I use mongo's explain() to check the performance of some queries, sometimes a keep_mutation stage will show up like the following:
"executionStats" : {
...
"executionStages" : {
"stage" : "KEEP_MUTATIONS",
"nReturned" : 1,
"executionTimeMillisEstimate" : 5460,
"works" : 79622,
...
}
}
I want to know more about this stage so I search through the internet, and to my surprise, I couldn't find useful info related to it even in the official document, let alone other websites. Could someone help to explain that?