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https://issues.apache.org/jira/browse/TINKERPOP-2569?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17418877#comment-17418877
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ASF GitHub Bot commented on TINKERPOP-2569:
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xiazcy opened a new pull request #1478:
URL: https://github.com/apache/tinkerpop/pull/1478
https://issues.apache.org/jira/browse/TINKERPOP-2569
The issue is that the client's `initialized` field is set to `true` as long
as hosts added, even though the hosts may be dead and the connection pools
failed to initialize, and `submitAsync()` will only re-init() the client (along
with connection pools) if `initialized` is set to false. So even if the server
comes back up, the client will not try to reconnect.
Original approach is to confirm host availability and throw exceptions
during client `init()` when hosts are dead, so that the client's
`initialization` is not set to true, however, this would fail tests that rely
on the "lazy connection" concept (i.e. hosts would need to be available at the
time driver connects). To avoid that, this is a simpler fix that adds a boolean
flag `noLiveHostAvailable` to indicate when there is no live host at client
initialization, so we can re-init() the client in the case it is `true` (in
addition to checking the client `initialized` flag).
This `noLiveHostAvailable` flag is set to `true` initially and is changed
to `false` when any host initiates a connection pool successfully.
Builds successfully with `mvn clean install && mvn verify -pl
gremlin-server,gremlin-console -DskipIntegrationTests=false`.
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> Reconnect to server if Java driver fails to initialize
> ------------------------------------------------------
>
> Key: TINKERPOP-2569
> URL: https://issues.apache.org/jira/browse/TINKERPOP-2569
> Project: TinkerPop
> Issue Type: Bug
> Components: driver
> Affects Versions: 3.4.11
> Reporter: Stephen Mallette
> Priority: Minor
>
> As reported here on SO:
> https://stackoverflow.com/questions/67586427/how-to-recover-with-a-retry-from-gremlin-nohostavailableexception
> If the host is unavailable at {{Client}} initialization then the host is not
> put in a state where reconnect is possible. Essentially, this test for
> {{GremlinServerIntegrateTest}} should pass:
> {code}
> @Test
> public void shouldFailOnInitiallyDeadHost() throws Exception {
> // start test with no server
> this.stopServer();
> final Cluster cluster = TestClientFactory.build().create();
> final Client client = cluster.connect();
> try {
> // try to re-issue a request now that the server is down
> client.submit("g").all().get(3000, TimeUnit.MILLISECONDS);
> fail("Should throw an exception.");
> } catch (RuntimeException re) {
> // Client would have no active connections to the host, hence it
> would encounter a timeout
> // trying to find an alive connection to the host.
> assertThat(re.getCause(),
> instanceOf(NoHostAvailableException.class));
> //
> // should recover when the server comes back
> //
> // restart server
> this.startServer();
> // try a bunch of times to reconnect. on slower systems this may
> simply take longer...looking at you travis
> for (int ix = 1; ix < 11; ix++) {
> // the retry interval is 1 second, wait a bit longer
> TimeUnit.SECONDS.sleep(5);
> try {
> final List<Result> results =
> client.submit("1+1").all().get(3000, TimeUnit.MILLISECONDS);
> assertEquals(1, results.size());
> assertEquals(2, results.get(0).getInt());
> } catch (Exception ex) {
> if (ix == 10)
> fail("Should have eventually succeeded");
> }
> }
> } finally {
> cluster.close();
> }
> }
> {code}
> Note that there is a similar test that first allows a connect to a host and
> then kills it and then restarts it again called {{shouldFailOnDeadHost()}}
> which demonstrates that reconnection works in that situation.
> I thought it might be an easy to fix to simply call
> {{considerHostUnavailable()}} in the {{ConnectionPool}} constructor in the
> event of a {{CompletionException}} which should kickstart the reconnect
> process. The reconnects started firing but they all failed for some reason. I
> didn't have time to investigate further than than.
> Currently the only workaround is to recreate the `Client` if this sort of
> situation occurs.
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