.
\nWhen non-CDB has been declared deprecated, I was a bit upset because multitenant with a lone PDB just looks like an overhead of 3 containers instead of one. But with experience I changed my mind. First because the multitenant architecture brings some features that are available even without the option. And second, because this overhead is not a big problem. Let’s put numbers on that last point.
\n
\nA CDB has 3 containers: CDB$ROOT, PDB$SEED, and your pluggable database. Each one has SYSTEM and SYSAUX tablespaces. Even if the pluggable database system tablespaces are smaller thanks to metadata links, it’s still more datafiles and more space. There are also more processes.<\/p>\n
I’ve created a non-CDB and a CDB with same configuration and same virtual machines. Oracle Cloud Services is very nice for that.<\/p>\n
Here is the storage after the database creation.
\nFirst on the Multitenant one:<\/p>\n
\n[oracle@vicdb ~]$ df -h\nFilesystem Size Used Avail Use% Mounted on\n\/dev\/xvdb3 25G 17G 7.7G 68% \/\ntmpfs 7.3G 0 7.3G 0% \/dev\/shm\n\/dev\/xvdb1 477M 148M 300M 34% \/boot\n[oracle@vicdb ~]$\n \n[oracle@vinon ~]$ du -xh \/u01\/app\/oracle\/oradata | sort -h\n9.6M \/u01\/app\/oracle\/oradata\/NON\/controlfile\n151M \/u01\/app\/oracle\/oradata\/NON\/onlinelog\n1.6G \/u01\/app\/oracle\/oradata\/NON\/datafile\n1.8G \/u01\/app\/oracle\/oradata\n1.8G \/u01\/app\/oracle\/oradata\/NON\n<\/code><\/pre>\nAnd in the non-CDB one:<\/p>\n
\n[oracle@vinon ~]$ df -h\nFilesystem Size Used Avail Use% Mounted on\n\/dev\/xvdb3 25G 15G 9.1G 62% \/\ntmpfs 7.3G 0 7.3G 0% \/dev\/shm\n\/dev\/xvdb1 477M 148M 300M 34% \/boot\n \n[oracle@vicdb ~]$ du -xh \/u01\/app\/oracle\/oradata | sort -h\n18M \/u01\/app\/oracle\/oradata\/CDB\/controlfile\n151M \/u01\/app\/oracle\/oradata\/CDB\/onlinelog\n741M \/u01\/app\/oracle\/oradata\/CDB\/2F81FDFC05495272E053CE46C40ABDCF\n741M \/u01\/app\/oracle\/oradata\/CDB\/2F81FDFC05495272E053CE46C40ABDCF\/datafile\n2.4G \/u01\/app\/oracle\/oradata\/CDB\/datafile\n3.3G \/u01\/app\/oracle\/oradata\n3.3G \/u01\/app\/oracle\/oradata\/CDB\n<\/code><\/pre>\nThe CDB system needs additional 1.4GB for the additional tablespaces.
