Fix documentation for UDF debugging

[ckunki]

See also https://github.com/exasol/impala-virtual-schema/issues/13 and https://github.com/exasol/hive-virtual-schema/issues/31

Logging mechanisms

• Logging mechanism (L1): UDF Framework via tcp
  • Script output redirect
  • Can be used for arbitrary programming languages
  • Enables to analyse problems on lower levels
  • Example: problems caused by JVM parameters
  • Redirects stdout / stderr of containers to external server
• Logging mechanism (L2) "Virtual Schema logging" via tcp
  • Can only be used for Java and a virtual machine
  • Redirects Java logging to external server

Documentation on docs.exasol.com

Currently docs.exasol.com describes three different approaches for UDF logging.

• Debug UDF Script Output mentions a different script udf_debug.py with identical name
  • repository hadoop-etl-udfs is archived, though.
  • referred script is available only for Python 2.0 and has not been ported to Python 3, yet.
• "For Python 3.x" mentions pyexasol debug mode which is
  • preferred
  • but currently limited to a single connection
• Virtual Schema Logging describes nc -lkp which requires neither python nor pyexasol but also some limitations
  • not available on windows or requires installation of additional software
  • output of potentially multiple clients is merged and cannot be separated

[allipatev]

Microsoft Windows [Version 10.0.22000.1219]
(c) Microsoft Corporation. All rights reserved.

C:\Users\<my user name>>nc
'nc' is not recognized as an internal or external command,
operable program or batch file.

[ckunki]

On windows one could potentially use https://nmap.org/ncat/

[ckunki]

https://github.com/exasol/exasol-python-test-framework/blob/master/exasol_python_test_framework/udf/udf_debug.py

[ckunki]

See https://github.com/exasol/exasol-python-test-framework/issues/42 for follow up