låseskalering

Låseskalering, or lock escalation, is a database concurrency control mechanism. It occurs when a database management system increases the granularity of locks it holds. Initially, a transaction might acquire many row-level locks on individual records within a table. If the number of these row-level locks becomes excessive, consuming significant memory or impacting performance, the database system may automatically escalate these locks to a page-level lock or even a table-level lock. This reduces the total number of locks the system needs to manage, thereby freeing up resources and potentially improving performance.

The primary motivation behind lock escalation is to manage the overhead associated with maintaining a large number of individual locks. Each lock requires memory and processing resources. When a transaction holds thousands or millions of row locks, this overhead can become substantial. Lock escalation consolidates these fine-grained locks into fewer, coarser-grained locks. For example, instead of holding locks on 1000 individual rows, the system might instead acquire a single lock on the entire table containing those rows.

While lock escalation can improve system performance by reducing lock overhead, it comes with a trade-off. Coarser-grained locks can increase the likelihood of lock contention and deadlocks. If a transaction escalates to a table lock, it prevents other transactions from accessing any part of that table, even if they only intended to modify a different row. Database systems typically have configurable thresholds that trigger lock escalation, allowing administrators to tune the system based on workload characteristics and available resources.