pkuwm commented on a change in pull request #1109:
URL: https://github.com/apache/helix/pull/1109#discussion_r449386378
##########
File path:
zookeeper-api/src/main/java/org/apache/helix/zookeeper/zkclient/ZkClient.java
##########
@@ -1503,12 +1555,14 @@ private void acquireEventLock() {
} catch (Exception e) {
throw ExceptionUtil.convertToRuntimeException(e);
}
+
// before attempting a retry, check whether retry timeout has elapsed
if (System.currentTimeMillis() - operationStartTime >
_operationRetryTimeoutInMillis) {
throw new ZkTimeoutException("Operation cannot be retried because of
retry timeout ("
+ _operationRetryTimeoutInMillis + " milli seconds). Retry was
caused by "
+ retryCauseCode);
}
+ LOG.warn("Retrying operation, caused by {}", retryCauseCode);
Review comment:
From the debugging experience, it seems this is helpful log indicating
retryable error like connection loss or session expired. Otherwise, it keeps
retrying silently. Considering flooded logs, maybe we could have a backoff
strategy or very N retry times to log it? Just a thought.
I will not add it for now.
##########
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:
@jiajunwang I would like to check numChildren every 3 connection loss,
because:
allow trying 3 times before checking numChildren, because there is higher
possibility connection loss is caused by session expired, etc. I don't want it
to check numChildren for each connection loss which will downgrade the
performance.
Your logic here is only allow retrying 3 times, after 3 retries, exit retry
loop. This is not what I want. I would still keep the original logic to retry
on retry-able connection loss.
##########
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 {} "
Review comment:
Done.
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