Oracle Database 18c XE is a free for use but with below limitations on H/W and memory:-
1. Instance:- We can only have one instance per server with the instance name XE. Please be aware that we cannot change the name of the instance. This is default and it is not clear whether we are allowed to change it.
2. Threads:- We can only have 2 user threads.
3. CPU:- We can only have 2 CPUs(max) in 18c XE. If your machine have more CPU’s it will not count more than two CPU’s.
4. Memory:- We can only have RAM up to 2GB(max).
5. Storage:- We can only have 12GB of user data stored (max).
Some important Key features in 18c XE :-
1. Pluggable databases :- Oracle Multitenant Container Database only can have Up to 3 Pluggable Databases.
2. Compression :- Basic Table Compression and Index Compression.
3. Encryption :- Transparent Data Encryption(TDE) which enables you to encrypt sensitive data that you store in tables and tablespaces.
4. partitioning :- Enhance performance, availability, and manageability.
We can now run multiple XE installations inside multiple VMs/Containers with one each. That means that we can run 4 instances on 4 VMs, one instance per VM.
ORA-04031 errors occurring in a RAC instance with the trace file showing high memory usage for "ges resource dynamic" and "ges enqueues" memory in the shared pool. This can cause LMD processes to become unresponsive leading to an instance termination.
The following query can be used to determine if this fix will help:
select substr(RESOURCE_NAME,instr(RESOURCE_NAME,'[',1,3)+1,2) , MASTER_NODE, count(*) from gv$ges_resource where substr(RESOURCE_NAME,instr(RESOURCE_NAME,'[',1,3)+1,2) in ('DX', 'BB') group by substr(RESOURCE_NAME,instr(RESOURCE_NAME,'[',1,3)+1,2), MASTER_NODE order by 3 desc;
If that shows a large number of entries (much larger than the expected total number of transactions), then this fix will help.
CAUSE for ORA-04031
This is due to unpublished bug:21373473 fixed in 12.2, and occurs due to DX and BB locks being cached but not cleared out. This fix removes the need to cache DX and BB locks and hence reduces overall shared pool memory usage in RAC instances. ORA-04031 errors occurring with high memory utilization for "ges enqueues" & "ges resource dynamic" memory allocations.
SOLUTION Download and apply the one-off patch number 21373473 (Patch:21373473) for your platform and version combination. Please note that if using 126.96.36.199, then you should also apply the related patch number 21260431 (Patch:21260431) which also impacts the shared pool memory allocations identified here.
This issue can also be worked around by setting _GES_DIRECT_FREE_RES_TYPE="CTARAHDXBB" in the instances.
Note:- We also found ORA-01041: internal error. hostdef extension doesn't exist in alert logs that depends on ORA-04031. also suggest to open a Service request with oracle if not sure with above method.
ORA-02051 Another Session Or Branch In Same Transaction Failed (Doc ID 2253226.1)
SYMPTOMS for ORA-02051 Another Session Or Branch In Same Transaction Failed. Database performance is slow and caused the transactions ORA-02051 another session or branch in same transaction failed or finalized
CAUSE for ORA-02051 Another Session Or Branch In Same Transaction Failed. Session transactions branches caused the issue Excessive Waits On The Event "Global transaction acquire instance locks"
SOLUTION Please use below sql and identified underscore parameter values for ORA-02051 Another Session Or Branch In Same Transaction Failed : SQL> select a.ksppinm "Parameter", b.ksppstvl "Session Value",c.ksppstvl "Instance Value" FROM x$ksppi a,x$ksppcv b, x$ksppsv c WHERE a.indx = b.indx AND a.indx = c.indx AND a.ksppinm LIKE '/_%' escape '/' AND (a.ksppinm like '%clusterwide_global%' or a.ksppinm like '%disable_autotune_gtx%') ;
Parameter Session Value Instance Value ---------------------------------------- -------------------- -------------------- _clusterwide_global_transactions TRUE TRUE _disable_autotune_gtx FALSE FALSE
Set following to solver ORA-02051 Another Session Or Branch In Same Transaction Failed :- alter system set "_clusterwide_global_transactions"=false scope=spfile; alter system set "_disable_autotune_gtx"=TRUE scope = spfile; Note:- bounce the instances for the changes to take effect