What is TrueTime in spanner?

TrueTime is a highly available, distributed clock that is provided to applications on all Google servers1. … This guarantee holds across all servers and all timestamps. This feature of TrueTime is used by Cloud Spanner to assign timestamps to transactions.

What is TrueTime API?

TrueTime is an API available at Google that directly exposes clock uncertainty. Comparing to standard datetime libraries, instead of a particular timestamp, TrueTime’s now() function returns an interval of time [earliest, latest]. It also provides two functions: after(t) returns true if t has definitely passed.

What is Google true time?

TrueTime is a global reference clock with a bounded non-zero error. TrueTime utilizes satellite-connected GPS and atomic clocks. Google’s data centers are equipped with a series of GPS receivers and atomic clocks. With the launch of Amazon Time Sync Service, AWS regions are equipped with similar GPS and atomic clocks.

What is the difference between a read only transaction and a snapshot read in spanner?

Spanner supports read-write transactions, read-only transactions, and snapshot reads. Standalone writes are implemented as read-write transactions. Non-snapshot standalone reads are implemented as read-only transactions. A snapshot read is a read in the past that executes without locking.

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Does spanner violate CAP Theorem?

Spanner is Google’s highly available global-scale distributed database. It provides strong consistency for all transactions. This combination of availability and consistency over the wide area is generally considered impossible due to the CAP Theorem.

Is spanner eventually consistent?

Spanner is a strongly-consistent, distributed, scalable database built by Google engineers to support some of Google’s most critical applications. It takes core ideas from the database and distributed systems communities and expands on them in new ways.

What is externally consistent?

External consistency means having the same aesthetic design or performance across multiple systems. External consistency extends the benefits of internal consistency across multiple independent systems. … Ensure that systems are always internally consistent and externally consistent to the greatest degree possible.”

Does Google use atomic clock?

Google has gone a step further, installing its own atomic clocks — and GPS antennas — directly on its machines. The system was first used to help serve ads across the Google empire, but it has since expanded to all sorts of other Google services.

What is Linearizable consistency?

Linearizability is one of the strongest single-object consistency models, and implies that every operation appears to take place atomically, in some order, consistent with the real-time ordering of those operations: e.g., if operation A completes before operation B begins, then B should logically take effect after A.

What is external consistency spanner?

External consistency states that Cloud Spanner executes transactions in a manner that is indistinguishable from a system in which the transactions are executed serially, and furthermore, that the serial order is consistent with the order in which transactions can be observed to commit.

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What is the difference between Cloud SQL and Cloud spanner?

The main difference between Cloud Spanner and Cloud SQL is the horizontal scalability + global availability of data over 10TB. Spanner isn’t for generic SQL needs, Spanner is best used for massive-scale opportunities. 1000s of writes per second, globally.

What is Rdbms transaction?

A transaction is a single logical unit of work which accesses and possibly modifies the contents of a database. Transactions access data using read and write operations. In order to maintain consistency in a database, before and after the transaction, certain properties are followed.

What is read only transaction?

A READ ONLY transaction is a transaction in which the read consistency is set at the transaction level. In a READ ONLY transaction, a logical snapshot of the database is created at the beginning of the transaction and released at the end of the transaction.

What is CAP theorem in Mongodb?

CAP stands for Consistency, Availability and Partition Tolerance. Consistency means, if you write data to the distributed system, you should be able to read the same data at any point in time from any nodes of the system or simply return an error if data is in an inconsistent state.