diff --git a/wcfsetup/install/files/acp/database/update_com.woltlab.wcf_6.3_step1.php b/wcfsetup/install/files/acp/database/update_com.woltlab.wcf_6.3_step1.php
index 09e41d6dcb0..bddd2c5e6f7 100644
--- a/wcfsetup/install/files/acp/database/update_com.woltlab.wcf_6.3_step1.php
+++ b/wcfsetup/install/files/acp/database/update_com.woltlab.wcf_6.3_step1.php
@@ -8,6 +8,7 @@
  * @license   GNU Lesser General Public License <http://opensource.org/licenses/lgpl-license.php>
  */
 
+use wcf\system\database\table\column\BinaryDatabaseTableColumn;
 use wcf\system\database\table\column\CharDatabaseTableColumn;
 use wcf\system\database\table\column\DefaultFalseBooleanDatabaseTableColumn;
 use wcf\system\database\table\column\IntDatabaseTableColumn;
@@ -75,8 +76,23 @@
         ]),
     PartialDatabaseTable::create('wcf1_acp_session_log')
         ->columns([
+            BinaryDatabaseTableColumn::create('sessionID')
+                ->notNull()
+                ->length(40),
             NotNullVarchar255DatabaseTableColumn::create('hostname')
                 ->defaultValue('')
                 ->drop(),
         ]),
+    PartialDatabaseTable::create('wcf1_session')
+        ->columns([
+            BinaryDatabaseTableColumn::create('sessionID')
+                ->notNull()
+                ->length(40),
+        ]),
+    PartialDatabaseTable::create('wcf1_user_session')
+        ->columns([
+            BinaryDatabaseTableColumn::create('sessionID')
+                ->notNull()
+                ->length(40),
+        ]),
 ];
diff --git a/wcfsetup/install/files/lib/system/package/PackageInstallationDispatcher.class.php b/wcfsetup/install/files/lib/system/package/PackageInstallationDispatcher.class.php
index 57807398a03..1781485b8b9 100644
--- a/wcfsetup/install/files/lib/system/package/PackageInstallationDispatcher.class.php
+++ b/wcfsetup/install/files/lib/system/package/PackageInstallationDispatcher.class.php
@@ -2,7 +2,6 @@
 
 namespace wcf\system\package;
 
-use ParagonIE\ConstantTime\Hex;
 use wcf\data\application\Application;
 use wcf\data\application\ApplicationBuilder;
 use wcf\data\devtools\project\DevtoolsProjectAction;
@@ -257,9 +256,9 @@ protected function finalizeWcfSetup(): void
             'user_session',
             CryptoUtil::createSignedString(
                 \pack(
-                    'CA20C',
-                    1,
-                    Hex::decode(WCF::getSession()->sessionID),
+                    'Ca40C',
+                    2,
+                    WCF::getSession()->sessionID,
                     0
                 )
             )
diff --git a/wcfsetup/install/files/lib/system/session/SessionHandler.class.php b/wcfsetup/install/files/lib/system/session/SessionHandler.class.php
index a8165e6b540..0ac288a471c 100644
--- a/wcfsetup/install/files/lib/system/session/SessionHandler.class.php
+++ b/wcfsetup/install/files/lib/system/session/SessionHandler.class.php
@@ -2,6 +2,7 @@
 
 namespace wcf\system\session;
 
+use ParagonIE\ConstantTime\Base32;
 use ParagonIE\ConstantTime\Hex;
 use wcf\data\session\Session as LegacySession;
 use wcf\data\session\SessionEditor;
@@ -194,6 +195,19 @@ private function parseCookie(string $value): array
 
                 return $data;
 
+            case 2:
+                if ($length !== 42) {
+                    throw new \InvalidArgumentException(\sprintf(
+                        'Expected exactly 42 Bytes, %d given.',
+                        $length
+                    ));
+                }
+                $data = \unpack('Cversion/a40sessionId/Ctimestep', $value);
+                \assert($data['version'] === 2);
+                \assert(\strlen($data['sessionId']) === 40);
+
+                return $data;
+
             default:
                 throw new \InvalidArgumentException(\sprintf(
                     'Unknown version %d',
@@ -275,9 +289,9 @@ private function getCookieValue(): string
         }
 
         return CryptoUtil::createSignedString(\pack(
-            'CA20C',
-            1,
-            Hex::decode($this->sessionID),
+            'Ca40C',
+            2,
+            $this->sessionID,
             $this->getCookieTimestep()
         ));
     }
@@ -637,7 +651,7 @@ private function getExistingSession(string $sessionID): bool
      */
     private function create(): void
     {
-        $this->sessionID = Hex::encode(\random_bytes(20));
+        $this->sessionID = $this->generateSessionID();
 
         $variables = [
             'frontend' => [],
@@ -692,6 +706,25 @@ private function create(): void
         );
     }
 
+    /**
+     * Generates a session ID that starts with its creation time, keeping inserts into
+     * the primary key of `wcf1_user_session` close to sequential.
+     *
+     * Format: 4 bytes of seconds and 1 byte of 1/256 second steps as Base16, followed by
+     * 17 random bytes (136 bits) as Base32 and the format version `V2`.
+     */
+    private function generateSessionID(): string
+    {
+        // Both parts must come from the same clock reading, `TIME_NOW` is fixed at
+        // the start of the request and would break the ordering within a second.
+        $now = \microtime(true);
+        $seconds = (int)$now;
+
+        return Hex::encode(\pack('NC', $seconds, (int)(($now - $seconds) * 256)))
+            . \substr(Base32::encode(\random_bytes(17)), 0, 28)
+            . 'V2';
+    }
+
     /**
      * Returns the existing legacy session that is shared by all guest sessions of the given spider.
      */
diff --git a/wcfsetup/setup/db/install_com.woltlab.wcf.php b/wcfsetup/setup/db/install_com.woltlab.wcf.php
index 6ed39a027a8..e286eda0908 100644
--- a/wcfsetup/setup/db/install_com.woltlab.wcf.php
+++ b/wcfsetup/setup/db/install_com.woltlab.wcf.php
@@ -307,10 +307,9 @@
     DatabaseTable::create('wcf1_acp_session_log')
         ->columns([
             ObjectIdDatabaseTableColumn::create('sessionLogID'),
-            CharDatabaseTableColumn::create('sessionID')
+            BinaryDatabaseTableColumn::create('sessionID')
                 ->notNull()
-                ->length(40)
-                ->defaultValue(''),
+                ->length(40),
             IntDatabaseTableColumn::create('userID'),
             VarcharDatabaseTableColumn::create('ipAddress')
                 ->notNull()
@@ -3216,7 +3215,7 @@
         ]),
     DatabaseTable::create('wcf1_session')
         ->columns([
-            CharDatabaseTableColumn::create('sessionID')
+            BinaryDatabaseTableColumn::create('sessionID')
                 ->notNull()
                 ->length(40),
             IntDatabaseTableColumn::create('userID'),
@@ -4777,7 +4776,7 @@
         ]),
     DatabaseTable::create('wcf1_user_session')
         ->columns([
-            CharDatabaseTableColumn::create('sessionID')
+            BinaryDatabaseTableColumn::create('sessionID')
                 ->notNull()
                 ->length(40),
             IntDatabaseTableColumn::create('userID'),