doc: logging improvement and readme

README.md

@@ -196,8 +196,10 @@ How often the scheduler checks the database for due executions. Default `10s`.<b
 The Scheduler assumes that columns for persisting timestamps persist `Instant`s, not `LocalDateTime`s,
  i.e. somehow tie the timestamp to a zone. However, some databases have limited support for such types
  (which has no zone information) or other quirks, making "always store in UTC" a better alternative.
-Databases that always persist in UTC are: ...TODO
-To force ..
+Currently, only PostgreSQL and Oracle rely on the database preserving time zone information,
+other databases store timestamps in UTC. **NB:** For backwards compatibility, the default behavior
+for "unknown" databases is to assume the database preserves time zone. For "known" databases,
+see the class `AutodetectJdbcCustomization`.
 
 :gear: `.enableImmediateExecution()`<br/>
 If this is enabled, the scheduler will attempt to hint to the local `Scheduler` that there are executions to be executed after they are scheduled to

db-scheduler/src/main/java/com/github/kagkarlsson/scheduler/jdbc/AutodetectJdbcCustomization.java

@@ -79,6 +79,18 @@ public AutodetectJdbcCustomization(DataSource dataSource, boolean persistTimesta
                   + "to be of type compatibe with 'TIMESTAMP WITH TIME ZONE', i.e. zone is persisted."
                   + " If not, consider overriding to always UTC via '.alwaysPersistTimestampInUTC()'.");
         }
+      } else {
+        if (persistTimestampInUTC) {
+          LOG.info(
+              "No database-specific jdbc-overrides applied. Behavior overridden to always store "
+                  + "timestamps in zone UTC");
+        } else {
+          Logger silencableLogger = LoggerFactory.getLogger(LOG.getName() + ".utc_warning");
+          silencableLogger.warn(
+              "No database-specific jdbc-overrides applied. Assuming time-related columns "
+                  + "to be of type compatibe with 'TIMESTAMP WITH TIME ZONE', i.e. zone is persisted."
+                  + " If not, consider overriding to always UTC via '.alwaysPersistTimestampInUTC()'.");
+        }
       }
 
     } catch (SQLException e) {