what are the trace logs and uls logs in sharepoint ? are these are same logs? and which logs are saved in wss_logging database?
or
which logs are save in wss_logging database and what is the retention period to stay this logs in this database.
ULS - Unified Logging Service. SharePoint, it's services, and if implemented 3rd party application can use the ULS to write to the SharePoint trace log files. Each server keeps a copy of it's own logs.
In Central Admin under Monitoring you can configure the diagnostic information that is collecter, or use the Set-SPDiagnosticConfig cmdlet.
The WSS Logging database is used to farm logging information, this can include the ULS logs from each server, server event logs, farm health reports, usage data and possibly custom data from 3rd party applications and services. Default retention period is 14 days.
You can view and set what data is stored in the logging database with the Get-SPUsageDefinition and Set-SPUsageDefinition cmdlets.
Microsoft provides detailed information on both ULS and the logging database
ULS: https://msdn.microsoft.com/en-us/library/office/ff512738(v=office.14).aspx
Logging DB: https://technet.microsoft.com/en-us/library/hh769360(v=office.14).aspx
