datapatch throws Error: prereq checks failed! patch 32218454: Error reading descriptor from registry: Couldn't open encmap cp866.enc: No such file or directory

I caught this error when I was running $ORACLE_HOME/OPatch/datapatch -verbose command to apply all the patches of 19.14 RU to 19.13 CDB and its PDBs. The error looked like this :

$ $ORACLE_HOME/OPatch/datapatch -verbose
SQL Patching tool version 19.14.0.0.0 Production on Wed Sep 14 20:31:36 2022
Copyright (c) 2012, 2021, Oracle.  All rights reserved.

Log file for this invocation: /u01/app/oracle/cfgtoollogs/sqlpatch/sqlpatch_29306_2022_09_14_20_31_36/sqlpatch_invocation.log

Connecting to database...OK
Gathering database info...done

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...done
Determining current state...done

...

 PDB PDB2:
   Applied 19.13.0.0.0 Release_Update 211010063823 successfully on 16-NOV-21 07.25.29.732858 PM

Error: prereq checks failed!
 patch 32218454: Error reading descriptor from registry: Couldn't open encmap cp866.enc:
No such file or directory
at /u01/app/oracle/product/19/db_1914/perl/lib/site_perl/5.28.1/sun4-solaris-thread-multi-64/XML/Parser.pm line 187.
XML::Simple called at /u01/app/oracle/product/19/db_1914/sqlpatch/sqlpatch.pm line 8123.

Prereq check failed, exiting without installing any patches.

Please refer to MOS Note 1609718.1 and/or the invocation log
/u01/app/oracle/cfgtoollogs/sqlpatch/sqlpatch_29306_2022_09_14_20_31_36/sqlpatch_invocation.log
for information on how to resolve the above errors.

SQL Patching tool complete on Wed Sep 14 20:32:23 2022

I can only guess why this error happened. Recently I plugged PDB with codepage RU8PC866 over the network and deleted it after a while. So some information had left inside registry$sqlpatch, and I can assume, it has xml part presented in ru8pc866 codepage. The datapatch invokes perl. The information is parsed by xml-parser perl module (from ORACLE_HOME). It seemed that possible solution was rebuilding registry$sqlpatch (required downtime, sounacceptable) or trying to find missed file (I chose the second). 

So, perl module xml-parser has got the following supported (from the box) codepages :

$ l $ORACLE_HOME/perl/lib/site_perl/5.28.1/sun4-solaris-thread-multi-64/XML/Parser/Encodings/
total 554
drwxr-xr-x   2 oracle   oinstall      26 Sep 14 23:01 .
drwxr-xr-x   4 oracle   oinstall       6 Mar 10  2022 ..
-rwxr-x---   1 oracle   oinstall   40706 Mar 26  2019 big5.enc
-rwxr-x---   1 oracle   oinstall   45802 Mar 26  2019 euc-kr.enc
-rwxr-x---   1 oracle   oinstall    1072 Mar 26  2019 ibm866.enc
-rwxr-x---   1 oracle   oinstall    1072 Mar 26  2019 iso-8859-2.enc
-rwxr-x---   1 oracle   oinstall    1072 Mar 26  2019 iso-8859-3.enc
-rwxr-x---   1 oracle   oinstall    1072 Mar 26  2019 iso-8859-4.enc
-rwxr-x---   1 oracle   oinstall    1072 Mar 26  2019 iso-8859-5.enc
-rwxr-x---   1 oracle   oinstall    1072 Mar 26  2019 iso-8859-7.enc
-rwxr-x---   1 oracle   oinstall    1072 Mar 26  2019 iso-8859-8.enc
-rwxr-x---   1 oracle   oinstall    1072 Mar 26  2019 iso-8859-9.enc
-rwxr-x---   1 oracle   oinstall    4821 Mar 26  2019 Japanese_Encodings.msg
-rwxr-x---   1 oracle   oinstall    1072 Mar 26  2019 koi8-r.enc
-rwxr-x---   1 oracle   oinstall    1950 Mar 26  2019 README
-rwxr-x---   1 oracle   oinstall    1072 Mar 26  2019 windows-1250.enc
-rwxr-x---   1 oracle   oinstall    1072 Mar 26  2019 windows-1251.enc
-rwxr-x---   1 oracle   oinstall    1072 Mar 26  2019 windows-1252.enc
-rwxr-x---   1 oracle   oinstall    1072 Mar 26  2019 windows-1255.enc
-rwxr-x---   1 oracle   oinstall   37890 Mar 26  2019 x-euc-jp-jisx0221.enc
-rwxr-x---   1 oracle   oinstall   37890 Mar 26  2019 x-euc-jp-unicode.enc
-rwxr-x---   1 oracle   oinstall   20368 Mar 26  2019 x-sjis-cp932.enc
-rwxr-x---   1 oracle   oinstall   18202 Mar 26  2019 x-sjis-jdk117.enc
-rwxr-x---   1 oracle   oinstall   18202 Mar 26  2019 x-sjis-jisx0221.enc
-rwxr-x---   1 oracle   oinstall   18202 Mar 26  2019 x-sjis-unicode.enc

