diff --git a/src/applications/config/check/PhabricatorBinariesSetupCheck.php b/src/applications/config/check/PhabricatorBinariesSetupCheck.php
--- a/src/applications/config/check/PhabricatorBinariesSetupCheck.php
+++ b/src/applications/config/check/PhabricatorBinariesSetupCheck.php
@@ -120,17 +120,11 @@
           break;
         case PhabricatorRepositoryType::REPOSITORY_TYPE_MERCURIAL:
           $bad_versions = array(
-            // We need 1.9 for HTTP cloning, see T3046.
-            '< 1.9' => pht(
-              'The minimum supported version of Mercurial is 1.9, which was '.
-              'released in 2011.'),
-            '= 2.1' => pht(
-              'This version of Mercurial returns a bad exit code '.
-              'after a successful pull.'),
-            '= 2.2' => pht(
-              'This version of Mercurial has a significant memory leak, fixed '.
-              'in 2.2.1. Pushing fails with this version as well; see %s.',
-              'T3046#54922'),
+            // We need 2.4 for utilizing `{p1node}` keyword in templates, see
+            // D21679 and D21681.
+            '< 2.4' => pht(
+              'The minimum supported version of Mercurial is 2.4, which was '.
+              'released in 2012.'),
           );
           break;
       }
diff --git a/src/applications/diffusion/conduit/DiffusionHistoryQueryConduitAPIMethod.php b/src/applications/diffusion/conduit/DiffusionHistoryQueryConduitAPIMethod.php
--- a/src/applications/diffusion/conduit/DiffusionHistoryQueryConduitAPIMethod.php
+++ b/src/applications/diffusion/conduit/DiffusionHistoryQueryConduitAPIMethod.php
@@ -136,28 +136,33 @@
     // stop history (this is more consistent with the Mercurial worldview of
     // branches).
 
+    $path_args = array();
     if (strlen($path)) {
-      $path_arg = csprintf('%s', $path);
+      $path_args[] = $path;
       $revset_arg = hgsprintf(
         'reverse(ancestors(%s))',
         $commit_hash);
     } else {
-      $path_arg = '';
       $revset_arg = hgsprintf(
         'reverse(ancestors(%s)) and branch(%s)',
         $drequest->getBranch(),
         $commit_hash);
     }
 
+    $hg_analyzer = PhutilBinaryAnalyzer::getForBinary('hg');
+    if ($hg_analyzer->isMercurialTemplatePnodeAvailable()) {
+      $hg_log_template = '{node} {p1.node} {p2.node}\\n';
+    } else {
+      $hg_log_template = '{node} {p1node} {p2node}\\n';
+    }
+
     list($stdout) = $repository->execxLocalCommand(
-      'log --debug --template %s --limit %d --rev %s -- %C',
-      '{node};{parents}\\n',
+      'log --template %s --limit %d --rev %s -- %Ls',
+      $hg_log_template,
       ($offset + $limit), // No '--skip' in Mercurial.
       $revset_arg,
-      $path_arg);
+      $path_args);
 
-    $stdout = DiffusionMercurialCommandEngine::filterMercurialDebugOutput(
-      $stdout);
     $lines = explode("\n", trim($stdout));
     $lines = array_slice($lines, $offset);
 
@@ -166,37 +171,19 @@
 
     $last = null;
     foreach (array_reverse($lines) as $line) {
-      // In the event additional log output is included in future mercurial
-      // updates, if the line does not contain any semi-colon then log it and
-      // ignore it.
-      if (strpos($line, ';') === false) {
-        phlog(pht(
-          'Unexpected output from mercurial "log --debug" command: %s',
-          $line));
-        continue;
-      }
-      list($hash, $parents) = explode(';', $line);
-      $parents = trim($parents);
-      if (!$parents) {
-        if ($last === null) {
-          $parent_map[$hash] = array('...');
-        } else {
-          $parent_map[$hash] = array($last);
-        }
-      } else {
-        $parents = preg_split('/\s+/', $parents);
-        foreach ($parents as $parent) {
-          list($plocal, $phash) = explode(':', $parent);
-          if (!preg_match('/^0+$/', $phash)) {
-            $parent_map[$hash][] = $phash;
-          }
-        }
-        // This may happen for the zeroth commit in repository, both hashes
-        // are "000000000...".
-        if (empty($parent_map[$hash])) {
-          $parent_map[$hash] = array('...');
+      $parts = explode(' ', trim($line));
+      $hash = $parts[0];
+      $parents = array_slice($parts, 1, 2);
+      foreach ($parents as $parent) {
+        if (!preg_match('/^0+\z/', $parent)) {
+          $parent_map[$hash][] = $parent;
         }
       }
+      // This may happen for the zeroth commit in repository, both hashes
+      // are "000000000...".
+      if (empty($parent_map[$hash])) {
+        $parent_map[$hash] = array('...');
+      }
 
