Describe the bug

After refactoring aggregation precomputations to a unified API, there are now (almost) consecutive calls to tryPrecomputeAggregationForLeaf and getLeafCollector.

When running aggregations with GlobalOrdinalsStringTermsAggregator, this calls valuesSource.globalOrdinalsValues(ctx); twice, which we've seen to be expensive on several clusters.

My question is: can this value be reused across aggregation computations? As far as I can tell, it's not modified between the two calls, but if it's dangerous to do so would it make sense to at least move

SortedSetDocValues globalOrds = valuesSource.globalOrdinalsValues(ctx);

inside the block:

if (collectionStrategy instanceof DenseGlobalOrds
            && this.resultStrategy instanceof StandardTermsResults
            && subAggregators.length == 0)

to minimize recomputations?

Related component

Search:Aggregations

To Reproduce

Execute a an aggregations query that uses GlobalOrdinalsStringTermsAggregator with expensive globalOrdinalsValues computation.

Expected behavior

Ideally only compute globalOrdinalsValues when it's used and at most once.

Additional Details

Screenshots

Host/Environment (please complete the following information):

• OS: Linux
• Version: 2.19.1