commit a7f2a2eceaaeb4e101c6fd51a6868b48c8d1214f
author Andrey Yegorov <8622884+dlg99@users.noreply.github.com> Mon Feb 01 01:54:43 2021 -0800
committer GitHub <noreply@github.com> Mon Feb 01 10:54:43 2021 +0100
tree 6e23a025fdc6cefa10de5cabcc8c46b56489cf26
parent c5e4c8645bb08c4b0ba65d15c8b4d0084bd09c68

Limit log output to prevent in case of the large group of the log segments

Descriptions of the changes in this PR:

Limit logged data

### Motivation

Overly long log line at ReadAheadEntryReader
Found a log with single log line of over 5 mil characters long
"org.apache.distributedlog.ReadAheadEntryReader - Starting the readahead entry reader for ..." + the details of ~16000 segments.

### Changes

Output details of up to 10 segments plus count of segments.

Master Issue: #2561



Reviewers: Enrico Olivelli <eolivelli@gmail.com>, Nicolo Boschi <boschi1997@gmail.com>

This closes #2562 from dlg99/master-log

stream/distributedlog/core/src/main/java/org/apache/distributedlog/ReadAheadEntryReader.java

diff --git a/stream/distributedlog/core/src/main/java/org/apache/distributedlog/ReadAheadEntryReader.java b/stream/distributedlog/core/src/main/java/org/apache/distributedlog/ReadAheadEntryReader.java
index 11a7e7e..915d81a 100644
--- a/stream/distributedlog/core/src/main/java/org/apache/distributedlog/ReadAheadEntryReader.java
+++ b/stream/distributedlog/core/src/main/java/org/apache/distributedlog/ReadAheadEntryReader.java
@@ -33,6 +33,8 @@
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Function;
+import java.util.stream.Collectors;
+
 import org.apache.bookkeeper.common.concurrent.FutureEventListener;
 import org.apache.bookkeeper.common.concurrent.FutureUtils;
 import org.apache.bookkeeper.common.util.OrderedScheduler;
@@ -411,8 +413,12 @@
     }
 
     public void start(final List<LogSegmentMetadata> segmentList) {
-        logger.info("Starting the readahead entry reader for {} : segments = {}",
-                readHandler.getFullyQualifiedName(), segmentList);
+        // Managed to get 5mil character long log line from here.
+        // Will limit the output.
+        logger.info("Starting the readahead entry reader for {} : number of segments: {}, top 10 segments = {}",
+                readHandler.getFullyQualifiedName(), segmentList.size(),
+                segmentList.size() > 10
+                        ? segmentList.stream().limit(10).collect(Collectors.toList()) : segmentList);
         started.set(true);
         processLogSegments(segmentList);
     }