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What is an IX lock?
The locking system grants an intent exclusive (IX) or intent shared (IS) lock at the table level before it grants an exclusive (X) or shared (S) lock on a page in a table. An IX lock at table level indicates that pages have been updated, a IS lock at table level indicates that pages have been read.
Can a SELECT query lock the database?
Yes, select locks the table until reads completes which conflicts with Insert/Delete/Updates lock mode. Generally Select should be used with WITH (NOLOCK) to avoid blocking the dml operations but it will result in dirty reads. You will need to weigh between concurrency and data consistency.
What is IX SQL?
Regular intent locks: Intent exclusive (IX) – when an intent exclusive lock (IX) is acquired it indicates to SQL Server that the transaction has the intention to modify some of lower hierarchy resources by acquiring exclusive (X) locks individually on those lower hierarchy resources.
Is IX a 6?
Lock modes Intentional locks include “intention shared” (IS), “intention exclusive” (IX), and the combined “shared and intention exclusive” (SIX) locks. IS locks conflict with X locks, while IX locks conflict with S and X locks.
What is lock type?
A physical lock is used and released within a transaction. The locking system uses physical locks to synchronize access to resources. Control. An internal lock type that manages a table while its schema is being changed or loaded. This lock is always a physical lock.
When does a simple SELECT query acquire a lock?
However there are ways to bypass this (SQL Server has the nolock hint). If the statement is not in a BEGIN TRAN the lock is released after the SELECT statement has run. It is a common misconception that a SELECT query running at the default READ COMMITTED transaction isolation level will always take shared locks to prevent dirty reads.
Can a shared lock block a SELECT query?
The SELECT will not block, and it will not read any “dirty” un-committed data – but it might skip some rows, e.g. not show all your rows in the table. On performance you keep focusing on select. Shared does not block reads. Shared lock blocks update.
What’s the difference between a select and no lock?
Versus a SELECT WITH (NOLOCK)? A SELECT in SQL Server will place a shared lock on a table row – and a second SELECT would also require a shared lock, and those are compatible with one another. So no – one SELECT cannot block another SELECT.
Where are the locks in the IX table?
EDIT: Actually, it seems that the locks are on two pages of IX_Table2 – the one where the key used to be, and the one where it needs to be after the change. The two locks are taken in a sequence, and in a different order from the select.