> On June 1, 2017, 8:58 p.m., Alejandro Fernandez wrote: > > ambari-server/src/main/java/org/apache/ambari/server/stageplanner/RoleGraph.java > > Lines 342 (patched) > > <https://reviews.apache.org/r/59727/diff/1/?file=1738985#file1738985line342> > > > > Btw, this will only find cycles between two adjacent nodes. It will not > > find cycles involved with 3 nodes, e.g., > > > > A -> B > > B -> C > > C -> A > > > > This needs a 2-pass depth-first traversal or Tarjan's algorithm. > > Di Li wrote: > My tests showed that Ambari is able to break long chains of dependencies > to short chains that represents cycle graphs of two nodes. This behavior > makes it easier to detect circular dependencies via current logic.
Let's add a unit test for it, Storm depends on Kafka which depends on ZK. So if we then add ZK depends on Storm, that would create a cycle. - Alejandro ----------------------------------------------------------- This is an automatically generated e-mail. To reply, visit: https://reviews.apache.org/r/59727/#review176659 ----------------------------------------------------------- On June 6, 2017, 7:02 p.m., Di Li wrote: > > ----------------------------------------------------------- > This is an automatically generated e-mail. To reply, visit: > https://reviews.apache.org/r/59727/ > ----------------------------------------------------------- > > (Updated June 6, 2017, 7:02 p.m.) > > > Review request for Ambari and Tim Thorpe. > > > Bugs: AMBARI-21161 > https://issues.apache.org/jira/browse/AMBARI-21161 > > > Repository: ambari > > > Description > ------- > > It is important to safe guard against cycle graphs, when Ambari supports > mpacks, custom services and service level role command order. Cycle graphs > indicate circular dependencies that can cause Ambari enter an infinite loop > while building stages, causing Ambari server to take up 100% CPU and large > amount of memory. > > > Diffs > ----- > > > ambari-server/src/main/java/org/apache/ambari/server/stageplanner/RoleGraph.java > 024a5e1 > > ambari-server/src/test/java/org/apache/ambari/server/stageplanner/TestStagePlanner.java > 271ee89 > ambari-server/src/test/resources/stacks/HDP/2.0.6.1/role_command_order.json > 6154004 > > > Diff: https://reviews.apache.org/r/59727/diff/2/ > > > Testing > ------- > > unit tests. patch a trunk cluster with code change and install HDP cluster, > intentionally add circular reference to make NN start depends on DN start > and DN start depends on NN start. Verify UI shows an error message when try > to start HDFS service, and does not really kick off the HDFS start. (without > the fix, Ambari server will try to start HDFS and gets itself into an > infinite loop and uses up 100% CPU and large amount of RAM) > > > Thanks, > > Di Li > >
