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mongo/src/mongo/db/query/README.md at master · mongodb/mongo

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Disclaimer: This is a work in progress. It is not complete and we will do our best to complete it in a timely manner. The query system generally is responsible for interpreting the user's request, finding an optimal way to satisfy it, and to actually compute the results. It is primarily exposed through the find and aggregate commands, but also used in associated read commands like count, distinct, and mapReduce. Here we will divide it into the following phases and topics: In this documentation we focus on the process for a single node or replica set where all the data is expected to be found locally. We plan to add documentation for the sharded case in the src/mongo/s/query/ directory later. The following commands are generally maintained by the query team, with the majority of our focus given to the first two. The code path for each of these starts in a Command, named something like MapReduceCommand or FindCmd. You can generally find these in src/mongo/db/commands/. The first round of

Query System Internals Overview The query system is responsible for interpreting the user's request, finding an optimal way to satisfy it, and computing the final results. It is primarily exposed through the find and aggregate commands, but also used in associated read commands such as count, distinct, and mapReduce and write commands such as update, delete, and findAndModify. Query Optimization Architecture Guide The QO Architecture Guide provides an overview of the query system components maintained by the QO team, including parsing, heuristic rewrites, query planning, plan caching,…

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