diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -3017,6 +3017,7 @@
     'PhabricatorGDSetupCheck' => 'applications/config/check/PhabricatorGDSetupCheck.php',
     'PhabricatorGarbageCollector' => 'infrastructure/daemon/garbagecollector/PhabricatorGarbageCollector.php',
     'PhabricatorGarbageCollectorManagementCollectWorkflow' => 'infrastructure/daemon/garbagecollector/management/PhabricatorGarbageCollectorManagementCollectWorkflow.php',
+    'PhabricatorGarbageCollectorManagementCompactEdgesWorkflow' => 'infrastructure/daemon/garbagecollector/management/PhabricatorGarbageCollectorManagementCompactEdgesWorkflow.php',
     'PhabricatorGarbageCollectorManagementSetPolicyWorkflow' => 'infrastructure/daemon/garbagecollector/management/PhabricatorGarbageCollectorManagementSetPolicyWorkflow.php',
     'PhabricatorGarbageCollectorManagementWorkflow' => 'infrastructure/daemon/garbagecollector/management/PhabricatorGarbageCollectorManagementWorkflow.php',
     'PhabricatorGeneralCachePurger' => 'applications/cache/purger/PhabricatorGeneralCachePurger.php',
@@ -8484,6 +8485,7 @@
     'PhabricatorGDSetupCheck' => 'PhabricatorSetupCheck',
     'PhabricatorGarbageCollector' => 'Phobject',
     'PhabricatorGarbageCollectorManagementCollectWorkflow' => 'PhabricatorGarbageCollectorManagementWorkflow',
+    'PhabricatorGarbageCollectorManagementCompactEdgesWorkflow' => 'PhabricatorGarbageCollectorManagementWorkflow',
     'PhabricatorGarbageCollectorManagementSetPolicyWorkflow' => 'PhabricatorGarbageCollectorManagementWorkflow',
     'PhabricatorGarbageCollectorManagementWorkflow' => 'PhabricatorManagementWorkflow',
     'PhabricatorGeneralCachePurger' => 'PhabricatorCachePurger',
diff --git a/src/infrastructure/daemon/garbagecollector/management/PhabricatorGarbageCollectorManagementCompactEdgesWorkflow.php b/src/infrastructure/daemon/garbagecollector/management/PhabricatorGarbageCollectorManagementCompactEdgesWorkflow.php
new file mode 100644
--- /dev/null
+++ b/src/infrastructure/daemon/garbagecollector/management/PhabricatorGarbageCollectorManagementCompactEdgesWorkflow.php
@@ -0,0 +1,103 @@
+<?php
+
+final class PhabricatorGarbageCollectorManagementCompactEdgesWorkflow
+  extends PhabricatorGarbageCollectorManagementWorkflow {
+
+  protected function didConstruct() {
+    $this
+      ->setName('compact-edges')
+      ->setExamples('**compact-edges**')
+      ->setSynopsis(
+        pht(
+          'Rebuild old edge transactions storage to use a more compact '.
+          'format.'))
+      ->setArguments(array());
+  }
+
+  public function execute(PhutilArgumentParser $args) {
+    $tables = id(new PhutilClassMapQuery())
+      ->setAncestorClass('PhabricatorApplicationTransaction')
+      ->execute();
+
+    foreach ($tables as $table) {
+      $this->compactEdges($table);
+    }
+
+    return 0;
+  }
+
+  private function compactEdges(PhabricatorApplicationTransaction $table) {
+    $conn = $table->establishConnection('w');
+    $class = get_class($table);
+
+    echo tsprintf(
+      "%s\n",
+      pht(
+        'Rebuilding transactions for "%s"...',
+        $class));
+
+    $cursor = 0;
+    $updated = 0;
+    while (true) {
+      $rows = $table->loadAllWhere(
+        'transactionType = %s
+          AND id > %d
+          AND (oldValue LIKE %> OR newValue LIKE %>)
+          ORDER BY id ASC LIMIT 100',
+        PhabricatorTransactions::TYPE_EDGE,
+        $cursor,
+        // We're looking for transactions with JSON objects in their value
+        // fields: the new style transactions have JSON lists instead and
+        // start with "[" rather than "{".
+        '{',
+        '{');
+
+      if (!$rows) {
+        break;
+      }
+
+      foreach ($rows as $row) {
+        $id = $row->getID();
+
+        $old = $row->getOldValue();
+        $new = $row->getNewValue();
+
+        if (!is_array($old) || !is_array($new)) {
+          echo tsprintf(
+            "%s\n",
+            pht(
+              'Transaction %s (of type %s) has unexpected data, skipping.',
+              $id,
+              $class));
+        }
+
+        $record = PhabricatorEdgeChangeRecord::newFromTransaction($row);
+
+        $old_data = $record->getModernOldEdgeTransactionData();
+        $old_json = phutil_json_encode($old_data);
+
+        $new_data = $record->getModernNewEdgeTransactionData();
+        $new_json = phutil_json_encode($new_data);
+
+        queryfx(
+          $conn,
+          'UPDATE %T SET oldValue = %s, newValue = %s WHERE id = %d',
+          $table->getTableName(),
+          $old_json,
+          $new_json,
+          $id);
+
+        $updated++;
+
+        $cursor = $row->getID();
+      }
+    }
+
+    echo tsprintf(
+      "%s\n",
+      pht(
+        'Done, compacted %s edge transactions.',
+        new PhutilNumber($updated)));
+  }
+
+}