MognoDB what KeysExamined means?

user_10022763 0
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MongoDB .explain("executionStats") shows keysExamined of something around 103,000 but I cant find out what it means.

mongodb
2 Answers

From MongoDB docs:

explain.executionStats.totalKeysExamined

Number of index entries scanned. totalKeysExamined corresponds to the nscanned field returned by cursor.explain() in earlier versions of MongoDB.

user_143898300

  1. This are good news when you have totalKeysExamined > 0 , this mean your query is using index. Here it is important to understand what is the size of your database , index selectivity , frequency and use case of this query to be identified if 103,000 is a good examination number for your search.

  2. If you have totalKeysExamined = 0 , and totalDocsExamined > 0 than you may need to create some indexes.

  3. The best case is when you have totalDocsExamined = 0 and totalKeysExamined > 0 , this is the case when you have the so called "covered query" , this is the fastest case where you search and load only from the index in memory and do not touch the rest part of the documents from storage.

user_104150470
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