How to collect docs in order in collect() method of a custom aggregator

Elastic Stack Elasticsearch
1

I am developing a custom aggregator using ES 1.3.4. It extends from
NumericMetricsAggregator.MultiValue class. Its code structure closely
resembles that of the Stats aggregator. For my requirements, I need the doc
Ids to be received in ascending order in the overridden collect() method.
For most queries, I do get the doc Ids in ascending order. Interestingly
for bool should queries with multiple clauses, I get doc Ids in descending
order. How can I fix this? Is this a bug?

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2

I asked the same question on github and got the answer which worked for me.
Here's the solution:

You can call aggregationContext.ensureScoreDocsInOrder(); to make sure that
docs are going to come in order, have a look for instance at
ReverseNestedAggregator which uses this method.

Queries are indeed allowed to emit documents out-of-order if allowed to do
so and if it makes things faster. I believe the only case when it happens
today is when you get Lucene's BooleanScorer which is used for top-level
disjunctions, so your observation makes sense.

Link to the issue:

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