jiajunwang commented on a change in pull request #1109:
URL: https://github.com/apache/helix/pull/1109#discussion_r454108196
##########
File path:
zookeeper-api/src/main/java/org/apache/helix/zookeeper/zkclient/ZkClient.java
##########
@@ -984,11 +997,50 @@ 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);
+ // MarshallingErrorException could represent transport
error: exceeding the
+ // Jute buffer size. 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();
+ } else {
+ // No need to do stat again for next connection loss.
+ connectionLossRetryCount = 0;
Review comment:
> Your logic here is only allow retrying 3 times, after 3 retries, exit
retry loop.
Could you please check my logic carefully. It will keep retrying if the
ChildrenCount is good. It is "||", not "&&". It is doing almost the same as
your logic. getChildrenCount() won't be called if the count is smaller than 3.
This is helping you to simplify the code.
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