       // The rendering code expects the first commit to be "mainline", like
       // Git. Flip the order so it does the right thing.
diff --git a/src/applications/diffusion/protocol/__tests__/DiffusionMercurialCommandEngineTests.php b/src/applications/diffusion/protocol/__tests__/DiffusionMercurialCommandEngineTests.php
--- a/src/applications/diffusion/protocol/__tests__/DiffusionMercurialCommandEngineTests.php
+++ b/src/applications/diffusion/protocol/__tests__/DiffusionMercurialCommandEngineTests.php
@@ -3,6 +3,53 @@
 final class DiffusionMercurialCommandEngineTests extends PhabricatorTestCase {
 
   public function testFilteringDebugOutput() {
+    $map = array(
+      '' => '',
+
+      "quack\n" => "quack\n",
+
+      "ignoring untrusted configuration option x.y = z\nquack\n" =>
+        "quack\n",
+
+      "ignoring untrusted configuration option x.y = z\n".
+      "ignoring untrusted configuration option x.y = z\n".
+      "quack\n" =>
+        "quack\n",
+
+      "ignoring untrusted configuration option x.y = z\n".
+      "ignoring untrusted configuration option x.y = z\n".
+      "ignoring untrusted configuration option x.y = z\n".
+      "quack\n" =>
+        "quack\n",
+
+      "quack\n".
+      "ignoring untrusted configuration option x.y = z\n".
+      "ignoring untrusted configuration option x.y = z\n".
+      "ignoring untrusted configuration option x.y = z\n" =>
+        "quack\n",
+
+      "ignoring untrusted configuration option x.y = z\n".
+      "ignoring untrusted configuration option x.y = z\n".
+      "duck\n".
+      "ignoring untrusted configuration option x.y = z\n".
+      "ignoring untrusted configuration option x.y = z\n".
+      "bread\n".
+      "ignoring untrusted configuration option x.y = z\n".
+      "quack\n" =>
+        "duck\nbread\nquack\n",
+
+      "ignoring untrusted configuration option x.y = z\n".
+      "duckignoring untrusted configuration option x.y = z\n".
+      "quack" =>
+        'duckquack',
+    );
+
+    foreach ($map as $input => $expect) {
+      $actual = DiffusionMercurialCommandEngine::filterMercurialDebugOutput(
+        $input);
+      $this->assertEqual($expect, $actual, $input);
+    }
+
     // Output that should be filtered out from the results
     $output =
       "ignoring untrusted configuration option\n".
diff --git a/src/applications/diffusion/query/blame/DiffusionMercurialBlameQuery.php b/src/applications/diffusion/query/blame/DiffusionMercurialBlameQuery.php
--- a/src/applications/diffusion/query/blame/DiffusionMercurialBlameQuery.php
+++ b/src/applications/diffusion/query/blame/DiffusionMercurialBlameQuery.php
@@ -6,11 +6,26 @@
     $repository = $request->getRepository();
     $commit = $request->getCommit();
 
-    // NOTE: We're using "--debug" to make "--changeset" give us the full
-    // commit hashes.
+    // NOTE: Using "--template" or "--debug" to get the full commit hashes.
+    $hg_analyzer = PhutilBinaryAnalyzer::getForBinary('hg');
+    if ($hg_analyzer->isMercurialAnnotateTemplatesAvailable()) {
+      // See `hg help annotate --verbose` for more info on the template format.
+      // Use array of arguments so the template line does not need wrapped in
+      // quotes.
+      $template = array(
+        '--template',
+        "{lines % '{node}: {line}'}",
+      );
+    } else {
+      $template = array(
+        '--debug',
+        '--changeset',
+      );
+    }
 
     return $repository->getLocalCommandFuture(
-      'annotate --debug --changeset --rev %s -- %s',
+      'annotate %Ls --rev %s -- %s',
+      $template,
       $commit,
       $path);
   }
@@ -26,6 +41,21 @@
 
