Therefore, before we insert a new row into tbl Papers, we need to ensure that it’s going to be unique.Now open two new query windows and insert the following query text into both of them: In SQL Server 2005/2008, READ COMMITTED is the default transaction level - we’re being explicit about using the SERIALIZABLE isolation level, however. This is an expert feature, intended for use by those who thoroughly understand its consequences.

Wait behaviour and conflict reporting depend on the transaction parameters specified in the TPB block: If a record is modified by any transaction that was committed since the transaction attempting to get explicit lock started, or an active transaction has performed a modification of this record, an update conflict exception is raised immediately.

If the record is modified by any transaction that has committed since the transaction attempting to get explicit lock started, an update conflict exception is raised immediately.

It becomes possible, then, that a lock which appeared to succeed when requested will nevertheless , when an attempt is made to fetch a row which becomes locked by another transaction.

As the engine considers, in turn, each record falling under an explicit lock statement, it returns either the record version that is the most currently committed, regardless of database state when the statement was submitted, or an exception.

We will then look at ways to ferret out these issues and to resolve them before they sneak out the door with your finished product.

Armed with this understanding of the enemy and how it relates to your application, youll be much better able to avoid disaster. Scope The breadth and depth of this topic necessitates that scope be constrained.An API website, exposing a series of webservices, had been working fine for months, until I decided to run my client app with a lot more threads than usual.The tbl Papers table contains a number of entities, and each of them must have a unique Url value.Any idea why Pervasive does not like the FOR UPDATE?Deadlocks in any database can be a hard beast to weed out, especially since they may hide latently in your code, awaiting that specific moment when they explode.clause succeeds, it will secure a lock on the selected rows and prevent any other transaction from obtaining write access to any of those rows, or their dependants, until your transaction ends.