diff --git a/src/ai/backend/client/cli/session/lifecycle.py b/src/ai/backend/client/cli/session/lifecycle.py
index a7a053f4bdf..9a6666c925c 100644
--- a/src/ai/backend/client/cli/session/lifecycle.py
+++ b/src/ai/backend/client/cli/session/lifecycle.py
@@ -28,7 +28,6 @@
 from ai.backend.client.cli.types import CLIContext
 from ai.backend.common.arch import DEFAULT_IMAGE_ARCH
 from ai.backend.common.types import ClusterMode
-from ai.backend.common.utils import get_first_timestamp_for_status
 
 from ...compat import asyncio_run
 from ...exceptions import BackendAPIError
@@ -36,6 +35,7 @@
 from ...output.fields import session_fields
 from ...output.types import FieldSpec
 from ...session import AsyncSession, Session
+from ...utils import get_first_timestamp_for_status
 from .. import events
 from ..pretty import (
     ProgressViewer,
diff --git a/src/ai/backend/client/utils.py b/src/ai/backend/client/utils.py
index b95fc5c9b88..6561eacedf8 100644
--- a/src/ai/backend/client/utils.py
+++ b/src/ai/backend/client/utils.py
@@ -1,6 +1,10 @@
+from __future__ import annotations
+
 import io
 import os
+from datetime import datetime
 
+from dateutil.parser import parse as dtparse
 from tqdm import tqdm
 
 
@@ -48,3 +52,13 @@ def readinto1(self, *args, **kwargs):
         count = super().readinto1(*args, **kwargs)
         self.tqdm.set_postfix(file=self._filename, refresh=False)
         self.tqdm.update(count)
+
+
+def get_first_timestamp_for_status(
+    status_history: list[dict[str, str]],
+    status: str,
+) -> datetime | None:
+    for rec in status_history:
+        if rec["status"] == status:
+            return dtparse(rec["timestamp"])
+    return None
diff --git a/src/ai/backend/common/utils.py b/src/ai/backend/common/utils.py
index acadeb48d79..34b74cc684d 100644
--- a/src/ai/backend/common/utils.py
+++ b/src/ai/backend/common/utils.py
@@ -8,7 +8,7 @@
 import sys
 import uuid
 from collections import OrderedDict
-from datetime import datetime, timedelta
+from datetime import timedelta
 from itertools import chain
 from pathlib import Path
 from typing import (
@@ -25,7 +25,6 @@
 
 import aiofiles
 from async_timeout import timeout
-from dateutil.parser import parse as dtparse
 
 if TYPE_CHECKING:
     from decimal import Decimal
@@ -405,16 +404,3 @@ async def umount(
             fstab = Fstab(fp)
             await fstab.remove_by_mountpoint(str(mountpoint))
     return True
-
-
-def get_first_timestamp_for_status(
-    status_history_records: list[dict[str, str]], status: str
-) -> datetime | None:
-    """
-    Get the first occurrence time of the given status from the status history records.
-    """
-
-    for status_history in status_history_records:
-        if status_history["status"] == status:
-            return dtparse(status_history["timestamp"])
-    return None
diff --git a/src/ai/backend/manager/models/kernel.py b/src/ai/backend/manager/models/kernel.py
index 4734a15a1de..2e009127cb6 100644
--- a/src/ai/backend/manager/models/kernel.py
+++ b/src/ai/backend/manager/models/kernel.py
@@ -46,7 +46,6 @@
     SessionTypes,
     VFolderMount,
 )
-from ai.backend.common.utils import get_first_timestamp_for_status
 
 from ..api.exceptions import (
     BackendError,
@@ -83,7 +82,9 @@
     ExtendedAsyncSAEngine,
     JSONCoalesceExpr,
     execute_with_retry,
+    get_first_timestamp_for_status,
     sql_append_dict_to_list,
+    sql_json_merge,
 )
 
 if TYPE_CHECKING:
@@ -927,8 +928,8 @@ def parse_row(cls, ctx: GraphQueryContext, row: KernelRow) -> Mapping[str, Any]:
             hide_agents = False
         else:
             hide_agents = ctx.local_config["manager"]["hide-agents"]
-        status_history = row.status_history
-        scheduled_at = get_first_timestamp_for_status(status_history, KernelStatus.SCHEDULED.name)
+        status_history = cast(list[dict[str, str]], row.status_history)
+        scheduled_at = get_first_timestamp_for_status(status_history, KernelStatus.SCHEDULED)
 
         return {
             # identity
diff --git a/src/ai/backend/manager/models/resource_usage.py b/src/ai/backend/manager/models/resource_usage.py
index 76b33016fe9..0916cadf3c5 100644
--- a/src/ai/backend/manager/models/resource_usage.py
+++ b/src/ai/backend/manager/models/resource_usage.py
@@ -1,8 +1,9 @@
 from __future__ import annotations
 
