pkuwm commented on a change in pull request #1109:
URL: https://github.com/apache/helix/pull/1109#discussion_r443906147
##########
File path:
zookeeper-api/src/main/java/org/apache/helix/zookeeper/zkclient/ZkClient.java
##########
@@ -103,6 +109,13 @@
// ZkEventThread. Otherwise the retry request might block the normal event
processing.
protected final ZkAsyncRetryThread _asyncCallRetryThread;
+ static {
Review comment:
I don't want to change the original init way for
MAX_RECONNECT_INTERVAL_MS.
Like I comment, in terms of NUM_CHILDREN_LIMIT, the purpose is for unit
test. I explain it in comment: Set it here for unit test to use reflection to
change value because compilers optimize constants by replacing them inline. If
we don't do it like this, we would not be able to unit test getChildren()
unless we create > 100K children.
##########
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:
I considered both. `BadArgumentsException` was the one I tried to use,
but realized that `MarshallingErrorException` could represent a transport error
and mostly mean data exceeds jute.maxbuffer. Here is an example:
https://tgockel.github.io/zookeeper-cpp/classzk_1_1marshalling__error.html#details
`An error occurred while marshalling data. The most common cause of this is
exceeding the Jute buffer size – meaning the transaction was too large`
So I decided to choose MarshallingError. BadArgumentsException for me
sounds more like the API is misused, eg, invalid path that has extra slash
"/path/".
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