isolation-level | 易学教程

Can't see rows inserted by a running transaction when isolation level is READ_UNCOMMITTED

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问题 I have applications that insert rows into table A concurrently. Each application inserts rows in batch mode (using a JDBC prepared statement) using a single transaction per batch (to avoid rebuilding index after each INSERT ). The rows present in each batch are completely independent, the transaction is used only for optimization. Each inserted row has its primary key set automatically ( AUTO_INCREMENT ). I have another application that processes the rows from table A based on their IDs. The

Default SQL Server IsolationLevel Changes

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问题 we have a customer that's been experiencing some blocking issues with our database application. We asked them to run a Blocked Process Report trace and the trace they gave us shows blocking occurring between a SELECT and UPDATE operation. The trace files show the following: The same SELECT query is being executed at different isolation levels. One trace shows a Serializable IsolationLevel while a later trace shows a RepeatableRead IsolationLevel. We do not use an explicit transaction while

ReadUncommitted broken in SQLite against NHibernate

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问题 I am using sqlite for test cases in a project that leverages NHibernate. Everything is working great, except when I try to create a ReadUncommitted transaction: e.g. Session.BeginTransaction(System.Data.IsolationLevel.ReadUncommitted) The error message is: "isolationLevel" (thats it) The call stack looks like: at System.Data.SQLite.SQLiteConnection.BeginDbTransaction(IsolationLevel isolationLevel) at System.Data.Common.DbConnection.System.Data.IDbConnection.BeginTransaction(IsolationLevel

Mixing isolation levels in PostgreSQL

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问题 Does it matter for a SERIALIZABLE transaction if any other session uses e.g. autocommit or the READ COMMITED isolation level? In other words is there any danger in mixing isolation levels (& autocommit) when accessing a database from multiple processes/threads (or anything else to watch out for)? Note that I'm aware of the "ordinary" issues, like SERIALIZABLE transactions asking for a retry etc. I'm asking for anything non-obvious that can happen when one is mixing different isolation levels.

Does H2 support the serializable isolation level?

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问题 Wikipedia describes the Phantom read phenomenon as: A phantom read occurs when, in the course of a transaction, two identical queries are executed, and the collection of rows returned by the second query is different from the first. It also states that with serializable isolation level, Phantom reads are not possible. I'm trying to make sure it is so in H2, but either I expect the wrong thing, or I do a wrong thing, or something is wrong with H2. Nevertheless, here's the code: try(Connection

How can you see what transaction isolation level an arbitrary oracle session is using

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问题 I am trying to find out what isolation level a particular session (not my own) has on an oracle server. Is there a v$.. view to get this? 回答1: You can test bit 28 in the flag column in v$transaction [1]. SELECT s.sid, s.serial#, CASE BITAND(t.flag, POWER(2, 28)) WHEN 0 THEN 'READ COMMITTED' ELSE 'SERIALIZABLE' END AS isolation_level FROM v$transaction t, v$session s WHERE t.addr = s.taddr AND s.sid = :sid AND s.serial# = :serial; Just remember that v$transaction only lists active transactions

Best Isolation Level to avoid deadlocks using an UPDATE sentence in Sql Server 2005

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问题 i need execute un update statement over an sql server table, this table is used by another process at the same time. because that sometimes deadlocks ocurs. wich Isolation Level do you recomend to avoid or minimize this deadlocks? 回答1: READ UNCOMMITTED But that allows the process to read the data before a transaction has committed, what is known as a dirty read. Further Reading You may prefer to turn on row versioning, the update creates a new version of the row and any other select

Change isolation level in individual ADO.NET transactions only

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问题 What is the best way to implement different isolation levels for individual transactions when using a client framework, ORM or similar to build queries, which does not support query hints like WITH(NOLOCK)? Imagine an application which uses ReadUncommitted level for a number of complex and long running queries (well aware of the related risks), and it is supposed to run with NHibernate and it's query criteria (or QueryOver/LINQ, just no string concatenation!). NHibernate doesn't support the

Concurrency strategy configuration for JBoss TreeCache as 2nd level Hibernate cache

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问题 I am using JBoss EAP 4.3. I'm currently looking into the different options for concurrency strategy when using the built-in JBoss TreeCache as a second level cache for Hibernate. I have set it up and I have verified that the cache is working by looking into the logs, but I am not sure what concurrency strategy is really used and how it is intended to work. For each Entity, I can set one of the following "usage" values in the @Cache annotation: NONE , READ_ONLY , NONSTRICT_READ_WRITE , READ

Two threads reading from the same table:how do i make both thread not to read the same set of data from the TASKS table

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I have a tasks thread running in two separate instances of tomcat. The Task threads concurrently reads (using select) TASKS table on certain where condition and then does some processing. Issue is ,sometimes both the threads pick the same task , because of which the task is executed twice. My question is how do i make both thread not to read the same set of data from the TASKS table I think you need have some variable (column) where you keep last modified date of rows. Your threads can read same set of data with same modified date limitation. Edit: I did not see "not to read" In this case you