+import json
 from datetime import datetime
 from enum import Enum
-from typing import Any, Mapping, Optional, Sequence
+from typing import Any, Mapping, Optional, Sequence, cast
 from uuid import UUID
 
 import attrs
@@ -14,14 +15,15 @@
 from sqlalchemy.orm import joinedload, load_only
 
 from ai.backend.common import redis_helper
+from ai.backend.common.json import ExtendedJSONEncoder
 from ai.backend.common.types import RedisConnectionInfo
-from ai.backend.common.utils import get_first_timestamp_for_status, nmget
+from ai.backend.common.utils import nmget
 
 from .group import GroupRow
 from .kernel import LIVE_STATUS, RESOURCE_USAGE_KERNEL_STATUSES, KernelRow, KernelStatus
 from .session import SessionRow
 from .user import UserRow
-from .utils import ExtendedAsyncSAEngine
+from .utils import ExtendedAsyncSAEngine, get_first_timestamp_for_status
 
 __all__: Sequence[str] = (
     "ResourceGroupUnit",
@@ -517,7 +519,9 @@ async def _pipe_builder(r: Redis) -> RedisPipeline:
             created_at=kern.created_at,
             terminated_at=kern.terminated_at,
             scheduled_at=str(
-                get_first_timestamp_for_status(kern.status_history, KernelStatus.SCHEDULED.name)
+                get_first_timestamp_for_status(
+                    cast(list[dict[str, str]], kern.status_history), KernelStatus.SCHEDULED
+                )
             ),
             used_time=kern.used_time,
             used_days=kern.get_used_days(local_tz),
@@ -536,7 +540,7 @@ async def _pipe_builder(r: Redis) -> RedisPipeline:
             images={kern.image},
             agents={kern.agent},
             status=kern.status.name,
-            status_history=kern.status_history,
+            status_history=json.dumps(kern.status_history, cls=ExtendedJSONEncoder),
             cluster_mode=kern.cluster_mode,
             status_info=kern.status_info,
             group_unit=ResourceGroupUnit.KERNEL,
diff --git a/src/ai/backend/manager/models/session.py b/src/ai/backend/manager/models/session.py
index 53ba67a665b..8cbdd06afb9 100644
--- a/src/ai/backend/manager/models/session.py
+++ b/src/ai/backend/manager/models/session.py
@@ -38,7 +38,6 @@
     SessionTypes,
     VFolderMount,
 )
-from ai.backend.common.utils import get_first_timestamp_for_status
 
 from ..api.exceptions import (
     AgentError,
@@ -80,7 +79,9 @@
     JSONCoalesceExpr,
     agg_to_array,
     execute_with_retry,
+    get_first_timestamp_for_status,
     sql_append_dict_to_list,
+    sql_json_merge,
 )
 
 if TYPE_CHECKING:
@@ -1324,9 +1325,7 @@ def parse_row(cls, ctx: GraphQueryContext, row: Row) -> Mapping[str, Any]:
         full_name = getattr(row, "full_name")
         group_name = getattr(row, "group_name")
         row = row.SessionRow
-        scheduled_at = get_first_timestamp_for_status(
-            row.status_history, SessionStatus.SCHEDULED.name
-        )
+        scheduled_at = get_first_timestamp_for_status(row.status_history, SessionStatus.SCHEDULED)
 
         return {
             # identity
diff --git a/src/ai/backend/manager/models/utils.py b/src/ai/backend/manager/models/utils.py
index 7093ac876cc..77565762639 100644
--- a/src/ai/backend/manager/models/utils.py
+++ b/src/ai/backend/manager/models/utils.py
@@ -6,6 +6,7 @@
 import logging
 from contextlib import AbstractAsyncContextManager as AbstractAsyncCtxMgr
 from contextlib import asynccontextmanager as actxmgr
+from datetime import datetime
 from typing import (
     TYPE_CHECKING,
     Any,
@@ -23,6 +24,7 @@
 from urllib.parse import quote_plus as urlquote
 
 import sqlalchemy as sa
+from dateutil.parser import parse as dtparse
 from sqlalchemy.dialects import postgresql as psql
 from sqlalchemy.engine import create_engine as _create_engine
 from sqlalchemy.exc import DBAPIError
@@ -44,6 +46,10 @@
 
 if TYPE_CHECKING:
     from ..config import LocalConfig
+    from . import (
+        KernelStatus,
+        SessionStatus,
+    )
 
 from ..defs import LockID
 from ..types import Sentinel
@@ -536,3 +542,17 @@ async def vacuum_db(
             vacuum_sql = "VACUUM FULL" if vacuum_full else "VACUUM"
             log.info(f"Perfoming {vacuum_sql} operation...")
             await conn.exec_driver_sql(vacuum_sql)
+
+
+def get_first_timestamp_for_status(
+    status_history_records: list[dict[str, str]],
+    status: KernelStatus | SessionStatus,
+) -> datetime | None:
+    """
+    Get the first occurrence time of the given status from the status history records.
+    """
+
+    for status_history in status_history_records:
+        if status_history["status"] == status.name:
+            return dtparse(status_history["timestamp"])
+    return None
diff --git a/src/ai/backend/manager/utils.py b/src/ai/backend/manager/utils.py
index 091b9a767cb..8a4c070a9bf 100644
--- a/src/ai/backend/manager/utils.py
+++ b/src/ai/backend/manager/utils.py
@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 from typing import Optional
 from uuid import UUID