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- Evaluate Performance of Current Operations
Evaluate Performance of Current Operations¶
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The following sections describe techniques for evaluating operational performance.
Use the Database Profiler to Evaluate Operations Against the Database¶
MongoDB provides a database profiler that shows performance characteristics of each operation against the database. Use the profiler to locate any queries or write operations that are running slow. You can use this information, for example, to determine what indexes to create.
For more information, see Database Profiling.
For MongoDB 3.6 deployments, starting in version 3.6.11, secondary
members of a replica set now log oplog entries that
take longer than the slow operation threshold to apply. These slow
oplog messages are logged for the secondaries in the
diagnostic log
under the REPL
component with the text applied op: <oplog entry> took <num>ms
.
These slow oplog entries depend only on the slow operation threshold.
They do not depend on the log levels (either at the system or component
level), or the profiling level, or the slow operation sample rate. The
profiler does not capture slow oplog entries.
Use db.currentOp()
to Evaluate mongod
Operations¶
The db.currentOp()
method reports on current operations
running on a mongod
instance.
Use explain
to Evaluate Query Performance¶
The cursor.explain()
and db.collection.explain()
methods return information on a query execution, such as the index
MongoDB selected to fulfill the query and execution statistics. You can
run the methods in queryPlanner
mode, executionStats mode, or
allPlansExecution mode to
control the amount of information returned.
Example
To use cursor.explain()
on a query
for documents matching the expression { a: 1 }
, in the
collection named records
, use an operation that resembles the
following in the mongo
shell:
For more information, see Explain Results,
cursor.explain()
, db.collection.explain()
, and
Analyze Query Performance.