Difference between alert log and archive log in oracle databases I don't know anything about oracle databases. Actually I'm asking this question for my friend (He currently doesn't have access to internet!).

He wanted to know that what's the difference between alert logs and archive logs in oracle databases? Actually here is the scenario: There was a database for which auditing by alert logs is disabled. Someone came and truncated some data from this database. My friend didn't notice that because auditing by alert logs was disabled. But an oracle expert managed to find information about those transactions by looking at archive logs.

Now what I want to know is that: What type of information is stored in each of alert logs and archive logs? and under what conditions?

I searched documentations of oracle but unfortunately couldn't find anything. The only thing I found was mandatory auditing. But in mandatory auditing information about transactions and changes to the database isn't stored.

Thanks.
Alert log is a database log file where you can find various messages about your database, like time of startup, some db parameters, log file switch, possible errors that can occur etc.

Archive logs are archived redo(online) log files. In redo log files are all changes that happened to your data. If your database is in archivelog mode, than redo logs can't be overwritten, they are archived in some other location when they are full. Redo and archive logs are used in various database recovery scenarios.

So your Oracle expert probably used LogMiner(or some similar tool) to search through archive log files to find something like truncate table some_table;