     $lines = phutil_split_lines($stdout);
     foreach ($lines as $line) {
+      // If the `--debug` flag was used above instead of `--template` then
+      // there's a good change additional output was included which is not
+      // relevant to the information we want. It should be safe to call this
+      // regardless of whether we used `--debug` or `--template` so there isn't
+      // a need to track which argument was used.
+      $line = DiffusionMercurialCommandEngine::filterMercurialDebugOutput(
+        $line);
+
+      // Just in case new versions of Mercurial add arbitrary output when using
+      // the `--debug`, do a quick sanity check that this line is formatted in
+      // a way we're expecting.
+      if (strpos($line, ':') === false) {
+        phlog(pht('Unexpected output from hg annotate: %s', $line));
+        continue;
+      }
       list($commit) = explode(':', $line, 2);
       $result[] = $commit;
     }
diff --git a/src/applications/diffusion/query/lowlevel/DiffusionLowLevelParentsQuery.php b/src/applications/diffusion/query/lowlevel/DiffusionLowLevelParentsQuery.php
--- a/src/applications/diffusion/query/lowlevel/DiffusionLowLevelParentsQuery.php
+++ b/src/applications/diffusion/query/lowlevel/DiffusionLowLevelParentsQuery.php
@@ -47,23 +47,23 @@
   private function loadMercurialParents() {
     $repository = $this->getRepository();
 
+    $hg_analyzer = PhutilBinaryAnalyzer::getForBinary('hg');
+    if ($hg_analyzer->isMercurialTemplatePnodeAvailable()) {
+      $hg_log_template = '{p1.node} {p2.node}';
+    } else {
+      $hg_log_template = '{p1node} {p2node}';
+    }
+
     list($stdout) = $repository->execxLocalCommand(
-      'log --debug --limit 1 --template={parents} --rev %s',
+      'log --limit 1 --template %s --rev %s',
+      $hg_log_template,
       $this->identifier);
 
-    $stdout = DiffusionMercurialCommandEngine::filterMercurialDebugOutput(
-      $stdout);
-
     $hashes = preg_split('/\s+/', trim($stdout));
     foreach ($hashes as $key => $value) {
-      // Mercurial parents look like "23:ad9f769d6f786fad9f76d9a" -- we want
-      // to strip out the local rev part.
-      list($local, $global) = explode(':', $value);
-      $hashes[$key] = $global;
-
-      // With --debug we get 40-character hashes but also get the "000000..."
-      // hash for missing parents; ignore it.
-      if (preg_match('/^0+$/', $global)) {
+      // We get 40-character hashes but also get the "000000..." hash for
+      // missing parents; ignore it.
+      if (preg_match('/^0+\z/', $value)) {
         unset($hashes[$key]);
       }
     }
diff --git a/src/applications/repository/storage/__tests__/PhabricatorRepositoryTestCase.php b/src/applications/repository/storage/__tests__/PhabricatorRepositoryTestCase.php
--- a/src/applications/repository/storage/__tests__/PhabricatorRepositoryTestCase.php
+++ b/src/applications/repository/storage/__tests__/PhabricatorRepositoryTestCase.php
@@ -100,55 +100,6 @@
 
   }
 
-  public function testFilterMercurialDebugOutput() {
-    $map = array(
-      '' => '',
-
-      "quack\n" => "quack\n",
-
-      "ignoring untrusted configuration option x.y = z\nquack\n" =>
-        "quack\n",
-
-      "ignoring untrusted configuration option x.y = z\n".
-      "ignoring untrusted configuration option x.y = z\n".
-      "quack\n" =>
-        "quack\n",
-
-      "ignoring untrusted configuration option x.y = z\n".
-      "ignoring untrusted configuration option x.y = z\n".
-      "ignoring untrusted configuration option x.y = z\n".
-      "quack\n" =>
-        "quack\n",
-
-      "quack\n".
-      "ignoring untrusted configuration option x.y = z\n".
-      "ignoring untrusted configuration option x.y = z\n".
-      "ignoring untrusted configuration option x.y = z\n" =>
-        "quack\n",
-
-      "ignoring untrusted configuration option x.y = z\n".
-      "ignoring untrusted configuration option x.y = z\n".
-      "duck\n".
-      "ignoring untrusted configuration option x.y = z\n".
-      "ignoring untrusted configuration option x.y = z\n".
-      "bread\n".
-      "ignoring untrusted configuration option x.y = z\n".
-      "quack\n" =>
-        "duck\nbread\nquack\n",
-
-      "ignoring untrusted configuration option x.y = z\n".
-      "duckignoring untrusted configuration option x.y = z\n".
-      "quack" =>
-        'duckquack',
-    );
-
-    foreach ($map as $input => $expect) {
-      $actual = DiffusionMercurialCommandEngine::filterMercurialDebugOutput(
-        $input);
-      $this->assertEqual($expect, $actual, $input);
-    }
-  }
-
   public function testRepositoryShortNameValidation() {
     $good = array(
       'sensible-repository',