diff --git a/zuul/driver/gerrit/gerritconnection.py b/zuul/driver/gerrit/gerritconnection.py
index f7e509b34a..8502940c70 100644
--- a/zuul/driver/gerrit/gerritconnection.py
+++ b/zuul/driver/gerrit/gerritconnection.py
@@ -41,7 +41,7 @@ from zuul.driver.gerrit.gcloudauth import GCloudAuth
 from zuul.driver.gerrit.gerritmodel import GerritChange, GerritTriggerEvent
 from zuul.driver.git.gitwatcher import GitWatcher
 from zuul.lib.logutil import get_annotated_logger
-from zuul.model import Ref, Tag, Branch, Project
+from zuul.model import Ref, Tag, Branch, Project, CacheStat
 from zuul.zk.event_queues import ConnectionEventQueue, EventReceiverElection
 
 # HTTP timeout in seconds
@@ -798,6 +798,8 @@ class GerritConnection(BaseConnection):
             change = GerritChange(None)
             change.number = number
             change.patchset = patchset
+        change.cache_stat = CacheStat((change.number, change.patchset),
+                                      None, None)
         self._change_cache.setdefault(change.number, {})
         self._change_cache[change.number][change.patchset] = change
         try:
@@ -902,8 +904,8 @@ class GerritConnection(BaseConnection):
             # already merged. So even if it is "ABANDONED", we should not
             # ignore it.
             if (not dep.is_merged) and dep not in needs_changes:
-                git_needs_changes.append(dep)
-                needs_changes.add(dep)
+                git_needs_changes.append(dep.cache_key)
+                needs_changes.add(dep.cache_key)
         change.git_needs_changes = git_needs_changes
 
         compat_needs_changes = []
@@ -914,8 +916,8 @@ class GerritConnection(BaseConnection):
             dep = self._getChange(dep_num, dep_ps, history=history,
                                   event=event)
             if dep.open and dep not in needs_changes:
-                compat_needs_changes.append(dep)
-                needs_changes.add(dep)
+                compat_needs_changes.append(dep.cache_key)
+                needs_changes.add(dep.cache_key)
         change.compat_needs_changes = compat_needs_changes
 
         needed_by_changes = set()
@@ -928,8 +930,8 @@ class GerritConnection(BaseConnection):
                                       event=event)
                 if (dep.open and dep.is_current_patchset and
                     dep not in needed_by_changes):
-                    git_needed_by_changes.append(dep)
-                    needed_by_changes.add(dep)
+                    git_needed_by_changes.append(dep.cache_key)
+                    needed_by_changes.add(dep.cache_key)
             except Exception:
                 log.exception("Failed to get git-needed change %s,%s",
                               dep_num, dep_ps)
@@ -952,13 +954,20 @@ class GerritConnection(BaseConnection):
                     event=event)
                 if (dep.open and dep.is_current_patchset
                     and dep not in needed_by_changes):
-                    compat_needed_by_changes.append(dep)
-                    needed_by_changes.add(dep)
+                    compat_needed_by_changes.append(dep.cache_key)
+                    needed_by_changes.add(dep.cache_key)
             except Exception:
                 log.exception("Failed to get commit-needed change %s,%s",
                               dep_num, dep_ps)
         change.compat_needed_by_changes = compat_needed_by_changes
 
+    def getChangeByKey(self, key):
+        try:
+            number, patchset = key
+            return self._change_cache[number][patchset]
+        except (KeyError, ValueError):
+            return None
+
     def isMerged(self, change, head=None):
         self.log.debug("Checking if change %s is merged" % change)
         if not change.number:
diff --git a/zuul/driver/gerrit/gerritsource.py b/zuul/driver/gerrit/gerritsource.py
index 50f71d9ed5..7c18ef8710 100644
--- a/zuul/driver/gerrit/gerritsource.py
+++ b/zuul/driver/gerrit/gerritsource.py
@@ -81,6 +81,9 @@ class GerritSource(BaseSource):
             event=event)
         return change
 
