Help me explain the content structure of this log file

【本文示例：MongoDB Log File】

  MongoDB logs provide a wealth of information about the operation and performance of the database. If you open the mongod.log (or whatever your log file is named), you’ll typically encounter several types of log entries. Here’s an explanation of the typical content structure:

1. Timestamp: Each log entry starts with a timestamp, indicating when the event occurred. This is crucial for troubleshooting as it allows you to correlate database events with other system events.

   2023-09-21T07:32:14.896+0000
   

2. Severity Level: After the timestamp, there’s a severity level indicating the nature of the log entry. Common levels include:

   • I - Informational
   • W - Warning
   • E - Error
   • F - Fatal

   I CONTROL
   

3. Component: This indicates the database component or module associated with the log entry. Examples include:

• CONTROL for messages related to the control processes.
• NETWORK for network-related events.
• STORAGE for storage events.
• QUERY for query operations.

4. Message: The actual log message detailing the event or the issue. The message might be straightforward or could require some MongoDB-specific knowledge to interpret.“WiredTiger message”: This is a brief description of the log. MongoDB uses the WiredTiger storage engine by default, and this message indicates that what follows is a message generated by WiredTiger.

   [initandlisten] MongoDB starting : pid=12345 port=27017 dbpath=/data/db 64-bit host=myServer
   

5. Connection Identifier: For entries related to client connections, there might be a connection identifier which indicates which client connection the log entry is associated with.

   [conn12345] end connection 192.168.1.100:54922 (8 connections now open)
   

6. Stack Traces: In cases of errors or crashes, you might find stack traces in the log. These are more verbose entries that provide a snapshot of the call stack at the time of the event. Stack traces are valuable for in-depth troubleshooting or when seeking support from MongoDB developers or the community.

7. Performance Statistics and Metrics: Especially if the database profiler is enabled, you might find detailed performance metrics about query execution times, page faults, and other critical performance metrics.

8. Message Identifier (id): 22430: This is a unique identifier for this specific type of log message. MongoDB uses these IDs to uniquely categorize different types of messages. When troubleshooting or discussing specific log messages with the MongoDB community or support, this ID can be referenced.

9. Context (ctx): “Checkpointer”: This gives context about what part or process within the component was active or responsible when the log was written. In this case, the Checkpointer context suggests this log pertains to checkpointing activities in MongoDB, which are essential for ensuring data durability and consistency.

10. Attributes (attr): The attributes provide more detailed information corresponding to the message.

    • “message”:“[1695292446:647416][790:0x7f4094e03700], WT_SESSION.checkpoint: [WT_VERB_CHECKPOINT_PROGRESS] saving checkpoint snapshot min: 20754, snapshot max: 20754 snapshot count: 0, oldest timestamp: (0, 0) , meta checkpoint timestamp: (0, 0) base write gen: 2878047”:
    • This message from WiredTiger provides details about a checkpoint operation, including:
      • Checkpoint progress (WT_VERB_CHECKPOINT_PROGRESS)
      • Snapshot information (min, max, and count values)
      • Timestamp details (oldest timestamp, meta checkpoint timestamp)
      • A base write generation number (base write gen)

  Remember, the exact content and the verbosity of the logs can vary depending on your MongoDB configuration. For example, adjusting the log verbosity level can either increase or decrease the amount of information captured in the log.

  When troubleshooting, it’s often helpful to have a good understanding of the log structure, as it enables you to quickly pinpoint potential issues or understand the operational flow of your MongoDB server.