guluo2016 commented on code in PR #6439:
URL: https://github.com/apache/hbase/pull/6439#discussion_r1835355418
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hbase-server/src/main/java/org/apache/hadoop/hbase/mob/RSMobFileCleanerChore.java:
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@@ -116,14 +120,32 @@ protected void chore() {
Set<String> regionMobs = new HashSet<String>();
Path currentPath = null;
try {
- // collectinng referenced MOBs
+ // collecting referenced MOBs
for (HStoreFile sf : sfs) {
currentPath = sf.getPath();
- sf.initReader();
- byte[] mobRefData =
sf.getMetadataValue(HStoreFile.MOB_FILE_REFS);
- byte[] bulkloadMarkerData =
sf.getMetadataValue(HStoreFile.BULKLOAD_TASK_KEY);
- // close store file to avoid memory leaks
- sf.closeStoreFile(true);
+ byte[] mobRefData = null;
+ byte[] bulkloadMarkerData = null;
+ boolean needCreateReader = false;
+ if (sf.getReader() == null) {
+ synchronized (sf) {
+ if (sf.getReader() == null) {
+ needCreateReader = true;
+ sf.initReader();
+ mobRefData =
sf.getMetadataValue(HStoreFile.MOB_FILE_REFS);
+ bulkloadMarkerData =
sf.getMetadataValue(HStoreFile.BULKLOAD_TASK_KEY);
+ // close store file to avoid memory leaks
+ sf.closeStoreFile(true);
+ }
+ }
+ }
+ // If the StoreFileReader object was created by another
thread, even if the reader
+ // has been closed now, we can still obtain the data by
HStoreFile.metataMap,
+ // because the map will not be cleared when the reader is
closed.
+ if (!needCreateReader) {
+ mobRefData = sf.getMetadataValue(HStoreFile.MOB_FILE_REFS);
+ bulkloadMarkerData =
sf.getMetadataValue(HStoreFile.BULKLOAD_TASK_KEY);
+ }
Review Comment:
Indeed, writing code this way will be much more concise.
But at the same time, I think performance also needs to be considered.
When the reader does not need to be created by itself, We do not need to
perform read operations in the synchronization code block because locking may
cause other threads to wait. In this case, exiting the synchronization code
block early may reduce the waiting time for other threads. （If there are other
threads waiting to obtain this lock）
Therefore, when executing the following code, I think it needs to be divided
into two cases:
```java
if (sf.getReader() == null) {
synchronized (sf) {
boolean needCreateReader = sf.getReader() == null;
// Case 1: needCreateReader = true, create reader, and do something
// Case 2: needCreateReader = false, exit the synchronization code
block to reduce performance overhead
}
}
```
What do you think?
I look forward to your response. Thanks a lot!
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