![]() It doesn’t group operations together into transactions, so it does not prevent problems such as write skew, unless you take additional measures such as materializing conflicts.Ĭloud Spanner provides external consistency, which is a stronger property than linearizability, because linearizability does not say anything about the behavior of transactions.Īll accesses are seen by all parallel processes (or nodes, processors, etc.) in the same order (sequentially)5 Linearizability is a recency guarantee on reads and writes of a register (an individual object). It's okay for that serial order to be different from the order in which transactions were actually run.Ĭloud Spanner provides external consistency, which is a stronger property than serializability, which means that all transactions appear as if they executed in a serial order, even if some of the reads, writes and other operations of distinct transactions actually occurred in parallel. It guarantees that transactions behave the same as if they had executed in some serial order. Serializability is an isolation property of transactions, where every transaction may read and write multiple objects. All transactions across a Cloud Spanner database satisfy this consistency property, not just those within a replica or region. Any data written to the database must be valid according to all defined rules.Ĭloud Spanner provides external consistency, which is strong consistency + additional properties (including serializability and linearizability). Below is a short primer on consistency:Ĭonsistency in database systems refers to the requirement that any given database transaction must change affected data only in allowed ways. A quick look at different databases on the market shows that not all consistency models are created equal, and that some of the related terms can intimidate even the bravest database developer. ![]() Put another way, data stores that provide transactions and consistency across the entire dataset by default lead to fewer bugs, fewer headaches and easier-to-maintain application code.ĭefining database consistencyBut to have an interesting discussion about consistency, it’s important to first define our terms. To quote the original Spanner paper, “we believe it is better to have application programmers deal with performance problems due to overuse of transactions as bottlenecks arise, rather than always coding around the lack of transactions.” 1 One of the things we’ve learned here at Google is that application code is simpler and development schedules are shorter when developers can rely on underlying data stores to handle complex transaction processing and keeping data ordered. Do you like complex application logic? We don’t either.
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