[MongoDB] MongoDB's missing knowledge points and mongodb's missing knowledge points

[MongoDB] MongoDB's missing knowledge points and mongodb's missing knowledge points

Up to now, I have read three mongodb books. Today, when I read the MongoDB authoritative guide by Kristina Chodorow in the United States, I found that there are still many omissions in my knowledge. Now I want to make a supplement;

I. Deletion speed

Deleting a document is usually fast, but it is slow to clear the entire set. Using drop to directly Delete the set is faster;

Now we have created more than 10 million test records:

 

Use db. tester. drop () instead of remove and findone, the speed is improved but there is a cost. No query conditions can be specified. The entire set is deleted, and all metadata is lost. After removing, the indexes remain unchanged;

2. Return array elements

If you know the subscript of an element, "$ slice" is very useful. But sometimes we want to return any array element that matches the query condition. Initialize a record to describe slice usage: