pkuwm commented on a change in pull request #1109:
URL: https://github.com/apache/helix/pull/1109#discussion_r445215378
##########
File path:
zookeeper-api/src/main/java/org/apache/helix/zookeeper/zkclient/ZkClient.java
##########
@@ -984,11 +997,51 @@ private void fireAllEvents() {
protected List<String> getChildren(final String path, final boolean watch) {
long startT = System.currentTimeMillis();
+
try {
List<String> children = retryUntilConnected(new Callable<List<String>>()
{
+ private int connectionLossRetryCount = 0;
+
@Override
public List<String> call() throws Exception {
- return getConnection().getChildren(path, watch);
+ try {
+ return getConnection().getChildren(path, watch);
+ } catch (ConnectionLossException e) {
+ ++connectionLossRetryCount;
+ // Allow retrying 3 times before checking stat checking number of
children,
+ // because there is a higher possibility that connection loss is
caused by other
+ // factors such as network connectivity, connected ZK node could
not serve
+ // the request, session expired, etc.
+ if (connectionLossRetryCount >= 3) {
+ // Issue: https://github.com/apache/helix/issues/962
+ // Connection loss might be caused by an excessive number of
children.
+ // Infinitely retrying connecting may cause high GC in ZK server
and kill ZK server.
+ // This is a workaround to check numChildren to have a chance to
exit retry loop.
+ // TODO: remove this check once we have a better way to exit
infinite retry
+ Stat stat = getStat(path);
+ if (stat != null) {
+ if (stat.getNumChildren() > NUM_CHILDREN_LIMIT) {
+ LOG.error("Failed to get children for path {} because number
of children {} "
+ + "exceeds limit {}, aborting retry.", path,
stat.getNumChildren(),
+ NUM_CHILDREN_LIMIT);
+ // There is not an accurate KeeperException for the purpose.
+ // MarshallingErrorException could represent transport error,
+ // so use it to exit retry loop and tell that zk is not able
to
+ // transport the data because packet length is too large.
+ throw new KeeperException.MarshallingErrorException();
Review comment:
@kaisun2000 Yeah you caught it. I meant there is **no** extra impact.
Sorry for the confusion.
Yes, as I mentioned, there are two options:
1. throw `KeeperException.MarshallingErrorException`. This will be
converted by retryUntilConnected to ZkException. Benefit is we don't change
retryUntilConnected.
2. throw ZkException. Benefit is we could add message in the exception. But
we have to change retryUntilConnected to catch ZkException and rethrow it.
Considering this is a workaround and later we remove the logic, I use
`KeeperException.MarshallingErrorException` here. What do you think?
@kaisun2000
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