You need to create a new transaction table in Cloud Spanner that stores product sales data. You are deciding what to use as a primary key. From a performance perspective, which strategy should you choose?
A. The current epoch time
B. A concatenation of the product name and the current epoch time
C. A random universally unique identifier number (version 4 UUID)
D. The original order identification number from the sales system, which is a monotonically increasing integer
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Answer C
https://medium.com/google-cloud/cloud-spanner-choosing-the-right-primary-keys-cd2a47c7b52d
As per spanner documentation, monotonically increasing primary keys creates hotspot problems, that means all the inserts will be redirected to single server. In addition to that, UUID V4 is one of the recommended technique as per documentation.