mongodb, sort skip limit, pipeline -- Выясняем как тут сортировать данные при агрегации

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vedro-compota's picture
Submitted by vedro-compota on Mon, 01/22/2018 - 16:35

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$sort + $limit Memory Optimization

When a sort immediately precedes a limit in the pipeline, the $sort operation only maintains the top n results as it progresses, where n is the specified limit, and MongoDB only needs to store n items in memory. This optimization still applies when allowDiskUse is true and the n items exceed the aggregation memory limit.

Changed in version 2.4: Before MongoDB 2.4, $sort would sort all the results in memory, and then limit the results to n results.

Optimizations are subject to change between releases.

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vedro-compota's picture

vedro-compota

Mon, 01/22/2018 - 17:50

проблема наблюдалась в 3.2 в 3.6 всё норм

то есть не работал запрос вида:

db.federal_subject.aggregate([
	{"$sort":{"_id":1,}},
	{"$skip":10},
	{"$limit":5}
],
{"allowDiskUse":true,"cursor":{"batchSize":1000}}
)

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