Which Are the Four Parts of 12 Bytes ObjectId Data Type?


Scott Campbell

Which Are the Four Parts of 12 Bytes ObjectId Data Type?

The ObjectId data type is a unique identifier commonly used in databases, particularly in MongoDB. It is a 12-byte value that consists of four different parts. Understanding these parts is essential for working with ObjectId data types effectively.

1. Timestamp

The first part of the ObjectId is a 4-byte timestamp value representing the creation time of the ObjectId in seconds since the Unix epoch (January 1, 1970, UTC). This allows for sorting and indexing based on creation time.

2. Machine Identifier

The next three bytes of the ObjectId represent the machine identifier.

It identifies the machine or process that generated the ObjectId. This helps ensure uniqueness even when multiple machines are generating ObjectIds concurrently.

3. Process Identifier

The following two bytes indicate the process identifier (PID) of the machine or process that created the ObjectId. Similar to the machine identifier, this helps guarantee uniqueness when multiple processes are generating ObjectIds simultaneously on a single machine.

4. Counter

The final three bytes of an ObjectId consist of a counter value.

This value increments each time an ObjectId is generated within a given second by a specific machine and process combination. The counter ensures that even if two ObjectIds are created within the same second by the same machine and process, they will still have distinct values.

In summary, an ObjectId data type has four parts: timestamp, machine identifier, process identifier, and counter. These parts work together to create a unique identification system that allows for efficient sorting and indexing while ensuring uniqueness across machines and processes.

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