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https://issues.apache.org/jira/browse/IGNITE-9026?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16948448#comment-16948448
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Maxim Muzafarov commented on IGNITE-9026:
-----------------------------------------
Moved to the next release due to inactivity. Please, feel free to move it back
if you will be able to complete the ticket by 2.8 code freeze date, December 2,
2019.
> Two levels of Peer class loading fails in CONTINUOUS mode
> ---------------------------------------------------------
>
> Key: IGNITE-9026
> URL: https://issues.apache.org/jira/browse/IGNITE-9026
> Project: Ignite
> Issue Type: Bug
> Affects Versions: 2.5
> Reporter: David Harvey
> Assignee: David Harvey
> Priority: Major
> Fix For: 2.8
>
> Attachments: master_1b3742f4d7_p2p_two_hops.patch
>
>
> We had an seemingly functional system in SHARED_MODE, where we have a custom
> StreamReceiver that sometimes sends closures on the peer class loaded code to
> other servers. However, we ended up running out of Metaspace, because we had
> > 6000 class loaders! We suspected a regression in this change
> [https://github.com/apache/ignite/commit/d2050237ee2b760d1c9cbc906b281790fd0976b4#diff-3fae20691c16a617d0c6158b0f61df3c],
> so we switched to CONTINUOUS mode. We then started getting failures to
> load some of the classes for the closures on the second server. Through
> some testing and code inspection, there seems to be the following flaws
> between GridDeploymentCommunication.sendResourceRequest and its two callers.
> The callers iterate though all the participant nodes until they find an
> online node that responds to the request (timeout is treated as offline
> node), with either success or failure, and then the loop terminates. The
> assumption is that all nodes are equally capable of providing the resource,
> so if one fails, then the others would also fail.
> The first flaw is that GridDeploymentCommunication.sendResourceRequest() has
> a check for a cycle, i.e., whether the destination node is one of the nodes
> that originated or forwarded this request, and in that case, a failure
> response is faked. However, that causes the caller's loop to terminate. So
> depending on the order of the nodes in the participant list,
> sendResourceRequest() may fail before trying any nodes because it has one of
> the calling nodes on this list. It should instead be skipping any of the
> calling nodes.
> Example with 1 client node a 2 server nodes: C1 sends data to S1, which
> forwards closure to S2. C1 also sends to S2 which forwards to S1. So now
> the node lists on S1 and S2 contain C1 and the other S node. If the order
> of the node lists on S1 is (S2,C1) and on S2 (S1,C1), then when S1 tries to
> load a class, it will try S2, then S2 will try S1, but will get a fake
> failure generated, causing S2 not to try more nodes (i.e., C1), and causing
> S1 also not to try more nodes.
> The other flaw is the assumption that all participants have equal access to
> the resource. Assume S1 knows about userVersion1 via S3 and S4, with S3
> though C1 and S4 through C2. If C2 fails, then S4 is not capable of getting
> back to a master, but S1 has no way of knowing that.
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