In this lesson, we’ll learn how TrueTime guarantees correctness properties around concurrency control In information technology and computer science, especially in the fields of computer programming, operating systems, multiprocessors, and databases, the concurrency control ensures that correct results for concurrent operations are generated, while getting those results as quickly as possible. [source: Wikipedia]and how those properties ensure the following:

1. Externally consistentExternal consistency is a property of transaction-processing systems, where clients dynamically synthesize transactions that contain multiple read and write operations on arbitrary objects. [source: Google Cloud] transactions

2. Reads from the past that do not block any ongoing transaction

3. Read-only transactions that do not require any lock

These features make it possible to ensure that at any time, t, the full database audit read will see the exact results of all transactions that are committed as of t.

We will use Paxos write and Spanner clients write to differentiate between both writes.

Timestamp management

The implementation of Spanner supports reads from a snapshot and read-only and read-write transactions. The system implements the read-write transactions as standalone writes, whereas the read-only transactions are implemented as non-snapshot standalone reads. The following table shows the operation types Spanner supports and their respective concurrency control.

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