Avoid making further transport calls if paginationStrategy outputs empty entities

[gargharsh3134]

Description

For paginated _list/indices and _list/shards APIs, if their corresponding strategies don't output any entities, the indicesToBeQueried gets set to empty and any subsequent IndicesStatsTransport action ends up fetching stats for all the indices. Change in this PR addresses and optimizes such scenarios.

Functional Testing:

Added following additional info logs just for the testing purpose (no need to include such logs in main):

protected Table buildTable(
        final RestRequest request,
        final Map<String, Settings> indicesSettings,
        final Map<String, ClusterIndexHealth> indicesHealths,
        final Map<String, IndexStats> indicesStats,
        final Map<String, IndexMetadata> indicesMetadatas,
        final Iterator<Tuple<String, Settings>> tableIterator,
        final PageToken pageToken
    ) {
        final String healthParam = request.param("health");
        final Table table = getTableWithHeader(request, pageToken);

        llogger.info("Building table after querying {} indices stats", indicesStats.size());

        while (tableIterator.hasNext()) {
            final Tuple<String, Settings> tuple = tableIterator.next();
            String indexName = tuple.v1();

// For paginated queries, if strategy outputs no indices to be returned,
 // avoid fetching indices stats.
 if (shouldSkipIndicesStatsRequest(paginationStrategy)) {
     logger.info("Skipping indices stats call");
      groupedListener.onResponse(EMPTY_INDICES_STATS_RESPONSE);
} 

private void sendIndicesStatsRequest(
        final String[] indices,
        final IndicesOptions indicesOptions,
        final boolean includeUnloadedSegments,
        final NodeClient client,
        final ActionListener<IndicesStatsResponse> listener
    ) {
        logger.info("Sending indices stats request");
        final IndicesStatsRequest request = new IndicesStatsRequest();
}

local cluster's indices:

gkharsh@bcd07443f159 OpenSearch % curl "localhost:9200/_list/indices"    
green open index4-test s2AJ5CoYRru-8lbB871pWA 2 3 0 0 1.6kb 416b
green open test-index2 k5FNOQcvSV679Hcs1g-OwQ 2 3 0 0 1.6kb 416b
green open test-index  FclPNwqmQie3RnpoOYpLTg 2 3 0 0 1.6kb 417b
next_token null

Before making changes, querying for a wildcard which doesn't match any index was leading to all the index stats being fetched unnecessarily.

gkharsh@bcd07443f159 OpenSearch % curl "localhost:9200/_list/indices/hi*"
next_token null

[2024-10-23T12:10:15,527][INFO ][o.o.r.a.l.RestIndicesListAction] [master1] Sending indices stats request
[2024-10-23T12:10:15,543][INFO ][o.o.r.a.l.RestIndicesListAction] [master1] Building table after querying 3 indices stats

After making the changes, stats call is not being made:

gkharsh@bcd07443f159 OpenSearch % curl "localhost:9200/_list/indices/hi*"
next_token null

[2024-10-23T12:13:31,506][INFO ][o.o.r.a.l.RestIndicesListAction] [master1] Skipping indices stats call
[2024-10-23T12:13:31,515][INFO ][o.o.r.a.l.RestIndicesListAction] [master1] Building table after querying 0 indices stats

Related Issues

Resolves #16448

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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[github-actions]

✅ Gradle check result for 523acf6: SUCCESS

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 11 lines in your changes missing coverage. Please review.

Project coverage is 72.09%. Comparing base (9489a21) to head (6d0acfc).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
...admin/cluster/shards/TransportCatShardsAction.java	0.00%	5 Missing ⚠️
.../opensearch/rest/action/cat/RestIndicesAction.java	0.00%	5 Missing ⚠️
...tion/admin/indices/stats/IndicesStatsResponse.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #16444      +/-   ##
============================================
+ Coverage     72.04%   72.09%   +0.05%     
- Complexity    65020    65056      +36     
============================================
  Files          5313     5313              
  Lines        303356   303365       +9     
  Branches      43900    43902       +2     
============================================
+ Hits         218551   218718     +167     
+ Misses        66905    66728     -177     
- Partials      17900    17919      +19     

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[github-actions]

❌ Gradle check result for 016fcaf: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[rajiv-kv]

LGTM

[shwetathareja]

@gargharsh3134 can we add test for it?

[github-actions]

❌ Gradle check result for a44870a: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[gargharsh3134]

can we add test for it?

@shwetathareja I did discuss this earlier with @rajiv-kv. But, we don't have any UTs for RestLayer and It won't be possible to assert this info in an Integ Test, that's why I just added functional testing details. It is the behaviour of each TransportNodesAction, that if indices in the request are not set, we end up fetching everything, Not really sure how to have this in tests. Would you have any suggestions?

[github-actions]

❕ Gradle check result for 6d0acfc: UNSTABLE

Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[gargharsh3134]

Opened an issue to track addition of integ tests inside TransportActions -> #16454

[shwetathareja]

Approving it so that it can make it to 2.18. Test will be added as fast follow immediately.