I needed to find cp866.enc file somewhere. The README file says :

This directory contains binary encoding maps for some selected encodings.
If they are placed in a directory listed in @XML::Parser::Expat::Encoding_Path,
then they are automatically loaded by the XML::Parser::Expat::load_encoding
function as needed. Otherwise you may load what you need directly by
explicitly calling this function.

These maps were generated by a perl script that comes with the module
XML::Encoding, compile_encoding, from XML formatted encoding maps that
are distributed with that module. These XML encoding maps were generated
in turn with a different script, domap, from mapping information contained
on the Unicode version 2.0 CD-ROM. This CD-ROM comes with the Unicode
Standard reference manual and can be ordered from the Unicode Consortium
at http://www.unicode.org. The identical information is available on the
internet at ftp://ftp.unicode.org/Public/MAPPINGS.

So the task is to find both the scripts and get the source of 866 codepage (found CP866.TXT on ftp://ftp.unicode.org/Public/MAPPINGS/VENDORS/MICSFT/PC)

Both compile_encoding and domap (actually, make_encmap) scripts I found in libxml-encoding-perl_2.09-1_all.deb (untar data.tar.xz from downloaded file). So, do these steps :

tar xf ./data.tar.xz 

cd usr/bin

./make_encmap cp866 /temp/service_request/perl/CP866.TXT > cp866_make.out

Edit cp866_make.out (it's actually an xml description of codepage 866) to add expat='yes' at the first line and compile :

<encmap name='cp866' expat='yes'>

./compile_encoding -o cp866.enc cp866_make.out

Put the cp866.enc file into perl module's xml-parser encodings directory, for me it was /u01/app/oracle/product/19/db_1914/perl/lib/site_perl/5.28.1/sun4-solaris-thread-multi-64/XML/Parser/Encodings

and rerun datapatch. In my particular case I cought another error not related to this topic :

Unsupported named object type for bind parameter at /u01/app/oracle/product/19/db_1914/sqlpatch/sqlpatch.pm line 5783.

The cause of it was an absense of tempfile inside one of PDB's temporary tablespace. After adding I ended up with whole CDB patched.

The conclusion : do not use stale and deprecated codepages to keep your data in 😀 ! Oracle recommends all its customers to migrate to AL32UTF8 (but it requres much efforst in many cases and it depends, actually...)

PS. I still don't understand how the patch numbered 32218454 (database 19.10 RU) has turned out to be a cause of this issue. Only one assumption : it had been used with one of PDBs ORACLE_HOME before being plugged in into CDB.

When crontab schedule is not enough

As far as you know, cron provides the schedule on the following time attributes: minute, hour, day of the week, month, day of month. What if you need to set the specific schedule, for example, you need (not) to fire the event only on last working day of the current month and on the next day after it (2 days in a row) ? 

