What is the "datapatch" utility released in Oracle 12c?

From Datapatch: Database 12c Post Patch SQL Automation (Doc ID 1585822.1):

Datapatch is the new tool that enables automation of post-patch SQL actions for RDBMS patches.

and

Datapatch can be executed to complete post-patch SQL actions after the database is restarted following patch application.
For patches that do not have post-patch SQL actions to be performed, calling datapatch is a no-op.
For patches that do have post-patch SQL instructions to be invoked on the database instance, datapatch will automatically detect ALL pending actions (from one installed patch or multiple installed patches) and complete the actions as appropriate.

How does Oracle detect ALL pending actions?

Datapatch determines the requisite apply/rollback actions by matching an internal repository with the patch inventory.


When should datatach be invoked?

Datapatch should be invoked when the database is restarted after a patching session.

From 12.1.0.2 and onwards, Oracle Corporation points out that they have made some change to the datapatch utility. The most important in my opinion is that datapatch now assumes "the role of catbundle when applying bundles/PSU."

This means that

catbundle.sql has been deprecated and patch registry is maintained only in registry$sqlpatch.
Application of the PSU does not update registry$history table anymore.
The status for patch application is now entirely maintained in registry$sqlpatch


Here's an abbreviated output from using datapatch as part of applying Oracles latest PSU, Database Patch Set Update 12.1.0.2.170814 (Includes CPUJul2017):

1. Download and unpack the patch

[oracle@lx01oric software]$ unzip p26609783_121020_Linux-x86-64.zip

2. Shutdown your oracle instance and the listener
3. Check for conflicts:

[oracle@lx01oric software]$ cd 26609783
oracle@lx01oric 26609783]$ opatch prereq CheckConflictAgainstOHWithDetail -ph ./
Oracle Interim Patch Installer version 12.1.0.1.3
Copyright (c) 2017, Oracle Corporation.  All rights reserved.

PREREQ session

Oracle Home       : /u01/oracle/product/db/12.1/12.1.0.2.0
Central Inventory : /u01/oraInventory
   from           : /u01/oracle/product/db/12.1/12.1.0.2.0/oraInst.loc
OPatch version    : 12.1.0.1.3
OUI version       : 12.1.0.2.0
Log file location : /u01/oracle/product/db/12.1/12.1.0.2.0/cfgtoollogs/opatch/opatch2017-09-06_13-41-14PM_1.log

Invoking prereq "checkconflictagainstohwithdetail"

Prereq "checkConflictAgainstOHWithDetail" passed.

OPatch succeeded.

4. Apply the patch:

[oracle@lx01oric 26609783]$ opatch apply
Oracle Interim Patch Installer version 12.2.0.1.9
Copyright (c) 2017, Oracle Corporation.  All rights reserved.


Oracle Home       : /u01/oracle/product/db/12.1/12.1.0.2.0
Central Inventory : /u01/oraInventory
   from           : /u01/oracle/product/db/12.1/12.1.0.2.0/oraInst.loc
OPatch version    : 12.2.0.1.9
OUI version       : 12.1.0.2.0
Log file location : /u01/oracle/product/db/12.1/12.1.0.2.0/cfgtoollogs/opatch/opatch2017-09-06_14-16-35PM_1.log

Verifying environment and performing prerequisite checks...
OPatch continues with these patches:   19769480  20299023  20831110  21359755  21948354  22291127  23054246  24006101  24732082  25171037  25755742  26609783  

Do you want to proceed? [y|n]

... output abbreviated.

Composite patch 26609783 successfully applied.
Log file location: /u01/oracle/product/db/12.1/12.1.0.2.0/cfgtoollogs/opatch/opatch2017-09-06_14-16-35PM_1.log

OPatch succeeded.

5. Start your database. When opened, execute datapatch:

[oracle@lx01oric] cd $ORACLE_HOME/OPatch
[oracle@lx01oric OPatch]$ ./datapatch -verbose
SQL Patching tool version 12.1.0.2.0 Production on Wed Sep  6 14:54:49 2017
Copyright (c) 2012, 2016, Oracle.  All rights reserved.

Log file for this invocation: /u01/oracle/cfgtoollogs/sqlpatch/sqlpatch_16001_2017_09_06_14_54_50/sqlpatch_invocation.log

Connecting to database...OK
Note:  Datapatch will only apply or rollback SQL fixes for PDBs
       that are in an open state, no patches will be applied to closed PDBs.
       Please refer to Note: Datapatch: Database 12c Post Patch SQL Automation
       (Doc ID 1585822.1)
Bootstrapping registry and package to current versions...
Bootstrap timed out after 240 seconds
Retrying bootstrap after retryable errors....done
Determining current state...done

Current state of SQL patches:
Bundle series PSU:
  ID 170814 in the binary registry and not installed in any PDB

Adding patches to installation queue and performing prereq checks...
Installation queue:
  For the following PDBs: CDB$ROOT PDB$SEED
    Nothing to roll back
    The following patches will be applied:
      26609783 (DATABASE PATCH SET UPDATE 12.1.0.2.170814)

Installing patches...
Patch installation complete.  Total patches installed: 2

Validating logfiles...
Patch 26609783 apply (pdb CDB$ROOT): SUCCESS
  logfile: /u01/oracle/cfgtoollogs/sqlpatch/26609783/21481899/26609783_apply_CDBVEG_CDBROOT_2017Sep06_15_01_26.log (no errors)
Patch 26609783 apply (pdb PDB$SEED): SUCCESS
  logfile: /u01/oracle/cfgtoollogs/sqlpatch/26609783/21481899/26609783_apply_CDBVEG_PDBSEED_2017Sep06_15_09_34.log (no errors)
SQL Patching tool complete on Wed Sep  6 15:18:53 2017
[oracle@lx01oric OPatch]$ vi /u01/oracle/cfgtoollogs/sqlpatch/26609783/21481899/26609783_apply_CDBVEG_PDBSEED_2017Sep06_15_09_34.log

6. If applicable, activate the OJVM Mitigation patch.

According to Oracle, this patch is applicable in "situations where the latest OJVM PSU cannot be installed immediately... The "Mitigation Patch" is an interim solution to protect against all currently known (Jul 2015) Oracle JavaVM security vulnerabilities in the database until such time as the OJVM PSU can be installed."

Since this is my situation, I install the mitigation patch:

[oracle@lx01oric 26609783]$ cd $ORACLE_HOME/rdbms/admin
[oracle@lx01oric admin]$ sqlplus / as sysdba @dbmsjdev.sql
[oracle@lx01oric admin]$ sqlplus / as sysdba
SQL> exec dbms_java_dev.disable;
PL/SQL procedure successfully completed.
SQL>