adixitconfluent commented on code in PR #17539:
URL: https://github.com/apache/kafka/pull/17539#discussion_r1816851362


##########
core/src/main/java/kafka/server/share/DelayedShareFetch.java:
##########
@@ -204,7 +211,154 @@ Map<TopicIdPartition, FetchRequest.PartitionData> 
acquirablePartitions() {
         return topicPartitionData;
     }
 
-    private void releasePartitionLocks(String groupId, Set<TopicIdPartition> 
topicIdPartitions) {
+    // In case, fetch offset metadata doesn't exist for any topic partition in 
the list of topic partitions, we do a
+    // replicaManager.readFromLog to populate the offset metadata.
+    private MaybeUpdateFetchOffsetMetadataResult 
maybeUpdateFetchOffsetMetadataForTopicPartitions(Map<TopicIdPartition, 
FetchRequest.PartitionData> topicPartitionData) {
+        boolean isFetchOffsetMetadataUpdated = false;
+        Map<TopicIdPartition, FetchRequest.PartitionData> 
missingFetchOffsetMetadataTopicPartitions = new LinkedHashMap<>();
+        Map<TopicIdPartition, FetchPartitionOffsetData> 
replicaManagerReadResponseData;
+        for (Map.Entry<TopicIdPartition, FetchRequest.PartitionData> entry : 
topicPartitionData.entrySet()) {
+            TopicIdPartition topicIdPartition = entry.getKey();
+            SharePartition sharePartition = 
sharePartitionManager.sharePartition(shareFetchData.groupId(), 
topicIdPartition);
+            if (sharePartition == null) {
+                log.debug("Encountered null share partition for groupId={}, 
topicIdPartition={}. Skipping it.", shareFetchData.groupId(), topicIdPartition);
+                continue;
+            }
+            if (sharePartition.latestFetchOffsetMetadata().isEmpty())
+                
missingFetchOffsetMetadataTopicPartitions.put(topicIdPartition, 
entry.getValue());
+        }
+
+        if (missingFetchOffsetMetadataTopicPartitions.isEmpty()) {
+            return new MaybeUpdateFetchOffsetMetadataResult(false, null);
+        }
+        // We fetch data from replica manager corresponding to the topic 
partitions that have missing fetch offset metadata.
+        replicaManagerReadResponseData = 
readFromLog(missingFetchOffsetMetadataTopicPartitions);
+
+        for (Map.Entry<TopicIdPartition, FetchRequest.PartitionData> entry : 
missingFetchOffsetMetadataTopicPartitions.entrySet()) {
+            TopicIdPartition topicIdPartition = entry.getKey();
+            SharePartition sharePartition = 
sharePartitionManager.sharePartition(shareFetchData.groupId(), 
topicIdPartition);
+            if (sharePartition == null) {
+                log.debug("Encountered null share partition for groupId={}, 
topicIdPartition={}. Skipping it.", shareFetchData.groupId(), topicIdPartition);
+                continue;
+            }
+            FetchPartitionOffsetData fetchPartitionOffsetData = 
replicaManagerReadResponseData.get(topicIdPartition);
+            if (fetchPartitionOffsetData == null) {
+                log.debug("Replica manager read log result {} does not contain 
topic partition {}",
+                    replicaManagerReadResponseData, topicIdPartition);
+                continue;
+            }
+            
sharePartition.updateLatestFetchOffsetMetadata(fetchPartitionOffsetData.logOffsetMetadata());
+            isFetchOffsetMetadataUpdated = true;
+        }
+        return new 
MaybeUpdateFetchOffsetMetadataResult(isFetchOffsetMetadataUpdated, 
replicaManagerReadResponseData);
+    }
+
+    private boolean isMinBytesSatisfied(Map<TopicIdPartition, 
FetchRequest.PartitionData> topicPartitionData) {
+        long accumulatedSize = 0;
+        try {
+            for (Map.Entry<TopicIdPartition, FetchRequest.PartitionData> entry 
: topicPartitionData.entrySet()) {
+                TopicIdPartition topicIdPartition = entry.getKey();
+                FetchRequest.PartitionData partitionData = entry.getValue();
+                Partition partition = 
replicaManager.getPartitionOrException(topicIdPartition.topicPartition());
+                LogOffsetSnapshot offsetSnapshot = 
partition.fetchOffsetSnapshot(Optional.empty(), true);
+                // The FetchIsolation type that we use for share fetch is 
FetchIsolation.HIGH_WATERMARK. In the future, we can
+                // extend it other FetchIsolation types.
+                FetchIsolation isolationType = 
shareFetchData.fetchParams().isolation;
+                LogOffsetMetadata endOffsetMetadata;
+                if (isolationType == FetchIsolation.LOG_END)
+                    endOffsetMetadata = offsetSnapshot.logEndOffset;
+                else if (isolationType == FetchIsolation.HIGH_WATERMARK)
+                    endOffsetMetadata = offsetSnapshot.highWatermark;
+                else
+                    endOffsetMetadata = offsetSnapshot.lastStableOffset;
+
+                if (endOffsetMetadata == 
LogOffsetMetadata.UNKNOWN_OFFSET_METADATA)
+                    continue;
+
+                SharePartition sharePartition = 
sharePartitionManager.sharePartition(shareFetchData.groupId(), 
topicIdPartition);
+                if (sharePartition == null) {
+                    return true;
+                }
+
+                Optional<LogOffsetMetadata> optionalFetchOffsetMetadata = 
sharePartition.latestFetchOffsetMetadata();
+                if (optionalFetchOffsetMetadata.isEmpty() || 
optionalFetchOffsetMetadata.get() == LogOffsetMetadata.UNKNOWN_OFFSET_METADATA)
+                    continue;
+                LogOffsetMetadata fetchOffsetMetadata = 
optionalFetchOffsetMetadata.get();
+
+                if (fetchOffsetMetadata.messageOffset > 
endOffsetMetadata.messageOffset) {
+                    log.debug("Satisfying delayed share fetch request for 
group {}, member {} since it is fetching later segments of " +
+                        "topicIdPartition {}", shareFetchData.groupId(), 
shareFetchData.memberId(), topicIdPartition);
+                    return true;

Review Comment:
   It might not be true ever in case we are using 
`FetchIsolation.HIGH_WATERMARK`, but I think it can be true in case we use 
`FetchIsolation.LOG_END` and `FetchIsolation.TXN_COMMITTED` which might be used 
in the future in share fetch requests.



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