MongoDB Learning Notes Analyzer and explain

MongoDB Analyzer:

To detect if the MongoDB parser is open:

Db.getprofilinglevel ()

• 0 indicates no open
• 1 means open, and if the query execution time exceeds the maximum query execution time for the second parameter in milliseconds (ms), it is logged or ignored.
• 2 means open, and all query statements are logged

Db.setprofilinglevel (2)

A System.profile collection is found in the test database at this point: but this collection is still empty.

Then we make a query Db.comments.find ({timestamp:6})

Then query the collection: Db.system.profile.find (). Pretty (), we can see the execution plan of the query just now.

"nreturned": 1 returns the number of rows 1

"Millis": 0 Execution time

"Stage": "Collscan" not used Index

"docsexamined": 81 scan of 8 documents

Thus, we can pass the statement: Db.system.profile.find ({"Query.find": "Comments"}). Sort ({"TS":-1}). Limit (1). Pretty () Queries out the latest execution plan in the specified statement.

System.profile The default size of the collection is 1024KB=1MB, let's expand its size:

1. Close the MongoDB parser
2. Delete System.profile Collection
3. Create 50M fixed-size collections

MongoDB explain:

Analyze a specific query with explain

Db.comments.find ({timestamp:6}). Explain (true)

MongoDB Learning Notes Analyzer and explain