Factors Affecting Uniqueness
While BSON Object IDs are designed to be unique, there are rare scenarios where duplicates can occur. These below scenarios include:
- Counter Overflow: If more than 16,777,216 (2^24) documents are inserted in a single second on the same machine and process then the counter may overflow and potentially leading to duplicate IDs.
- Non-Incrementing Counters: Some MongoDB drivers use random numbers for the counter portion of the BSON Object ID instead of incrementing values. This can lead to a 1 in 16,777,216 chance of generating a non-unique ID if two IDs are generated in the same second on the same machine and process.
- Machine and Process Hash Collision: In rare cases, the machine identifier and process identifier may map to the same values for two different machines. If this occurs, and the counters on the two machines generate the same value during the same second, duplicate IDs can be generated.
What are the Possibility of Duplicate Mongo ObjectId’s in Two Different Collections?
MongoDB’s BSON Object IDs are important for uniquely identifying documents within collections. While these IDs are designed to be unique within a collection there is often confusion about their uniqueness across different collections.
In this article, we will learn about the factors that determine the Probability of duplicate MongoDB Object IDs being generated in two different collections.