----------------------------------------------------------- This is an automatically generated e-mail. To reply, visit: https://reviews.apache.org/r/37356/#review94991 -----------------------------------------------------------
ambari-server/src/main/java/org/apache/ambari/server/topology/TopologyManager.java (line 169) <https://reviews.apache.org/r/37356/#comment149740> Just got done discussing with Bob on a call. This synchronized block should be moved up to line 153 and end at the bottom of the method. The existing availbleHosts synchronization block on line 195 should be removed due to the existence of the new availableHosts syncronization described above. The important thing here is that we synchronize on a common mutual exclusion monitor in both onHostRegistered and processRequest. With this patch it will be the availableHosts monitor. I agree with the other comments that this is dangerous any likely inefficient and also agree that we should change as little as possible initially while still fixing the issue. If this patch causes a significant performance degradation then we can then look at optimizing the locking in this class in another patch. - John Speidel On Aug. 11, 2015, 3:30 p.m., Robert Nettleton wrote: > > ----------------------------------------------------------- > This is an automatically generated e-mail. To reply, visit: > https://reviews.apache.org/r/37356/ > ----------------------------------------------------------- > > (Updated Aug. 11, 2015, 3:30 p.m.) > > > Review request for Ambari, Jonathan Hurley, John Speidel, Mahadev Konar, > Robert Levas, and Sumit Mohanty. > > > Bugs: AMBARI-12720 > https://issues.apache.org/jira/browse/AMBARI-12720 > > > Repository: ambari > > > Description > ------- > > This patch provides a fix for AMBARI-12720. > > Blueprint Cluster deployments are failing under load, with clusters of 50+ > nodes. One or more hosts in the cluster fail to be registered, even though > the ambari-agent registration occurs properly for these hosts. This problem > seems to occur when certain hosts are registered at roughly the same time as > the call to TopologyManager.processRequest(). > > Upon further analysis, it appears that the > TopologyManager.outstandingRequests object is not fully sychronized. > > There are two paths involved in reading/writing to this data structure: > > 1. TopologyManager.processRequest() (occurs on the main request thread > handling the cluster creation request). When all known hosts have been > processed, but some requests are pending, the LogicalRequest instance is > added to TopologyManager.outstandingRequests. Note: The call to add this > request is not synchronized on the outstandingRequests object, but is only > synchronized on TopologyManager.availableHosts. > 2. TopologyManager.onHostRegistered() (occurs on a separate thread that > handles ambari-agent registrations for new hosts joining the cluster). This > method does synchronize on TopologyManager.outstandingRequests, and attempts > to iterate over these requests to determine if the newly registered host can > satisfy the request. > > The incorrect synchronization on TopologyManager.outstandingRequests appears > to be the root of the intermittent cluster deployment problems described in > AMBARI-12720. Since this datastructure is read/updated by both threads, and > since this object is not protected by the same locks, there appears to be a > race condition in this code. > > To fix this problem, this patch implements the following: > > 1. Updates the TopologyManager.onHostRegistered() method to lock on > --> availableHosts > --> outstandingRequests > prior to reading TopologyManager.outstandingRequests > > 2. Updates the TopologyManager.processRequest() method to lock on > --> availableHosts > --> outstandingRequests > prior to adding a LogicalRequest instance to this collection > > > The locking order (availableHosts, outstandingRequests) must be kept in place > in order to avoid any potential deadlocks from making a change like this. > > > Diffs > ----- > > > ambari-server/src/main/java/org/apache/ambari/server/topology/TopologyManager.java > 8e7fb7f > > Diff: https://reviews.apache.org/r/37356/diff/ > > > Testing > ------- > > 1. Ran the ambari-server unit test suite ("mvn clean test"). All tests are > passing. > 2. Deployed a 3-node HDFS HA cluster via a Blueprint, to make sure this > change does not break existing deployments. > 3. Deployed a 45-node HDFS HA cluster via a Blueprint on the cloud, to make > sure this change does not break deployments of larger clusters. > > > Thanks, > > Robert Nettleton > >