+    def getChangeByKey(self, key):
+        return self.connection.getChangeByKey(key)
+
     def getChangesDependingOn(self, change, projects, tenant):
         changes = []
         if not change.uris:
diff --git a/zuul/driver/github/githubconnection.py b/zuul/driver/github/githubconnection.py
index 598bfc0345..7a8bac6724 100644
--- a/zuul/driver/github/githubconnection.py
+++ b/zuul/driver/github/githubconnection.py
@@ -44,7 +44,7 @@ from zuul.connection import CachedBranchConnection
 from zuul.driver.github.graphql import GraphQLClient
 from zuul.web.handler import BaseWebController
 from zuul.lib.logutil import get_annotated_logger
-from zuul.model import Ref, Branch, Tag, Project
+from zuul.model import Ref, Branch, Tag, Project, CacheStat
 from zuul.exceptions import MergeFailure
 from zuul.driver.github.githubmodel import PullRequest, GithubTriggerEvent
 from zuul.model import DequeueEvent
@@ -1307,6 +1307,7 @@ class GithubConnection(CachedBranchConnection):
             if lock.acquire(blocking=False):
                 try:
                     self._updateChange(change, event)
+                    change.cache_stat = CacheStat(key, None, None)
                     self._change_cache[key] = change
 
                     if self.sched:
@@ -1331,6 +1332,9 @@ class GithubConnection(CachedBranchConnection):
             raise
         return change
 
+    def getChangeByKey(self, key):
+        return self._change_cache.get(key)
+
     def getChangesDependingOn(self, change, projects, tenant):
         changes = []
         if not change.uris:
diff --git a/zuul/driver/github/githubsource.py b/zuul/driver/github/githubsource.py
index 3028bb52aa..1b23401ff1 100644
--- a/zuul/driver/github/githubsource.py
+++ b/zuul/driver/github/githubsource.py
@@ -95,6 +95,9 @@ class GithubSource(BaseSource):
             event=event)
         return change
 
+    def getChangeByKey(self, key):
+        return self.connection.getChangeByKey(key)
+
     def getChangesDependingOn(self, change, projects, tenant):
         return self.connection.getChangesDependingOn(change, projects, tenant)
 
diff --git a/zuul/driver/gitlab/gitlabconnection.py b/zuul/driver/gitlab/gitlabconnection.py
index 35f1f282ae..b6e6f6e50d 100644
--- a/zuul/driver/gitlab/gitlabconnection.py
+++ b/zuul/driver/gitlab/gitlabconnection.py
@@ -32,7 +32,7 @@ from zuul.connection import CachedBranchConnection
 from zuul.web.handler import BaseWebController
 from zuul.lib.logutil import get_annotated_logger
 from zuul.exceptions import MergeFailure
-from zuul.model import Branch, Project, Ref, Tag
+from zuul.model import Branch, CacheStat, Project, Ref, Tag
 from zuul.driver.gitlab.gitlabmodel import GitlabTriggerEvent, MergeRequest
 from zuul.zk.event_queues import ConnectionEventQueue
 
@@ -535,6 +535,7 @@ class GitlabConnection(CachedBranchConnection):
             change.patchset = patch_number
             change.url = url or self.getMRUrl(project.name, number)
             change.uris = [change.url.split('://', 1)[-1]]  # remove scheme
+        change.cache_stat = CacheStat(key, None, None)
         self._change_cache[key] = change
         try:
             log.debug("Getting change mr#%s from project %s" % (
@@ -614,6 +615,9 @@ class GitlabConnection(CachedBranchConnection):
                 "Set approval: %s on MR %s#%s (%s)", approve,
                 project_name, number, patchset)
 
+    def getChangeByKey(self, key):
+        return self._change_cache.get(key)
+
     def getChangesDependingOn(self, change, projects, tenant):
         """ Reverse lookup of MR depending on this one
         """
diff --git a/zuul/driver/gitlab/gitlabsource.py b/zuul/driver/gitlab/gitlabsource.py
index 9296c641c9..fbd582367f 100644
--- a/zuul/driver/gitlab/gitlabsource.py
+++ b/zuul/driver/gitlab/gitlabsource.py
@@ -82,6 +82,9 @@ class GitlabSource(BaseSource):
             event=event)
         return change
 
