I am getting below error messages while gathering stats (BEGIN DBMS_STATS.GATHER_SCHEMA_STATS):
ORA-12801: error signaled in parallel query server P030, instance <Servernode>
ORA-00600: internal error code, arguments: [qeshQBNextBuffer.1], , , , , , , , , , , 
ORA-06512: at "SYS.DBMS_STATS", line 24098
ORA-06512: at "SYS.DBMS_STATS", line 24176
ORA-06512: at "SYS.DBMS_STATS", line 24130
ORA-06512: at line 1
Degree used is 4.
this problem occured from "HASH GROUP BY" so you can modify sql statement used hint as bellow
SELECT /*+ no_use_hash_aggregation */ FROM WHERE GROUP BY ?
alter session set "_gby_hash_aggregation_enabled"=false ;
pls take a look this doc
ORA-00600 [QESHQBNEXTBUFFER.1] While Inserting into Table [ID 421341.1]
This is the generic internal error number for Oracle program exceptions. It indicates that a process has encountered a low-level, unexpected condition.
Suggestion use My Oracle Support. http://support.oracle.com
1 - use note: ORA-600/ORA-7445/ORA-700 Error Look-up Tool [ID 153788.1], to check bug.
If you don't find anything about:
2 - Report this error to Oracle Support Services opening a SR.