Is Read Uncommitted (NOLOCK) An Optimistic Or Pessimistic Isolation Level?

Poll Worker

I ran a Twitter poll recently, because as I was writing another blog post, I wasn’t quite sure how to group uncommitted/nolock between pessimistic or optimistic isolation levels.

Blocking on Columnstore Indexes that RCSI and NOLOCK Don’t Resolve

I recently ran into a production issue where a SELECT query that referenced a NOLOCK-hinted table was hitting a 30 second query timeout. Query store wait stats suggested that the issue was blocking on a table with a nonclustered columnstore …

Implicit Transactions: Why Unrelated Queries Block Each Other In SQL Server

A Bit Sensational

I don’t really mean that unrelated queries block each other, but it sure does look like they do.

Implicit Transactions are really horrible surprises, but are unfortunately common to see in applications that use JDBC drivers to …

Normalizing SQL Server Tables To Reduce Query Blocking


I see a lot of tables that look something like this:

CREATE TABLE dbo.orders
    order_id int NOT NULL PRIMARY KEY
         DEFAULT (NEXT VALUE FOR dbo.order_id),
    order_date datetime NOT NULL,
    order_ship_date datetime NOT NULL,
    order_total money NOT NULL,

Locking Hints Make Troubleshooting Blocking And Deadlocks Confusing In SQL Server

King Of The DMV

Many people will go their entire lives without using or seeing a lock hint other than NOLOCK.

Thankfully, NOLOCK only ever leads to weird errors and incorrect results. You’ll probably never have to deal with the …