15339 FIX check_sql: activate thick mode for oracle connections

With [Werk #16023](https://checkmk.com/werk/16023) we switched the
library used to connect to oracle databases from `cx_Oracle` to
`oracledb`. For `cx_Oracle` it was mandatory to install "Oracle Instant
Client". The newer `oracledb` library has two modes: A stand alone thin
mode and a thick mode that needs the "Oracle Instant Client".

In order to fully replace `cx_Oracle`, `oracledb` needs to be in thick
mode. This is something we have not considered for Werk #16023.

With this Werk we now try to switch into the thick mode, and if this
does not work, we use thin mode. If you execute `check_sql` with `-v`
switch you will see a message if `oracledb` could not switch into thick
mode.

`oracledb` searches for the "Oracle Instant Client" in several standard
location. `check_sql` will find the installation if the files (among
other things `*.so` and `*.jar`) from the "Oracle Instant Client" files
are directly in `~local/lib/` in your site.

SUP-19387

Change-Id: I0349197f239b2cc18c15ee8f11c05a61044bad04

.werks/15339.md

@@ -0,0 +1,30 @@
+[//]: # (werk v2)
+# check_sql: activate thick mode for oracle connections
+
+key        | value
+---------- | ---
+date       | 2024-08-08T09:40:54+00:00
+version    | 2.4.0b1
+class      | fix
+edition    | cre
+component  | checks
+level      | 1
+compatible | yes
+
+With [Werk #16023](https://checkmk.com/werk/16023) we switched the library used
+to connect to oracle databases from `cx_Oracle` to `oracledb`. For `cx_Oracle`
+it was mandatory to install "Oracle Instant Client". The newer `oracledb` library has
+two modes: A stand alone thin mode and a thick mode that needs the "Oracle
+Instant Client".
+
+In order to fully replace `cx_Oracle`, `oracledb` needs to be in thick mode.
+This is something we have not considered for Werk #16023.
+
+With this Werk we now try to switch into the thick mode, and if this does not
+work, we use thin mode. If you execute `check_sql` with `-v` switch you will see
+a message if `oracledb` could not switch into thick mode.
+
+`oracledb` searches for the "Oracle Instant Client" in several standard location.
+`check_sql` will find the installation if the files (among other things `*.so`
+and `*.jar`) from the "Oracle Instant Client" files are directly in
+`~local/lib/` in your site.

active_checks/check_sql

@@ -282,6 +282,19 @@ def oracle_connect(host: str, port: int, db_name: str, user: str, pwd: str) -> A
     except ImportError as exc:
         bail_out(3, "%s. Please install it via 'pip install oracledb'." % exc)
 
+    try:
+        oracledb.init_oracle_client()
+    except oracledb.DatabaseError as dbe:
+        # this seems to be the official way to differentiate between exceptions:
+        # https://python-oracledb.readthedocs.io/en/latest/user_guide/exception_handling.html#exception
+        if dbe.args[0].full_code == "DPI-1047":
+            LOG.info(
+                "Could not activate thick mode, will continue and use thin mode instead. "
+                "https://python-oracledb.readthedocs.io/en/latest/user_guide/initialization.html#initializing-python-oracledb"
+            )
+        else:
+            raise
+
     cstring = f"{user}/{pwd}@{host}:{port}/{db_name}"
     return oracledb.connect(cstring)