[BUG] _cat/nodes "segments.memory": "0b"

[artemus717]

Describe the bug

_cat/nodes?h=name,heap,memory,Cache&format=json

[
{
"name": "node-hot-04",
"heap.current": "37.8gb",
"heap.percent": "59",
"heap.max": "64gb",
"fielddata.memory_size": "513.8mb",
"query_cache.memory_size": "110.6mb",
"request_cache.memory_size": "643.7mb",
"segments.memory": "0b",
"segments.index_writer_memory": "326.5mb",
"segments.version_map_memory": "11mb",
"segments.fixed_bitset_memory": "1.2kb",
"query_cache.evictions": "581379",
"query_cache.hit_count": "1809845",
"query_cache.miss_count": "60305497",
"request_cache.evictions": "386218",
"request_cache.hit_count": "829303",
"request_cache.miss_count": "1061657",
"script.cache_evictions": "584",
"script.compilation_limit_triggered": "0"
}

"segments.memory": "0b"

No idea, if segments.memory is designed to display 0b or this is a bug.

Related component

Other

To Reproduce

_cat/nodes?h=name,heap,memory,Cache&format=json

Expected behavior

segments.memory response true segments memory statistic.

Additional Details

OpenSearch 2.14.0

[peternied]

[Triage - attendees 1 2 3 4 5 6
@artemus717 Thanks for creating this issue, we'd welcome a pull request to address this issue.

[msfroh]

No idea, if segments.memory is designed to display 0b or this is a bug.

If I recall correctly, Lucene stopped tracking heap usage for segment-level data structures, mostly because it's very close to 0 these days (as everything is memory-mapped and off-heap).

We stopped populating the stat in OpenSearch 2.0 (the first version to use Lucene 9), but continue to include it in node stats for backward compatibility: #2029

[msfroh]

I'm going to close this as "not a bug", but rather a known, intentional change.

Please feel free to comment/reopen if you disagree!