\nIf you think about it, the overhead is minimal when you compare it with the size of your database.<\/p>\n
That’s for storage. Let’s have a look at memory.<\/p>\n
Here is the Multitenant system<\/p>\n
\ntop - 10:20:00 up 2:26, 2 users, load average: 0.00, 0.04, 0.13\nTasks: 164 total, 1 running, 163 sleeping, 0 stopped, 0 zombie\nCpu(s): 0.1%us, 0.0%sy, 0.0%ni, 99.8%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st\nMem: 15138468k total, 14783080k used, 355388k free, 125580k buffers\nSwap: 4194300k total, 0k used, 4194300k free, 13845468k cached\n \n PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND\n20854 oracle -2 0 4790m 19m 17m S 2.4 0.1 0:19.75 ora_vktm_cdb\n20890 oracle 20 0 4810m 129m 112m S 0.1 0.9 0:01.70 ora_mmon_cdb\n20870 oracle 20 0 4793m 25m 21m S 0.1 0.2 0:00.71 ora_dia0_cdb\n20892 oracle 20 0 4791m 40m 38m S 0.1 0.3 0:00.69 ora_mmnl_cdb\n21306 oracle 20 0 4791m 26m 24m S 0.0 0.2 0:00.03 ora_j000_cdb\n20852 oracle 20 0 4790m 19m 17m S 0.0 0.1 0:00.20 ora_psp0_cdb\n20876 oracle 20 0 4791m 51m 48m S 0.0 0.3 0:00.23 ora_ckpt_cdb\n20957 oracle 20 0 4801m 69m 57m S 0.0 0.5 0:00.49 ora_cjq0_cdb\n 12 root RT 0 0 0 0 S 0.0 0.0 0:00.05 watchdog\/1\n20866 oracle 20 0 4793m 44m 40m S 0.0 0.3 0:00.27 ora_dbrm_cdb\n20872 oracle 20 0 4800m 76m 67m S 0.0 0.5 0:00.21 ora_dbw0_cdb\n20911 oracle 20 0 4790m 19m 17m S 0.0 0.1 0:00.04 ora_tt00_cdb\n<\/code><\/pre>\nand the CDB one:<\/p>\n
\ntop - 10:21:04 up 2:10, 2 users, load average: 0.00, 0.01, 0.10\nTasks: 154 total, 1 running, 153 sleeping, 0 stopped, 0 zombie\nCpu(s): 1.8%us, 0.6%sy, 0.2%ni, 96.5%id, 0.6%wa, 0.0%hi, 0.0%si, 0.3%st\nMem: 15138468k total, 12102812k used, 3035656k free, 167644k buffers\nSwap: 4194300k total, 0k used, 4194300k free, 11260644k cached\n \n PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND\n21539 oracle -2 0 4790m 19m 17m S 2.0 0.1 0:32.69 ora_vktm_non\n22095 oracle 20 0 15088 1164 856 R 2.0 0.0 0:00.01 top\n 1 root 20 0 19408 1540 1232 S 0.0 0.0 0:00.69 init\n 2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd\n 3 root 20 0 0 0 0 S 0.0 0.0 0:00.05 ksoftirqd\/0\n 5 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 kworker\/0:0H\n 6 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kworker\/u:0\n 7 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 kworker\/u:0H\n 8 root RT 0 0 0 0 S 0.0 0.0 0:00.25 migration\/0\n 9 root 20 0 0 0 0 S 0.0 0.0 0:00.00 rcu_bh\n 10 root 20 0 0 0 0 S 0.0 0.0 0:01.02 rcu_sched\n<\/code><\/pre>\nWith same SGA sizing the memory footprint is the similar. And you don’t need to setup a larger SGA for single-tenant: buffer cache is the same (depends on your data), library cache is the same (depends on your code), dictionary cache may be a bit larger but it’s still small. Basically it run exactly the same except that objects have a container id (which is only one byte in 12.1).<\/p>\n
I think it’s enough to clear out the myth that single-tenant has a big overhead over non-CDB. <\/p>\n
For sure, it’s a bit strange to have to store a PDB$SEED, which is used only to create new pluggable databases, when we cannot create additional pluggable databases. In single-tenant, you will probably have one CDB with your own seed in read-only, and you can remote clone from it. And it’s right that multitenant architecture has been implemented for the multitenant option. But there is no reason to refuse it. With minimal overhead, you can benefit from lot of features that are possible with the dictionary separation. Let’s take a single example: in Standard Edition you can move a whole database physically by unplug\/plug or remote clone. When you realize that transportable tablespaces have never been available in Standard Edition can see unplug\/plug as a great enhancement for Standard Edition. Easier than duplicate, and cross-version, cross-platform. Perfect for migrations.<\/p>\n","protected":false},"excerpt":{"rendered":"
By Franck Pachot . When non-CDB has been declared deprecated, I was a bit upset because multitenant with a lone PDB just looks like an overhead of 3 containers instead of one. But with experience I changed my mind. First because the multitenant architecture brings some features that are available even without the option. And […]<\/p>\n","protected":false},"author":27,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[229],"tags":[220,64,96,209,66,223],"type_dbi":[],"class_list":["post-7525","post","type-post","status-publish","format-standard","hentry","category-database-administration-monitoring","tag-cdb","tag-multitenant","tag-oracle","tag-oracle-12c","tag-pdb","tag-pluggable-databases"],"acf":[],"yoast_head":"\n
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