From 4e914184586bff7ee3ac8120161df770e75442a1 Mon Sep 17 00:00:00 2001
From: "James E. Blair" <jeblair@redhat.com>
Date: Wed, 18 Oct 2017 17:30:19 -0700
Subject: [PATCH] Remove old buildsets

Buildsets contain references to the dependent items at the time
they were created.  If an item is re-enqueued due to reconfiguration,
(or any other circumstance about the item's position in the pipeline
changes), a new buildset will be created, and the item updated.  Old
buildsets are kept around as an attribute of the item.

The layout is an attribute of the item, and during reconfiguration,
all items currently in pipelines are updated, so we won't have stale
layouts on these items.  However, previous build sets may have
lists of dependent items which, if they are no longer currently in
a pipeline, will not have been updated.  Old build sets may have much
longer lists of dependent items than the current build set.  In fact,
with the right timing for adding new entries to a dependent pipeline
and reconfigurations, an infinite chain of overlapping dependent item
lists could be constructed.

By dropping references to previous buildsets, we can drop references
to old layouts sooner because the dependent items list on current
build sets should generally not grow without bound, and only contain
a moderate number of references to items no longer in pipelines.

An idea for a future change would be to look into whether the dependent
items list could be deleted sooner, or the cost of maintining it
reduced.

Change-Id: I958e1feabda24ae61d66f6b4dc36442c6d0a606b
---
 zuul/model.py | 9 ---------
 1 file changed, 9 deletions(-)

diff --git a/zuul/model.py b/zuul/model.py
index 464ee16dbb..7d6e80c4b8 100644
--- a/zuul/model.py
+++ b/zuul/model.py
@@ -1263,8 +1263,6 @@ class BuildSet(object):
         self.item = item
         self.builds = {}
         self.result = None
-        self.next_build_set = None
-        self.previous_build_set = None
         self.uuid = None
         self.commit = None
         self.dependent_items = None
@@ -1402,10 +1400,8 @@ class QueueItem(object):
         self.pipeline = queue.pipeline
         self.queue = queue
         self.change = change  # a ref
-        self.build_sets = []
         self.dequeued_needing_change = False
         self.current_build_set = BuildSet(self)
-        self.build_sets.append(self.current_build_set)
         self.item_ahead = None
         self.items_behind = []
         self.enqueue_time = None
@@ -1427,12 +1423,7 @@ class QueueItem(object):
             id(self), self.change, pipeline)
 
     def resetAllBuilds(self):
-        old = self.current_build_set
-        self.current_build_set.result = 'CANCELED'
         self.current_build_set = BuildSet(self)
-        old.next_build_set = self.current_build_set
-        self.current_build_set.previous_build_set = old
-        self.build_sets.append(self.current_build_set)
         self.layout = None
         self.job_graph = None