel c1 device type disk; 3> allocate channel c2 device type disk; 4> allocate channel c3 device type disk; 5> 6> backup as compressed backupset datafile 11,12,13 format '/tmp/incr/datafile_%u.bak'; 7> 8> release channel c1; 9> release channel c2; 10> release channel c3; 11> } using target database control file instead of recovery catalog allocated channel: c1 channel c1: sid=128 instance=jy1 devtype=DISK allocated channel: c2 channel c2: sid=134 instance=jy1 devtype=DISK allocated channel: c3 channel c3: sid=116 instance=jy1 devtype=DISK Starting backup at 29-AUG-18 channel c1: starting compressed full datafile backupset channel c1: specifying datafile(s) in backupset input datafile fno=00011 name=+ZHAOJINGYU/jy/datafile/dbs_d_test.615.985387387 channel c1: starting piece 1 at 29-AUG-18 channel c2: starting compressed full datafile backupset channel c2: specifying datafile(s) in backupset input datafile fno=00012 name=+ZHAOJINGYU/jy/datafile/dbs_d_test.613.985387391 channel c2: starting piece 1 at 29-AUG-18 channel c3: starting compressed full datafile backupset channel c3: specifying datafile(s) in backupset input datafile fno=00013 name=+ZHAOJINGYU/jy/datafile/dbs_d_test.611.985387395 channel c3: starting piece 1 at 29-AUG-18 channel c1: finished piece 1 at 29-AUG-18 piece handle=/tmp/incr/datafile_17tbnqi9.bak tag=TAG20180829T002857 comment=NONE channel c1: backup set complete, elapsed time: 00:00:02 channel c3: finished piece 1 at 29-AUG-18 piece handle=/tmp/incr/datafile_19tbnqia.bak tag=TAG20180829T002857 comment=NONE channel c3: backup set complete, elapsed time: 00:00:01 channel c2: finished piece 1 at 29-AUG-18 piece handle=/tmp/incr/datafile_18tbnqi9.bak tag=TAG20180829T002857 comment=NONE channel c2: backup set complete, elapsed time: 00:00:05 Finished backup at 29-AUG-18 released channel: c1 released channel: c2 released channel: c3 由于我这里这几个文件根本没有业务数据，所以效率提升尤为明显，只需要5s钟就完成了备份。 AlfredZhao©版权所有「从Oracle起航，领略精彩的IT技术。」https://www.cnblogs.com/jyzhao/p/9551866.html