+    def getChangeByKey(self, key):
+        return self.connection.getChangeByKey(key)
+
     def getChangesDependingOn(self, change, projects, tenant):
         return self.connection.getChangesDependingOn(
             change, projects, tenant)
diff --git a/zuul/driver/pagure/pagureconnection.py b/zuul/driver/pagure/pagureconnection.py
index e65a329b89..4c7e762073 100644
--- a/zuul/driver/pagure/pagureconnection.py
+++ b/zuul/driver/pagure/pagureconnection.py
@@ -26,7 +26,7 @@ import voluptuous as v
 from zuul.connection import BaseConnection
 from zuul.lib.logutil import get_annotated_logger
 from zuul.web.handler import BaseWebController
-from zuul.model import Ref, Branch, Tag
+from zuul.model import Ref, Branch, Tag, CacheStat
 from zuul.lib import dependson
 from zuul.zk.event_queues import ConnectionEventQueue
 
@@ -626,6 +626,7 @@ class PagureConnection(BaseConnection):
             change.uris = [
                 '%s/%s/pull/%s' % (self.baseurl, project, number),
             ]
+        change.cache_stat = CacheStat(key, None, None)
         self._change_cache[key] = change
         try:
             self.log.debug("Getting change pr#%s from project %s" % (
@@ -762,6 +763,9 @@ class PagureConnection(BaseConnection):
                 number, project, flag.get('status')))
         return flag.get('status')
 
+    def getChangeByKey(self, key):
+        return self._change_cache.get(key)
+
     def getChangesDependingOn(self, change, projects, tenant):
         """ Reverse lookup of PR depending on this one
         """
diff --git a/zuul/driver/pagure/paguresource.py b/zuul/driver/pagure/paguresource.py
index 78a62b911f..4202df070d 100644
--- a/zuul/driver/pagure/paguresource.py
+++ b/zuul/driver/pagure/paguresource.py
@@ -88,6 +88,9 @@ class PagureSource(BaseSource):
             event=event)
         return change
 
+    def getChangeByKey(self, key):
+        return self.connection.getChangeByKey(key)
+
     def getChangesDependingOn(self, change, projects, tenant):
         return self.connection.getChangesDependingOn(
             change, projects, tenant)
diff --git a/zuul/driver/zuul/__init__.py b/zuul/driver/zuul/__init__.py
index afbee1bd0c..390b65b79c 100644
--- a/zuul/driver/zuul/__init__.py
+++ b/zuul/driver/zuul/__init__.py
@@ -111,7 +111,8 @@ class ZuulDriver(Driver, TriggerInterface):
         # This is very inefficient, especially on systems with large
         # numbers of github installations.  This can be improved later
         # with persistent storage of dependency information.
-        needed_by_changes = set(change.needed_by_changes)
+        needed_by_changes = set(
+            pipeline.manager.resolveChangeKeys(change.needed_by_changes))
         for source in self.sched.connections.getSources():
             log.debug("  Checking source: %s", source)
             needed_by_changes.update(
diff --git a/zuul/manager/__init__.py b/zuul/manager/__init__.py
index 70174079a6..83aedbe9d2 100644
--- a/zuul/manager/__init__.py
+++ b/zuul/manager/__init__.py
@@ -10,6 +10,7 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 import collections
+import contextlib
 import logging
 import textwrap
 import time
@@ -61,6 +62,9 @@ class PipelineManager(metaclass=ABCMeta):
         # Cached dynamic layouts (layout uuid -> layout)
         self._layout_cache = {}
         self.sql = self.sched.sql
+        # A small local cache to avoid hitting the ZK-based connection
+        # change cache for multiple hits in the same pipeline run.
+        self._change_cache = {}
 
     def __str__(self):
         return "<%s %s>" % (self.__class__.__name__, self.pipeline.name)
@@ -150,6 +154,44 @@ class PipelineManager(metaclass=ABCMeta):
                  i.live]
         return items.index(item)
 
