virajjasani commented on a change in pull request #3148:
URL: https://github.com/apache/hadoop/pull/3148#discussion_r659596959
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File path:
hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/DataNode.java
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@@ -2272,19 +2274,11 @@ public int getActiveTransferThreadCount() {
void incrDatanodeNetworkErrors(String host) {
metrics.incrDatanodeNetworkErrors();
- /*
- * Synchronizing on the whole cache is a big hammer, but since it's only
- * accumulating errors, it should be ok. If this is ever expanded to
include
- * non-error stats, then finer-grained concurrency should be applied.
- */
- synchronized (datanodeNetworkCounts) {
- try {
- final Map<String, Long> curCount = datanodeNetworkCounts.get(host);
- curCount.put("networkErrors", curCount.get("networkErrors") + 1L);
- datanodeNetworkCounts.put(host, curCount);
- } catch (ExecutionException e) {
- LOG.warn("failed to increment network error counts for host: {}",
host);
- }
+ try {
+ datanodeNetworkCounts.get(host).compute(NETWORK_ERRORS,
+ (key, errors) -> errors == null ? null : errors + 1L);
Review comment:
So everytime we have a network error, instead of locking entire
LoadingCache, with CHM.compute(), we will just take lock on bucket of Map where
the key resides and then error count will be incremented. So this is fine
grained locking and much performant than taking lock on entire `LoadingCache`.
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