isolation-level

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. EDIT: From http://www.postgresql.org/docs/9.4/static/transaction-iso.html : Consistent use of

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 executing the query. The UPDATE query is being executed with a RepeatableRead isolation level but is

How do I set the isolation level of a transaction to 'SERIALIZABLE' in PHP using mysqli? I have looked everywhere and I can't find any information on it. Here is an explanation of the isolation levels. You can just set the isolation level in a query before you run your statements. This assume that you do everything using the same session: $mysqli = new mysqli('localhost', 'user', 'pass', 'db'); $mysqli->query("SET SESSION TRANSACTION ISOLATION LEVEL SERIALIZABLE"); ... You may also want to turn off autocommit before hand since it changes the way serializable isolation works . Short answer:

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 isolationLevel) at NHibernate.Transaction.AdoTransaction.Begin(IsolationLevel isolationLevel) If I switch

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 connection1 = DriverManager.getConnection(JDBC_URL, JDBC_USER, JDBC_PASSWORD)) { connection1

I have a function, that does multiple queries on the same dataset and I want to ensure all the queries would see exactly the same data. In terms of SQL, this means REPEATABLE READ isolation level for the databases that support it. I don't mind having higher level or even a complete lockdown if the database isn't capable. As far as I see, this isn't the case. I.e. if I run something like this code in one Python shell: with transaction.atomic(): for t in range(0, 60): print("{0}: {1}".format(t, MyModel.objects.count())) time.sleep(1) As soon as I do MyModel.objects.create(...) in another, the

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? The reading of a single 8k IO Page ? or until the the complete Select statement in which the lock was

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? 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 statements use the old version until this one has committed. To do this turn on READ_COMMITTED_SNAPSHOT mode. There

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 with(nolock) hint (except when using native SQL, which is currently used in many cases). So, in order to