birthdate searching not working for Patient

[Sameer2810]

https://test.com/api/ImagingStudy?_include=ImagingStudy:subject&_include=ImagingStudy:referrer&_total=accurate&_sort=-_lastUpdated&_elements=id,identifier,subject,name,gender,birthDate,modality,description,status,started,numberOfInstances,reasonReference,referrer,extension,location,resultsInterpreter&_count=10&subject:Patient.birthdate=1969-09-14

I have published latest 4.0.728 release version fhir api.
Tried to perform above operation but birthDatesearch not working it is giving below error

Earlier it is working now giving below error

{
"resourceType": "OperationOutcome",
"id": "eabf175d-e2e7-4523-bc6b-aead26133319",
"meta": {
"lastUpdated": "2026-05-01T14:14:59.6079153+00:00"
},
"issue": [
{
"severity": "error",
"code": "throttled",
"diagnostics": "The request rate has exceeded the maximum API request rate and is being throttled. Please try again later."
}
]
}

{
"resourceType": "OperationOutcome",
"id": "79efdb6a-ac6d-4c16-a4bb-8b99eab19ddb",
"meta": {
"lastUpdated": "2026-05-02T07:24:41.8957183+00:00"
},
"issue": [
{
"severity": "error",
"code": "too-costly",
"diagnostics": "The operation was stopped due to the underlying request being too resource intensive. If possible, try narrowing or changing the criteria."
}
]
}

[evachen96]

Hi @Sameer2810, thanks for reaching out! The error seems that you are getting throttled, are you using an aggregator or middleware in front of FHIR server? Also curious to see why you are filtering by so many elements in the query, what is your use case?

[Sameer2810]

Hi @evachen96, I am not using any aggregator or middleware in front of FHIR server. For UI to show study with patient name and physician name that is why filtering these elements in query.

[brendankowitz]

I think these errors indicate that the Cosmos database would benefit from more RUs.

The first error is when Cosmos is consistency throwing 429s, the second error is when the sub-query in a chained search times out:

fhir-server/src/Microsoft.Health.Fhir.CosmosDb/Features/Search/FhirCosmosSearchService.cs

Line 323 in 6faa795

throw new RequestTooCostlyException(Microsoft.Health.Fhir.Core.Resources.ConditionalRequestTooCostly);

[Sameer2810]

Hi @brendankowitz,

Earlier, we were using version 4.0.561 of the FHIR API, and the chained search functionality was working as expected. However, after upgrading to version 4.0.728, we started encountering the above-mentioned error.

Could you please confirm whether this issue is related to the newer version, or if there is any additional configuration or change that we may be missing?

Additionally, we attempted an alternative approach by first querying the Patient resource using the patient’s birthdate and then using the returned Patient IDs to query the ImagingStudy resource. However, even the following query on the Patient resource itself is timing out:

https://test.com/api/Patient?birthdate=1975-08-23&_elements=id&_count=10

Given this behavior, could there be an issue related to indexing/re-indexing of the Patient.birthdate field? Would performing a re-indexing operation help resolve this timeout issue?

Please let us know your thoughts.

[evachen96]

@Sameer2810 We haven't changed anything with the CosmosDB provider in the time between those versions that would make the search more complex. Have you tried with more RUs based on Brendan's message above?

[Sameer2810]

@evachen96 Yes I have tried with more RUs still same issue, earlier RUs were 8000 now I have increased it to 15000 but still same issue

[evachen96]

@Sameer2810 - a few questions: are you able to look into RU utilization in Portal, how many partitions do you have and have the number of partitions increased recently, have you had an increase in data size recently?