The application is restarting every day. Let's assume that working days between Monday and Friday, the current month (September) has 30 days, and last working day is Friday, 28th. So, we need (not) to fire the event on 28th and 29th. How to do this using only crontab file ? Have a look :

#
# If END_OF_MONTH=true, the app server is not stopped and not restarted automatically.
# END_OF_MONTH is set to true when current day is last working day of month, and next day after it (2 days in row).
# a and b - intermediate variables to keep END_OF_MONTH intermediate value.
# Exception when 30.04 is Monday (as in 2018 and 2029; then end of month must be moved to Saturday, 28.04, because 01.05 (day off) is Tuesday),
# or 29.04 is Radonica (in 2025 and 2036, so 30.04 is moved to 03.05, end of month in this case 28.04).
#
cy='date +%Y'
cm='LANG=en date +%b'
nm1wd='$(test $(eval $cm) = "Dec") && eval $(echo "LANG=en date +%u -d \"$(LANG=en date +%b -d "next month") 1 +1year\"") || eval $(echo "LANG=en date +%u -d \"$(LANG=en date +%b -d "next m
onth") 1\"")'
lcmd='LANG=en date +%d -d "$(LANG=en date +%b -d "next month") 1 -1day"'
cday='date +%-d'
cwday='date +%u'
fr1="cal -m | tail -n +3 | awk '{print $5}' | sed -n '4p'"
fr2="cal -m | tail -n +3 | awk '{print $5}' | sed -n '5p'"
last_fr='test -z "$(eval $fr2)" && echo $(eval $fr1) || echo $(eval $fr2)'
sa1="cal -m | tail -n +3 | awk '{print $6}' | sed -n '4p'"
sa2="cal -m | tail -n +3 | awk '{print $6}' | sed -n '5p'"
last_sa='test -z "$(eval $sa2)" && echo $(eval $sa1) || echo $(eval $sa2)'
_END_OF_MONTH='$(test $(eval $nm1wd) -ge 3 -a $(eval $nm1wd) -le 5 -a $(eval $cday) -eq $(eval $lcmd) || (test $(eval $nm1wd) -eq 6 -a $(eval $cday) -eq $(eval $last_fr)) || (test $(eval $n
m1wd) -eq 7 -o $(eval $nm1wd) -eq 1 && test $(eval $cday) -eq $(eval $last_fr) -o $(eval $cday) -eq $(eval $last_sa)) || test $(eval $nm1wd) -eq 2 -a $(eval $cday) -eq $(eval $last_sa) || t
est $(eval $cday) -eq 1 -a $(eval $cwday) -ge 2 -a $(eval $cwday) -le 6) && echo true'
apr_d='LANG=en date +%d%b%a'
apr_eom='$(test $(eval $apr_d) = "28AprSat" -o $(eval $apr_d) = "29AprSun" -o $(eval $apr_d) = "28AprMon" -o $(eval $apr_d) = "29AprTue") && echo true || echo false'
apr_no_eom='$(test $(eval $apr_d) = "30AprMon" -o $(eval $apr_d) = "01MayTue" -o $(eval $apr_d) = "30AprWed" -o $(eval $apr_d) = "01MayThu") && echo true || echo false'
END_OF_MONTH='$(test $(eval $apr_eom) = "true" -a $(eval $cy) != "2031" ) && echo true || echo $(eval $_END_OF_MONTH)'
END_OF_MONTH='$(test $(eval $apr_no_eom) = "true" -a $(eval $cy) != "2031" ) && echo false || echo $(eval $_END_OF_MONTH)'
END_OF_MONTH='$(test \( $(eval $apr_d) = "27AprSat" -o $(eval $apr_d) = "28AprSun" \) -a $(eval $cy) = "2041") && echo true || echo $(eval $_END_OF_MONTH)'
END_OF_MONTH='$(test \( $(eval $apr_d) = "30AprTue" -o $(eval $apr_d) = "01MayWed" \) -a $(eval $cy) = "2041") && echo false || echo $(eval $_END_OF_MONTH)'
 

00    02    *   *     *           [ "$(echo $(eval $END_OF_MONTH))" != "true" ] && su - app_user -c "/home/app_user/app stop"

00    03    *   *     1-7         [ "$(echo $(eval $END_OF_MONTH))" != "true" ] && su - app_user -c "/home/app_user/app restart"

The logic is build around using bash eval and test buildin commands. If END_OF_MONTH is set to true, then nothing happens, app stop and restart tasks aren't run. There are couple of exceptions regarding to my country : 1st of May and Cristian Orthodox holiday named Radonica are always day off; because of this the movements of day off and working days are possible. I tried to count these exceptions in crontab too.

Good Luck !