[GitHub] [pulsar] michaeljmarshall commented on a diff in pull request #17241: [managed-ledger] Do not send duplicate reads to BK/offloaders

[GitBox <gi...@apache.org>]

michaeljmarshall commented on code in PR #17241:
URL: https://github.com/apache/pulsar/pull/17241#discussion_r966626418


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managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/cache/PendingReadsManager.java:
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@@ -0,0 +1,447 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.bookkeeper.mledger.impl.cache;
+
+import static org.apache.bookkeeper.mledger.impl.ManagedLedgerImpl.createManagedLedgerException;
+import io.prometheus.client.Counter;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicBoolean;
+import lombok.AllArgsConstructor;
+import lombok.Value;
+import org.apache.bookkeeper.client.api.ReadHandle;
+import org.apache.bookkeeper.mledger.AsyncCallbacks;
+import org.apache.bookkeeper.mledger.Entry;
+import org.apache.bookkeeper.mledger.ManagedLedgerException;
+import org.apache.bookkeeper.mledger.impl.EntryImpl;
+
+/**
+ * PendingReadsManager tries to prevent sending duplicate reads to BK.
+ */
+public class PendingReadsManager {
+
+    private static final Counter COUNT_ENTRIES_READ_FROM_BK = Counter
+            .build()
+            .name("pulsar_ml_cache_pendingreads_entries_read")
+            .help("Total number of entries read from BK")
+            .register();
+
+    private static final Counter COUNT_ENTRIES_NOTREAD_FROM_BK = Counter
+            .build()
+            .name("pulsar_ml_cache_pendingreads_entries_notread")
+            .help("Total number of entries not read from BK")
+            .register();
+
+    private static final Counter COUNT_PENDING_READS_MATCHED = Counter
+            .build()
+            .name("pulsar_ml_cache_pendingreads_matched")
+            .help("Pending reads reused with perfect range match")
+            .register();
+    private static final Counter COUNT_PENDING_READS_MATCHED_INCLUDED = Counter
+            .build()
+            .name("pulsar_ml_cache_pendingreads_matched_included")
+            .help("Pending reads reused by attaching to a read with a larger range")
+            .register();
+    private static final Counter COUNT_PENDING_READS_MISSED = Counter
+            .build()
+            .name("pulsar_ml_cache_pendingreads_missed")
+            .help("Pending reads that didn't find a match")
+            .register();
+
+    private static final Counter COUNT_PENDING_READS_MATCHED_OVERLAPPING_MISS_LEFT = Counter
+            .build()
+            .name("pulsar_ml_cache_pendingreads_matched_overlapping_miss_left")
+            .help("Pending reads that didn't find a match but they partially overlap with another read")
+            .register();
+
+    private static final Counter COUNT_PENDING_READS_MATCHED_BUT_OVERLAPPING_MISS_RIGHT = Counter
+            .build()
+            .name("pulsar_ml_cache_pendingreads_matched_overlapping_miss_right")
+            .help("Pending reads that didn't find a match but they partially overlap with another read")
+            .register();
+
+    private static final Counter COUNT_PENDING_READS_MATCHED_BUT_OVERLAPPING_MISS_BOTH = Counter
+            .build()
+            .name("pulsar_ml_cache_pendingreads_matched_overlapping_miss_both")
+            .help("Pending reads that didn't find a match but they partially overlap with another read")
+            .register();

Review Comment:
   I know it is a little late, but I am wondering if there is a reason we created so many metrics here instead of using a single metric with different labels to differentiate certain outcomes. These metrics could probably have been 3 metrics each with 2 or 3 unique labels. For example, `COUNT_PENDING_READS_MATCHED_BUT_OVERLAPPING_MISS_RIGHT` could be `COUNT_PENDING_READS_MATCHED_BUT_OVERLAPPING` with a label indicating that the miss was `right`, `left`, or `both`. In my experience, this makes made Grafana dashboards simpler because you can aggregate the whole metric or break it out by label. I am not aware of any performance implications.
   
   Here is the prometheus guide to metric and label names that supports using labels to differentiate a single metric: https://prometheus.io/docs/practices/naming/#labels.



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