store Optimized for performance Support for arbitrary data Key-based access Multi-key operations Atomicity of both operations and transactions Data expiration Characteristics of Redis Eviction policies

such as mutexes and semaphores. ✓ Don’t use volatile objects for inter-thread communication. ## Atomicity Not Guaranteed ■ Accesses to volatile objects are not guaranteed to be atomic. In other words object can potentially result in a data race. ■ As an example, consider the following code... ## Atomicity Not Guaranteed - Suppose that this code is executing on thread A on a platform where a double is marked #2. ■ If it does, B might observe v as having a value that is neither 8.67 nor 53.09. ## Atomicity Not Guaranteed ## Miscompiled volatiles? ■ Eide and Regehr [2008] tested 13 versions of 5 distinct

ACID writes for a single shard. Support is underway for cross-shard Atomic transactions. As for atomicity, the following levels are supported: • SINGLE: disallow multi-db transactions. • MULTI: multi-db guarantees. With this addition, Vitess can be configured to support the following three levels of atomicity: 1. Single database: At this level, only single database transactions are allowed. Any transaction it is a separate option instead of being always on. ## I solation 2PC transactions guarantee atomicity: either the whole transaction commits, or it is rolled back entirely. It does not guarantee Isolation

ACID writes for a single shard. Support is underway for cross-shard Atomic transactions. As for atomicity, the following levels are supported: • SINGLE: disallow multi-db transactions. • MULTI: multi-db guarantees. With this addition, Vitess can be configured to support the following three levels of atomicity: 1. Single database: At this level, only single database transactions are allowed. Any transaction it is a separate option instead of being always on. ## I solation 2PC transactions guarantee atomicity: either the whole transaction commits, or it is rolled back entirely. It does not guarantee Isolation

Finalize and Cleanup ..... 363 Shard Isolation and Atomicity Model ..... 364 Introduction ..... 364 Cross-shard isolation ..... 364 Cross-shard atomicity ..... 365 In closing ..... 368 Tracing .. main row. These essentially result in distributed transactions, which require 2PC to guarantee atomicity. There have been requests to see if we can avoid 2PC and find a solution that could still give ACID writes for a single shard. Support is underway for cross-shard Atomic transactions. As for atomicity, the following levels are supported: • SINGLE: disallow multi-db transactions. • MULTI: multi-db

Linearizable: No (or Yes with k-LIFO) Quantifiable: Yes Conditional Semantics Violates Type Constraints, Atomicity Conditional pop assumed to make $ H_{2} $ Linearizable. $$ \begin{array}{l}\mathsf{P0}\quad\left|\frac{x Identify an instruction in which the entire effects of the method become visible Demonstrates: Atomicity Isolation ## Method Call Conservation ## Proof by cases to demonstrate A method call completes jpg) Figure 6: Negative stack formed @timeB after 3 push followed by 5 pop calls. ## Providing Atomicity Compare-And-Swap (CAS) atomically updates an object given an expected value. If the expected value

Serialization: Strict global order or relaxed per producer order API: single item / multiple items, atomicity-ready or not • Message size: fixed / dynamic Queue - push(back / tail), pop(front / head) - Busy atomic<> implementation supports atomicity by the CPU platform, than std::atomic:is_always_lockfree will be true. The queue requires hardware atomicity, if it is not available from the compile

ACID writes for a single shard. Support is underway for cross-shard Atomic transactions. As for atomicity, the following levels are supported: • SINGLE: disallow multi-db transactions. • MULTI: multi-db guarantees. With this addition, Vitess can be configured to support the following three levels of atomicity: 1. Single database: At this level, only single database transactions are allowed. Any transaction it is a separate option instead of being always on. ## I solation 2PC transactions guarantee atomicity: either the whole transaction commits, or it is rolled back entirely. It does not guarantee Isolation

main row. These essentially result in distributed transactions, which require 2PC to guarantee atomicity. There have been requests to see if we can avoid 2PC and find a solution that could still give ACID writes for a single shard. Support is underway for cross-shard Atomic transactions. As for atomicity, the following levels are supported: • SINGLE: disallow multi-db transactions. • MULTI: multi-db guarantees. With this addition, Vitess can be configured to support the following three levels of atomicity: 1. Single database: At this level, only single database transactions are allowed. Any transaction

如果准备过程中出现问题，可以回滚 • 提交阶段不允许出错 • 资源层面提供保障业务侵入性低 • 协议成本高，并且存在全局锁的问题 ## ACID 与 BASE • ACID （刚性事务） • 原子性 (Atomicity) • 一致性 (Consistency) - 隔离性 (Isolation) - 持久性 (Durability) - BASE (柔性事务) • 基本可用（Basically 2/1/9/5/21954dd3fc87fbdb89d08f0e9bd8b79f/p17_2.jpg) 保留所有事务数据! ## ACID 与 Saga • ACID • 原子性 (Atomicity) • 一致性 (Consistency) - 隔离性 (Isolation) - 持久性 (Durability) • Saga只提供ACD保证 • 原子性（通过Saga协调器实现）