Handy tool for Sitecore Log

Sitecore is having matured logging mechanism which logged all kind of log from CMS and CD site

It's does provide different kind of mechanism to view the logs like:

• SCLA(Sitecore log Analyzer)
• Sitecore Admin tool for log 
• Application insight(PaaS only).

SCLA
 SCLA is very handy tool to view Sitecore generated logs. It provides different filter to view different kind of log. This tool is still got unofficial support till Sitecore 9.2 (on-premise).We can find very good documentation at Sitecore portal for Sitecore 9.3 onward (Azure based )  : Documentation .
I tried to explain on-premise Sitecore instance, the important part which we always look for during debugging.

1. First we need to map the log file path then click on Analyze button.
2. We can apply date filter or by default it's disabled.
3. We have different tab like Messages,Audit,Health Monitor,Raw View and Internal program Log
4. In Message tab you can there are four different check box for Error, Warnings,info, Fatal and Debugs.
5. Message is the tab most of the time developer use to view log. In Left side pane you can view all the consolidated list of error. Once you check the error type it will show on right side pane the detail stack trace of the error. In right side pane we have two tab one for multiple Messages and second for Single messages. Multiple messages shows all occurrence and Single message show the single instance. Here we can see the time stamp of the error log and once you click on the error you will get detail stack trace.Similar way we will have warning,info and fatal.
6. For Health Monitor we can view lot of information about cache,object size,heap memory, GC and CLR object

This is again important to analyse the application caching and performance. We can view the cache size,cache instance,cache count,private bytes in memory,process bytes,memory in heaps/GC.
7. Raw view gives the view of log the way it's being logged in log file

I am uploading the rar file of SCLA setup, we can find from google as well. just extract the file and click on exe file from here SCLA 

Administrator tool for Log
In Sitecore 9.x we got Administrator tool where we have options to view,download all different type of log files.

We got 12 different types of log files for different purposes:

1. Aggregation.log
2. Client.log
3. contactMergeDataUpgrade.log
4. Crawling.log
5. Eds.log
6. Exm.log
7. Fxm.log
8. log
9. Owin.log
10. Publishing.log
11. Search.log
12. SPE.log

We can click each one of them and view there list of files or we can download them.

Sitecore Log at Application Insights:

Sitecore writes log information to Microsoft Application Insights® when running on the Microsoft Azure® App Service.In Application Insights, you can identify error and warning messages, identify messages from specific roles and Sitecore instances, and search for specific log messages.

• Go to the Microsoft Azure Portal and log on.
• On the Dashboard, click All resources, and select your Sitecore installation from the list of provisioned Azure resources.
• Click the Application Insights resource. When the page opens, on the toolbar, click log and view Sitecore logs of its item and request based on query.

• In the Search panel that appears on the right side, type your key search words in the Search box and click Enter.

• We have different type of  tools in Application insight like :
• Application map
• Smart detection
• Live metrics
• Search
• Availability
• Failure
• Performance
• Troubleshooting

We can use these tools to view different kind of logging at application and server level.

All failure can be tracked based on time stamp or query:

 Find log messages by level of severity

Sitecore translates Log4net message severity levels into Application Insights Trace severity levels. The four supported severity levels are Error, Warning, Informational, and Verbose. For example, to search for Error and Warning messages only:

• In the Azure portal, at the top of the Search panel, click Filters.
• In the Filter panel that appears on the right side, expand the Severity level tab.
• Select the Error and Warning checkboxes.
• To see the log messages with severity levels of Error and Warning, at the bottom of the panel, click Update.

Reference : https://doc.sitecore.com/developers/93/sitecore-experience-manager/en/analyze-sitecore-logs-with-application-insights.html

https://marketplace.sitecore.net/en/Modules/Sitecore_Log_Analyzer.aspx