Reduce memory overhead of searches

hapi-fhir-docs/src/main/resources/ca/uhn/hapi/fhir/changelog/7_8_0/6469-reduce-memory-overhead-for-searches.yaml

@@ -0,0 +1,8 @@
+---
+type: perf
+issue: 6469
+title: "Searching for a large number of resources can use a lot of
+        memory, due to the nature of deduplication of results in memory.
+        We will instead push this responsibility to the db to save
+        reduce this overhead.
+"

hapi-fhir-jpaserver-base/src/main/java/ca/uhn/fhir/jpa/search/SearchCoordinatorSvcImpl.java

@@ -66,6 +66,7 @@
 import com.google.common.annotations.VisibleForTesting;
 import jakarta.annotation.Nonnull;
 import jakarta.annotation.Nullable;
+import org.apache.commons.lang3.ObjectUtils;
 import org.apache.commons.lang3.time.DateUtils;
 import org.hl7.fhir.instance.model.api.IBaseResource;
 import org.springframework.beans.factory.BeanFactory;
@@ -376,6 +377,7 @@ public IBundleProvider registerSearch(
 				myContext.getResourceDefinition(theResourceType).getImplementingClass();
 		final ISearchBuilder<JpaPid> sb = mySearchBuilderFactory.newSearchBuilder(theResourceType, resourceTypeClass);
 		sb.setFetchSize(mySyncSize);
+		sb.setRequireTotal(theParams.getCount() != null);
 
 		final Integer loadSynchronousUpTo = getLoadSynchronousUpToOrNull(theCacheControlDirective);
 		boolean isOffsetQuery = theParams.isOffsetQuery();
@@ -393,14 +395,23 @@ public IBundleProvider registerSearch(
 
 				try {
 					return direct.get();
-
 				} catch (ResourceNotFoundInIndexException theE) {
 					// some resources were not found in index, so we will inform this and resort to JPA search
 					ourLog.warn(
 							"Some resources were not found in index. Make sure all resources were indexed. Resorting to database search.");
 				}
 			}
 
+			// we set a max to fetch from the db for synchronous searches;
+			// otherwise, we would have to load everything into memory (or force the db to do so);
+			// So let's set a max value here
+			Integer maxToLoad = ObjectUtils.firstNonNull(
+					loadSynchronousUpTo,
+					theParams.getCount() != null ? theParams.getCount() + 1 : null,
+					myStorageSettings.getInternalSynchronousSearchSize());
+			ourLog.debug("Setting a max fetch value of {} for synchronous search", maxToLoad);
+			sb.setMaxResultsToFetch(maxToLoad);
+
 			ourLog.debug("Search {} is loading in synchronous mode", searchUuid);
 			return mySynchronousSearchSvc.executeQuery(
 					theParams, theRequestDetails, searchUuid, sb, loadSynchronousUpTo, theRequestPartitionId);

hapi-fhir-jpaserver-base/src/main/java/ca/uhn/fhir/jpa/search/SynchronousSearchSvcImpl.java

@@ -249,7 +249,7 @@ public IBundleProvider executeQuery(
 							resources, theRequestDetails, myInterceptorBroadcaster);
 
 					SimpleBundleProvider bundleProvider = new SimpleBundleProvider(resources);
-					if (hasACount) {
+					if (hasACount && theSb.requiresTotal()) {
 						bundleProvider.setTotalResourcesRequestedReturned(receivedResourceCount);
 					}
 					if (theParams.isOffsetQuery()) {