I have installed Oracle 19.6 on an EC2 for our Multitenant Workshop training. And of course, during the workshop we create a lot of PDBs. If you don’t have paid for the Enterprise Edition plus the Multitenant Option you can create at most 3 pluggable database. But with this option you can create up to 252 pluggable databases. Does it worth the price, which according to the public price list is USD 47,500 + 17,500 per processor, which means per-core because Oracle doesn’t count the core factor when your Intel processors are in AWS Cloud (according to the Authorized Cloud Environments paper)? Probably not because Oracle detects where you run and bridles some features depending whether you are on the Dark or the Light Side of the public cloud (according to their criteria of course).

At one point I have 3 pluggable databases in my CDB:

SQL> show pdbs
_________ ____________ ____________ _____________
        2 PDB$SEED     READ ONLY    NO
        3 CDB1PDB01    MOUNTED
        4 CDB1PDB03    MOUNTED
        5 CDB1PDB02    MOUNTED

I want to create a 4th one:

SQL> create pluggable database CDB1PDB04 from CDB1PDB03;

create pluggable database CDB1PDB04 from CDB1PDB03
ERROR at line 1:
ORA-65010: maximum number of pluggable databases created

It fails. The maximum number of pluggable databases is defined by MAX_PDBS, but I defined nothing in my SPFILE:

SQL> show spparameter max_pdbs
--- -------- ------- -----
*   max_pdbs integer

I thought that the default was 4098 (which is incorrect anyway as you cannot create more than 4096) but it is actually 5 here:

SQL> show parameter max_pdbs
-------- ------- -----
max_pdbs integer 5

Ok… this parameter is supposed to count the number of user pluggable databases (the ones with CON_ID>2) and I have 3 of them here. The limit is 5 and I have an error mentioning that I’ve reached the limit. That’s not the first time I see wrong maths with this parameter. But there’s worse as I cannot change it:

SQL> alter system set max_pdbs=6;

alter system set max_pdbs=6
ERROR at line 1:
ORA-02097: parameter cannot be modified because specified value is invalid
ORA-65334: invalid number of PDBs specified

I can change it in the SPFILE but it doesn’t help me to create more pluggable databases:

SQL> alter system set max_pdbs=200 scope=spfile;

System altered.

SQL> startup force;

Total System Global Area   2147482744 bytes
Fixed Size                    9137272 bytes
Variable Size               587202560 bytes
Database Buffers           1543503872 bytes
Redo Buffers                  7639040 bytes
Database mounted.
Database opened.

SQL> show parameter max_pdbs
-------- ------- -----
max_pdbs integer 200

SQL> create pluggable database CDB1PDB04 from CDB1PDB03;

create pluggable database CDB1PDB04 from CDB1PDB03
ERROR at line 1:
ORA-65010: maximum number of pluggable databases created

Something bridles me. There’s a MOS Note ORA-65010 When Oracle Database Hosted on AWS Cloud (Doc ID 2328600.1) about the same problem but that’s in (before MAX_PDBS was introduced) which is supposed to be fixed in AUG 2017 PSU. But here I am 3 years later in 19.6 (the January 2020 Release Update for the latest version available on-premises).

So, Oracle limits the number of pluggable databases when we are on a public cloud provider which is not the Oracle Public Cloud. This limitation is not documented in the licensing documentation which mentions 252 as the Enterprise Edition limit, and I see nothing about “Authorized Cloud Environments” limitations for this item. This, and the fact that it can come and go with Release Updates put customers at risk when running on AWS EC2: financial risk and availability risk. I think there are only two choices, on long term, when you want to run your database on a cloud: go to Oracle Cloud or leave for another Database.

How does the Oracle instance know on which public cloud you run? All cloud platforms provide some metadata through HTTP api. I have straced all sendto() and recvfrom() system calls when starting the instance:

strace -k -e trace=recvfrom,sendto -yy -s 1000 -f -o trace.trc sqlplus / as sysdba <<<'startup force'

And I searched for Amazon and AWS here:

This is clear: the instance has a function to detect the cloud provider (kgcs_clouddb_provider_detect) when initializing the SGA in a multitenant architecture (kpdbInitSga) with the purpose of detecting non-oracle clouds (kscs_is_non_oracle_cloud). This queries the AWS metadata (documented on Retrieving Instance Metadata):

[oracle@ora-cdb-1 ~]$ curl

When Oracle software sees the name of the enemy in the domain name amazonaws.com, it sets an internal limit for the number of pluggable databases that overrides the MAX_PDBS setting. Ok, I don’t need this metadata and I’m root on EC2 so my simple workaround is to block this metadata API:

[root@ora-cdb-1 ~]# iptables -A OUTPUT -d  -j REJECT
[root@ora-cdb-1 ~]# iptables -L
Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination
REJECT     udp  --  anywhere                udp dpt:domain reject-with icmp-port-unreachable
REJECT     all  --  anywhere                reject-with icmp-port-unreachable

Then restart the instance and it works: I can set or reset MAX_PDBS and create more pluggable databases.

I can remove the rule

[root@ora-cdb-1 ~]# iptables -D OUTPUT -d  -j REJECT

If, for watever reason I want to revert back.

Finally, because they had many bugs with the MAX_PDBS soft limit, there’s a parameter to disable it and this disables also the hard limit:

SQL> alter system set "_cdb_disable_pdb_limit"=true scope=spfile;
System altered.

Thanks to Mauricio Melnik for the heads-up on that:

However, with this parameter you cannot control anymore the maximum number of PDBs so don’t forget to monitor your AUX_COUNT in DBA_FEATURE_USAGE_STATISTICS.

Here was my discovery when preparing the multitenant workshop lab environment. Note that given the current situation where everybody works from home when possible, we are ready to give this training full of hands-on exercises though Microsoft Teams and AWS EC2 virtual machines. Two days to be comfortable when moving to CDB architecture, which is what should be done this year when you plan to stay with Oracle Database for the future versions.

Update 27-MAR-2020

In order not to sound too negative here, this limit on AWS platforms has been removed in the past and this may be a bug re-introduced with the change from 1 to 3 PDBs in Standard Edition.