Many thanks to everyone who helped with the many fixes. Kudos to Joe/Clark for spear heading the effort!
-- dims On Mon, Nov 25, 2013 at 12:00 AM, Joe Gordon <joe.gord...@gmail.com> wrote: > Hi All, > > TL;DR Last week the gate got wedged on nondeterministic failures. Unwedging > the gate required drastic actions to fix bugs. > > Starting on November 15th, gate jobs have been getting progressively less > stable with not enough attention given to fixing the issues, until we got to > the point where the gate was almost fully wedged. No one bug caused this, > it was a collection of bugs that got us here. The gate protects us from code > that fails 100% of the time, but if a patch fails 10% of the time it can > slip through. Add a few of these bugs together and we get the gate to a > point where the gate is fully wedged and fixing it without circumventing the > gate (something we never want to do) is very hard. It took just 2 new > nondeterministic bugs to take us from a gate that mostly worked, to a gate > that was almost fully wedged. Last week we found out Jeremy Stanley (fungi) > was right when he said, "nondeterministic failures breed more > nondeterministic failures, because people are so used to having to reverify > their patches to get them to merge that they are doing so even when it's > their patch which is introducing a nondeterministic bug." > > Side note: This is not the first time we wedge the gate, the first time was > around September 26th, right when we were cutting Havana release candidates. > In response we wrote elastic-recheck > (http://status.openstack.org/elastic-recheck/) to better track what bugs we > were seeing. > > Gate stability according to Graphite: http://paste.openstack.org/show/53765/ > (they are huge because they encode entire queries, so including as a > pastebin). > > After sending out an email to ask for help fixing the top known gate bugs > (http://lists.openstack.org/pipermail/openstack-dev/2013-November/019826.html), > we had a few possible fixes. But with the gate wedged, the merge queue was > 145 patches long and could take days to be processed. In the worst case, > none of the patches merging, it would take about 1 hour per patch. So on > November 20th we asked for a freeze on any non-critical bug fixes ( > http://lists.openstack.org/pipermail/openstack-dev/2013-November/019941.html > ), and kicked everything out of the merge queue and put our possible bug > fixes at the front. Even with these drastic measures it still took 26 hours > to finally unwedge the gate. In 26 hours we got the check queue failure rate > (always higher then the gate failure rate) down from around 87% failure to > below 10% failure. And we still have many more bugs to track down and fix in > order to improve gate stability. > > > 8 Major bug fixes later, we have the gate back to a reasonable failure rate. > But how did things get so bad? I'm glad you asked, here is a blow by blow > account. > > The gate has not been completely stable for a very long time, and it only > took two new bugs to wedge the gate. Starting with the list of bugs we > identified via elastic-recheck, we fixed 4 bugs that have been in the gate > for a few weeks already. > > > https://bugs.launchpad.net/bugs/1224001 "test_network_basic_ops fails > waiting for network to become available" > > https://review.openstack.org/57290 was the fix which depended on > https://review.openstack.org/53188 and https://review.openstack.org/57475. > > This fixed a race condition where the IP address from DHCP was not received > by the VM at the right time. Minimize polling on the agent is now defaulted > to True, which should reduce the time needed for configuring an interface on > br-int consistently. > > https://bugs.launchpad.net/bugs/1252514 "Swift returning errors when setup > using devstack" > > Fix https://review.openstack.org/#/c/57373/ > > There were a few swift related problems that were sorted out as well. Most > had to do with tuning swift properly for its use as a glance backend in the > gate, ensuring that timeout values were appropriate for the devstack test > slaves (in > > resource constrained environments, the swift default timeouts could be > tripped frequently (logs showed the request would have finished successfully > given enough time)). Swift also had a race-condition in how it constructed > its sqlite3 > > files for containers and accounts, where it was not retrying operations when > the database was locked. > > https://bugs.launchpad.net/swift/+bug/1243973 "Simultaneous PUT requests for > the same account..." > > Fix https://review.openstack.org/#/c/57019/ > > This was not on our original list of bugs, but while in bug fix mode, we got > this one fixed as well > > https://bugs.launchpad.net/bugs/1251784 "nova+neutron scheduling error: > Connection to neutron failed: Maximum attempts reached > > Fix https://review.openstack.org/#/c/57509/ > > Uncovered on mailing list > (http://lists.openstack.org/pipermail/openstack-dev/2013-November/019906.html) > > Nova had a very old version of oslo's local.py which is used for managing > references to local variables in coroutines. The old version had a pretty > significant bug that basically meant non-weak references to variables were > not managed properly. This fix has made the nova neutron interactions much > more reliable. > > This fixed the number 2 bug on our list of top gate bugs > (http://lists.openstack.org/pipermail/openstack-dev/2013-November/019826.html > )! > > > In addition to fixing 4 old bugs, we fixed two new bugs that were introduced > / exposed this week. > > https://bugs.launchpad.net/bugs/1251920 "Tempest failures due to failure to > return console logs from an instance Project" > > Bug: https://review.openstack.org/#/c/54363/ [Tempest] > > Fix(work around): https://review.openstack.org/#/c/57193/ > > After many false starts and banging our head against the wall, we identified > a change to tempest, https://review.openstack.org/54363 , that added a new > test around the same time as bug 1251920 became a problem. Forcing tempest > to skip this test had a very high incidence of success without any 1251920 > related failures. As a result we are working arond this bug by skipping that > test, until it can be run without major impact to the gate. > > The change that introduced this problematic test had to go through the gate > four times before it would merge, though only one of the 3 failed attemps > appears to have triggered 1251920. Or as Jeremy Stanley (fungi) said > "nondeterministic failures breed more nondeterministic failures, because > people are so used to having to reverify their patches to get them to merge > that they are doing so even when it's their patch which is introducing a > nondeterministic bug." > > https://bugs.launchpad.net/bugs/1252170 "tempest.scenario > test_resize_server_confirm failed in grenade" > > Fix https://review.openstack.org/#/c/57357/ > > Fix https://review.openstack.org/#/c/57572/ > > First we started running post Grenade upgrade tests in parallel (to fix > another bug) which would normally be fine, but Grenade wasn't configuring > the small flavors typically used by tempest so it was possible for the > devstack Jenkins slaves to run out of memory when starting many larger VMs > in parallel. To fix this devstack lib/tempest has been updated to create the > flavors only if they don't exist and Grenade is allowing tempest to use its > default instance flavors. > > > > Now that we have the gate back into working order, we are working on the > next steps to prevent this from happening again. The two most immediate > changes are: > > Doing a better job of triaging gate bugs > (http://lists.openstack.org/pipermail/openstack-dev/2013-November/020048.html > ). > > In the next few days we will remove 'reverify no bug' (although you will > still be able to run 'reverify bug x'. > > > Best, > Joe Gordon > Clark Boylan > > _______________________________________________ > OpenStack-dev mailing list > OpenStack-dev@lists.openstack.org > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev > -- Davanum Srinivas :: http://davanum.wordpress.com _______________________________________________ OpenStack-dev mailing list OpenStack-dev@lists.openstack.org http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