+    def resolveChangeKeys(self, change_keys):
+        resolved_changes = []
+        for key in change_keys:
+            change = self._change_cache.get(key)
+            if change is None:
+                connection_name, connection_key = key
+                source = self.sched.connections.getSource(connection_name)
+                change = source.getChangeByKey(connection_key)
+                self._change_cache[change.cache_key] = change
+            resolved_changes.append(change)
+        return resolved_changes
+
+    def _maintainCache(self):
+        active_layout_uuids = set()
+        referenced_change_keys = set()
+        for item in self.pipeline.getAllItems():
+            if item.layout_uuid:
+                active_layout_uuids.add(item.layout_uuid)
+
+            if isinstance(item.change, model.Change):
+                referenced_change_keys.update(item.change.needs_changes)
+                referenced_change_keys.update(item.change.needed_by_changes)
+
+        # Clean up unused layouts in the cache
+        unused_layouts = set(self._layout_cache.keys()) - active_layout_uuids
+        if unused_layouts:
+            self.log.debug("Removing unused layouts %s from cache",
+                           unused_layouts)
+            for uid in unused_layouts:
+                with contextlib.suppress(KeyError):
+                    del self._layout_cache[uid]
+
+        # Clean up change cache
+        unused_keys = set(self._change_cache.keys()) - referenced_change_keys
+        for key in unused_keys:
+            with contextlib.suppress(KeyError):
+                del self._change_cache[key]
+
     def isChangeAlreadyInPipeline(self, change):
         # Checks live items in the pipeline
         for item in self.pipeline.getAllItems():
@@ -623,7 +665,7 @@ class PipelineManager(metaclass=ABCMeta):
             change.project.connection_name)
         source.setChangeAttributes(
             change,
-            commit_needs_changes=[d for d in dependencies],
+            commit_needs_changes=[d.cache_key for d in dependencies],
             refresh_deps=False)
 
     def provisionNodes(self, item):
@@ -1350,17 +1392,7 @@ class PipelineManager(metaclass=ABCMeta):
                     self.log.debug("Queue %s status is now:\n %s" %
                                    (queue.name, status))
 
-        # Cleanup unused layouts in the cache
-        active_layout_uuids = {i.layout_uuid
-                               for i in self.pipeline.getAllItems()
-                               if i.layout_uuid}
-        unused_layouts = set(self._layout_cache.keys()) - active_layout_uuids
-        if unused_layouts:
-            self.log.debug("Removing unused layouts %s from cache",
-                           unused_layouts)
-        for uid in unused_layouts:
-            del self._layout_cache[uid]
-
+        self._maintainCache()
         self.log.debug("Finished queue processor: %s (changed: %s)" %
                        (self.pipeline.name, changed))
         return changed
diff --git a/zuul/manager/dependent.py b/zuul/manager/dependent.py
index 7b6667fef4..750a272090 100644
--- a/zuul/manager/dependent.py
+++ b/zuul/manager/dependent.py
@@ -85,8 +85,8 @@ class DependentPipelineManager(SharedQueuePipelineManager):
         for project, _ in change_queue.project_branches:
             sources.add(project.source)
 
-        seen = set(change.needed_by_changes)
-        needed_by_changes = change.needed_by_changes[:]
+        needed_by_changes = self.resolveChangeKeys(change.needed_by_changes)
+        seen = set(needed_by_changes)
         for source in sources:
             log.debug("  Checking source: %s", source)
             projects = [project_branch[0]
@@ -157,7 +157,7 @@ class DependentPipelineManager(SharedQueuePipelineManager):
             # a git level dependency, we need to enqueue it before the current
             # change.
             if (needed_change not in history or
-                needed_change in change.git_needs_changes):
+                    needed_change.cache_key in change.git_needs_changes):
                 r = self.addChange(needed_change, event, quiet=quiet,
                                    ignore_requirements=ignore_requirements,
                                    change_queue=change_queue, history=history,
@@ -185,7 +185,7 @@ class DependentPipelineManager(SharedQueuePipelineManager):
         changes_needed = []
         # Ignore supplied change_queue
         with self.getChangeQueue(change, event) as change_queue:
-            for needed_change in change.needs_changes:
+            for needed_change in self.resolveChangeKeys(change.needs_changes):
                 log.debug("  Change %s needs change %s:" % (
                     change, needed_change))
                 if needed_change.is_merged:
@@ -234,7 +234,7 @@ class DependentPipelineManager(SharedQueuePipelineManager):
         if not item.change.needs_changes:
             return None
         failing_items = set()
-        for needed_change in item.change.needs_changes:
+        for needed_change in self.resolveChangeKeys(item.change.needs_changes):
             needed_item = self.getItemForChange(needed_change)
             if not needed_item:
                 continue
diff --git a/zuul/manager/independent.py b/zuul/manager/independent.py
index 7686d5a7d4..61aede3c68 100644
--- a/zuul/manager/independent.py
+++ b/zuul/manager/independent.py
@@ -86,7 +86,7 @@ class IndependentPipelineManager(PipelineManager):
             log.debug("  No changes needed")
             return True
         changes_needed = []
-        for needed_change in change.needs_changes:
+        for needed_change in self.resolveChangeKeys(change.needs_changes):
             log.debug("  Change %s needs change %s:" % (
                 change, needed_change))
             if needed_change.is_merged:
diff --git a/zuul/model.py b/zuul/model.py
index 73ad5c0624..8fd57fbdec 100644
--- a/zuul/model.py
+++ b/zuul/model.py
@@ -14,7 +14,7 @@
 # under the License.
 
