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Briefly, this error occurs when the iteration order of bucketOrds, which are used in aggregations in OpenSearch, is altered without any mutation. This could be due to a bug in the code or an unexpected change in the data. To resolve this issue, you can try the following: 1) Review your code to ensure that bucketOrds are being handled correctly. 2) Check your data for any unexpected changes or inconsistencies. 3) Update to the latest version of OpenSearch, as this may contain a fix for the issue. 4) If the problem persists, consider reporting it as a bug to the OpenSearch community.
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This guide will help you check for common problems that cause the log ” Iteration order of [” + bucketOrds + “] changed without mutating. [ ” to appear. To understand the issues related to this log, read the explanation below about the following OpenSearch concepts: aggregations, search.
Quick links
Overview
Search refers to the searching of documents in an index or multiple indices. The simple search is just a GET API request to the _search endpoint. The search query can either be provided in query string or through a request body.
Examples
When looking for any documents in this index, if search parameters are not provided, every document is a hit and by default 10 hits will be returned.
GET my_documents/_search
A JSON object is returned in response to a search query. A 200 response code means the request was completed successfully.
{
"took" : 1,
"timed_out" : false,
"_shards" : {
"total" : 2,
"successful" : 2,
"failed" : 0
},
"hits" : {
"total" : 2,
"max_score" : 1.0,
"hits" : [
...
]
}
}Notes and good things to know
- Distributed search is challenging and every shard of the index needs to be searched for hits, and then those hits are combined into a single sorted list as a final result.
- There are two phases of search: the query phase and the fetch phase.
- In the query phase, the query is executed on each shard locally and top hits are returned to the coordinating node. The coordinating node merges the results and creates a global sorted list.
- In the fetch phase, the coordinating node brings the actual documents for those hit IDs and returns them to the requesting client.
- A coordinating node needs enough memory and CPU in order to handle the fetch phase.
Log Context
Log “Iteration order of [” + bucketOrds + “] changed without mutating. [” class name is BucketsAggregator.java. We extracted the following from OpenSearch source code for those seeking an in-depth context :
for (int ordIdx = 0; ordIdx < owningBucketOrds.length; ordIdx++) {
List buckets = new ArrayList<>((int) bucketOrds.size());
LongKeyedBucketOrds.BucketOrdsEnum ordsEnum = bucketOrds.ordsEnum(owningBucketOrds[ordIdx]);
while(ordsEnum.next()) {
if (bucketOrdsToCollect[b] != ordsEnum.ord()) {
throw new AggregationExecutionException("Iteration order of [" + bucketOrds + "] changed without mutating. ["
+ ordsEnum.ord() + "] should have been [" + bucketOrdsToCollect[b] + "]");
}
buckets.add(bucketBuilder.build(ordsEnum.value(); bucketDocCount(ordsEnum.ord()); subAggregationResults[b++]));
}
results[ordIdx] = resultBuilder.build(owningBucketOrds[ordIdx]; buckets);
