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Mongo count operation called twice in QuerydslMongoPredicateExecutor.findAll(Predicate, Pageable) [DATAMONGO-1860] #2761

spring-projects-issues opened this issue Jan 26, 2018 · 1 comment


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@spring-projects-issues spring-projects-issues commented Jan 26, 2018

Erik T opened DATAMONGO-1860 and commented

return PageableExecutionUtils.getPage(applyPagination(query, pageable).fetchResults().getResults(), pageable,
() -> createQueryFor(predicate).fetchCount());

Count is a very expensive operation in MongoDB

In snippet above, fetchResults() internally calls count to populate total count of QueryResults.
Again, fetchCount also calls count.

final QueryResults<T> queryResults = applyPagination(query, pageable).fetchResults();
return PageableExecutionUtils.getPage(queryResults.getResults(), pageable,
() -> queryResults.getTotal());

would end up calling count once.

Moreover, giving the option of returning Slice<T> as well as Page<T>, and do away with count altogether would also be a nice addition.

Affects: 2.0.3 (Kay SR3)

Reference URL:

Referenced from: pull request #529

Backported to: 2.0.4 (Kay SR4), 1.10.11 (Ingalls SR11)

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@spring-projects-issues spring-projects-issues commented Jan 28, 2018

Mark Paluch commented

Hey Erik T, thanks for raising this issue. Reusing the count from QueryResults makes sense. Going forward with this topic we could use fetch() instead and retrieve the count only if necessary

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