 import abc
-from collections import OrderedDict, defaultdict, UserDict
+from collections import OrderedDict, defaultdict, namedtuple, UserDict
 import copy
 import json
 import logging
@@ -3538,6 +3538,10 @@ class Bundle:
         return any(i.change.updatesConfig(tenant) for i in self.items)
 
 
+# Cache info of a ref
+CacheStat = namedtuple("CacheStat", ["key", "uuid", "version"])
+
+
 class Ref(object):
     """An existing state of a Project."""
 
@@ -3547,6 +3551,13 @@ class Ref(object):
         self.oldrev = None
         self.newrev = None
         self.files = []
+        # Cache info about this ref:
+        # CacheStat(cache key, uuid, version)
+        self.cache_stat = None
+
+    @property
+    def cache_key(self):
+        return (self.project.connection_name, self.cache_stat.key)
 
     def _id(self):
         return self.newrev
diff --git a/zuul/reporter/__init__.py b/zuul/reporter/__init__.py
index 014dc93432..07a5960f7e 100644
--- a/zuul/reporter/__init__.py
+++ b/zuul/reporter/__init__.py
@@ -223,8 +223,10 @@ class BaseReporter(object, metaclass=abc.ABCMeta):
         return msg
 
     def _formatItemReportOtherBundleItems(self, item):
+        related_changes = item.pipeline.manager.resolveChangeKeys(
+            item.change.needs_changes)
         return "Related changes:\n{}".format("\n".join(
-            c.url for c in item.change.needs_changes if c is not item.change))
+            c.url for c in related_changes if c is not item.change))
 
     def _getItemReportJobsFields(self, item):
         # Extract the report elements from an item
diff --git a/zuul/scheduler.py b/zuul/scheduler.py
index 0afc3555aa..54540be552 100644
--- a/zuul/scheduler.py
+++ b/zuul/scheduler.py
@@ -2190,7 +2190,9 @@ class Scheduler(threading.Thread):
             for other_change in source.getCachedChanges():
                 if other_change.commit_needs_changes is None:
                     continue
-                for dep in other_change.commit_needs_changes:
+                for connection_name, key in other_change.commit_needs_changes:
+                    dep_source = self.connections.getSource(connection_name)
+                    dep = dep_source.getChangeByKey(key)
                     if change.isUpdateOf(dep):
                         source.setChangeAttributes(
                             other_change, refresh_deps=True)
diff --git a/zuul/source/__init__.py b/zuul/source/__init__.py
index d3a11be6ca..b9f73373fb 100644
--- a/zuul/source/__init__.py
+++ b/zuul/source/__init__.py
@@ -76,6 +76,14 @@ class BaseSource(object, metaclass=abc.ABCMeta):
 
         """
 
+    def getChangeByKey(self, key):
+        """Get the change corresponding to the supplied cache key.
+
+        The key may not correspond to this source. Return None if it
+        doesn't.
+        """
+        raise NotImplementedError
+
     @abc.abstractmethod
     def getChangesDependingOn(self, change, projects, tenant):
         """Return changes which depend on changes at the supplied URIs.