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Why does MongoDB lock both databases at the same time?
Therefore, MongoDB must lock both the collection’s database and the local database. The mongod must lock both databases at the same time to keep the database consistent and ensure that write operations, even with replication, are “all-or-nothing” operations.
Why does MongoDB use multi granularity locking?
MongoDB uses multi-granularity locking [ 1] that allows operations to lock at the global, database or collection level, and allows for individual storage engines to implement their own concurrency control below the collection level (e.g., at the document-level in WiredTiger).
What kind of concurrency control does MongoDB use?
Beginning with version 3.0, MongoDB ships with the WiredTiger storage engine. For most read and write operations, WiredTiger uses optimistic concurrency control. WiredTiger uses only intent locks at the global, database and collection levels.
What does renamecollection do in MongoDB 4.2?
Prior to MongoDB 4.2, the renameCollection command takes an exclusive (W) lock on the database when renaming within the same database. If renaming a collection within the same database, the renameCollection () method takes an exclusive (W) lock on the source and target collections.
What happens when there is a write conflict in MongoDB?
When the storage engine detects conflicts between two operations, one will incur a write conflict causing MongoDB to transparently retry that operation. Some global operations, typically short lived operations involving multiple databases, still require a global “instance-wide” lock.
When do you need to analyze MongoDB performance?
MongoDB Performance ¶ As you develop and operate applications with MongoDB, you may need to analyze the performance of the application and its database. When you encounter degraded performance, it is often a function of database access strategies, hardware availability, and the number of open database connections.