isolation-level

问题 When SQL Server Books online says that "Shared (S) locks on a resource are released as soon as the read operation completes , unless the transaction isolation level is set to repeatable read or higher, or a locking hint is used to retain the shared (S) locks for the duration of the transaction." Assuming we're talking about a row-level lock, with no explicit transaction, at default isolation level (Read Committed), what does " read operation " refer to? The reading of a single row of data?

问题 As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, visit the help center for guidance. Closed 7 years ago . Does someone knows a good book where transaction isolation levels are explained with a lot of examples and advices in what case what

问题 I may be talking nonsense but: Which isolation level is "best" for lots of Threads running on lots of connections, executing lots of updates and writes using transactions? Or isolationlevels are only for reads? --EDIT DBMS ... InnoDB mysql... best.. well what i want is to run parallel transactions of writes/updates, and if for example we have two updates on the same Column, i do not whant to get concurrency problems... so parallel writes/updates, which all run with locking on the database -

问题 Assume I have a message relation where I save messages that was created with this command: CREATE TABLE message ( id serial primary key, foo1 integer, foo2 integer, foo3 text ) And we have a function that gets a message and deletes it from the relation, like this: CREATE FUNCTION get_and_delete_message(p_foo1 integer) RETURNS TABLE(r_id integer, r_foo1 integer, r_foo2 integer, r_foo3 text) AS $$ DECLARE message_id integer; BEGIN SELECT id INTO message_id FROM message WHERE foo1 = p_foo1 LIMIT

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

问题 I need to solve a resource reservation pattern with Spring and MariaDB. The problem is very simple, I have a guest table where I store guest names of events, I have to be sure that the guest count for the event must be less or equals the maximum capacity. This is the table: create table guest( event int, name varchar(50) ) create index event on guest (event); What is the right lock procedure and isolation level for DB? Please consider that this code will run in multi-threading container. I

问题 I would like to set isolation level using eclipse link, I tried these 2 ways to do it: java.sql.Connection mgr = EMF.get().createEntityManager(); tx = mgr.getTransaction(); tx.begin(); java.sql.Connection connection = mgr.unwrap(java.sql.Connection.class); connection.setTransactionIsolation(java.sql.Connection.TRANSACTION_READ_COMMITTED); System.out.println("Connection: "+connection.getTransactionIsolation()); //prints TRANSACTION_READ_COMMITED as expected org.eclipse.persistence.sessions

问题 I am working on DW project where I need to query live CRM system. The standard isolation level negatively influences performance. I am tempted to use no lock/transaction isolation level read uncommitted. I want to know how many of selected rows are identified by dirty read. 回答1: Maybe you can do this: SELECT * FROM T WITH (SNAPSHOT) EXCEPT SELECT * FROM T WITH (READCOMMITTED, READPAST) But this is inherently racy. 回答2: Why do you need to know that? You use TRANSACTION ISOLATION LEVER READ

问题 Closed . This question needs to be more focused. It is not currently accepting answers. Want to improve this question? Update the question so it focuses on one problem only by editing this post. Closed 9 months ago . I would like to know different isolation levels with respect to commit, and would also like to know about row-level and table-level lock. 回答1: ANSI/ISO SQL defines four isolation levels: serializable repeatable read read committed read uncommitted According to Oracle's Database

问题 I'm part of a team building an ADO.NET based web-site. We sometimes have several developers and an automated testing tool working simultaneously a development copy of the database. We use snapshot isolation level, which, to the best of my knowledge, uses optimistic concurrency: rather than locking, it hopes for the best and throws an exception if you try to commit a transaction if the affected rows have been altered by another party during the transaction. To use snapshot isolation level we