acid

Haskell: Yesod and state

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问题 I was reading through the code for a Toy URL Shortener. However, there's significant parts I just can't get my head around. It has the following code: data URLShort = URLShort { state :: AcidState URLStore } For testing purposes, I wrote something like this in my own app: data MyApp = MyApp { state :: Int } I could then compile by changing main = warpDebug 3000 MyApp to main = warpDebug 3000 (MyApp 42) And I could then do reads of the state in handlers by doing mystate <- fmap state getYesod

How is Oracle ACID compliant when it does not honour 'isolation' property fully?

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问题 Claim: Oracle does not honour isolation property in ACID properties. As per Wikipedia page on ACID "Isolation ensures that concurrent execution of transactions leaves the database in the same state that would have been obtained if the transactions were executed sequentially." This can happen only if the transactions are serializable. Yes, Oracle has a transaction level called Serializable but it is not true serializability and is only snapshot isolation. Read https://blog.dbi-services.com

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数据库的ACID性质：原子性（ATOMIC）整个事务中的所有操作，要么全部完成，要么全部不完成，不可能停滞在中间某个环节一致性（Consistency）在事务开始之前和事务结束以后，数据库的完整性约束没有被破坏隔离性（Isolation）两个事务的执行是互不干扰的，一个事务不可能看到其他事务运行时中间某一时刻的数据持久性（Durability）在事务完成以后，该事务所对数据库所作的更改便持久的保存在数据库之中，并不会被回滚。来源： CSDN 作者：大耗咂链接： https://blog.csdn.net/qq_38029158/article/details/103654011

How exactly do transactions with PHP PDO work with concurrency?

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问题 I'm making a webapp where they'll be multiple users interacting with each other and reading/making decisions on/modifying shared data. I've read that transactions are atomic, which is what I need. However, I'm not sure how it works with the PHP PDO::beginTransaction() I mean atomic as in if one transaction is editing some data, all other transactions also modifying/reading that data will need to wait until the first transaction finishes. Like I don't want two scripts reading a value,

How To Implement ACID Transactions in Loopback

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问题 We've been trying to implement ACID transactions in Loopback without success. The only examples in the documentation use the 'create' method.We've tried completely overriding the events as well as multiple variations of Operation Hooks. We have only been able to get the create example to work. Core Requirement : We need to be able to start a transaction in the create and update methods for a specific model and then update multiple tables in the transaction (either using Loopback's ORM

Memory Mapped files and atomic writes of single blocks

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问题 If I read and write a single file using normal IO APIs, writes are guaranteed to be atomic on a per-block basis. That is, if my write only modifies a single block, the operating system guarantees that either the whole block is written, or nothing at all. How do I achieve the same effect on a memory mapped file? Memory mapped files are simply byte arrays, so if I modify the byte array, the operating system has no way of knowing when I consider a write "done", so it might (even if that is

从ACID到CAP到BASE

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学习思路 CAP理论 BASE理论应用场景 ACID相关请看《 ACID-本地事务-分布式事务》一、CAP理论 C(一致性)：分布式系统中所有备份节点的数据任何时间都保持一致（从任何一个节点取到的数据都一样） A(可用性)：系统在任何情况下（发生故障）都仍然可以对外提供服务（高可用） P(分区容错性)：如果数据产生了不一致的情况或者始终高可用，那么肯定存在分区（我们所有的线上服务都是集群部署）一致性和可用性是我们设计的目标，但就目前的系统设计来说分区容错性又是不可避免的，下面我们单独分析CA、CP、AP CA：放弃分区容错意味着是单机服务，宕机概率大，一旦宕机后整个服务不可用（线上避免） CP：放弃可用性，保证数据一致性和分区容错，意味着我们在做数据同步（一致性）的时候系统可能一直处于等待，直至所有数据一致（比如我们之前说的分布式事务2PC、3PC） AP：放弃一致性，意味着数据在短时间内可能是不一致的，但一直能对外服务就现阶段的微服务架构设计中CA很明显不符合，因此我们将在CP和AP中根据不同场景分别设计我们比较熟悉的zookeeper是CP系统，eureka是AP系统这里联想到为什么eureka比zookeeper更适合做注册中心：eureka是去中心化设计，每个节点都可以单独对外读写，数据同步可能出现短暂时间差，但zk是leader负责写并同步其它节点

Dirty Reads in SQL Server AlwaysOn

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问题 I have a pair of SQL Server 2014 databases set up as a synchronous AlwaysOn availability group. Both servers are set to the Synchronous commit availability mode, with a session timeout of 50 seconds. The secondary is set to be a Read-intent only readable secondary. If I write to the primary and then immediately read from the secondary (via ApplicationIntent=ReadOnly ), I consistently read dirty data (i.e. the state before the write). If I wait for around a second between writing and reading,

MySQL - Mutual exclusion in transactions and locks?

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问题 I am currently learning about MySQL's transaction and lock features. Are transactions with the isolation-level SERIALIZABLE and statements between a LOCK and UNLOCK statement on the same table executed mutually exclusive? EDIT 1 : For the transaction thing with isolation level SERIALIZABLE , is it even possible to determine whether the transaction is actually mutually exclusive or just the requirements like no phantom reads are fulfilled? Or do these two properties imply the same behavior?

Loopback: Atomic read and update

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问题 is there a way to implement something like this in loopback? LOCK READ INCREMENT UNLOCK I would like to keep counters as database values, each key is a counter (or a setting), and they shouldn't accessed my multiple requests at the same time. Also this should work for local requests too (no remoteHooks) Thanks 回答1: If you are using the mongoDB connector, this is supported by extended operators. MyModel.updateAll( { id: 123' }, { '$inc': { myproperty: 1 }}, // increment myproperty by 1 {