diff --git a/Dockerfile b/Dockerfile
index 1db9c23d..d2f1d237 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -30,6 +30,9 @@ RUN --mount=type=cache,sharing=locked,target=/var/cache/apt-run apt-get update \
         gettext-base
 RUN busybox --install
 
+# postgresql and redis cli are not required, but install for development convenience
+RUN --mount=type=cache,sharing=locked,target=/var/cache/apt-run apt-get install -y --no-install-recommends postgresql-client redis-tools
+
 COPY . /neodb
 WORKDIR /neodb
 COPY --from=build /neodb-venv /neodb-venv
diff --git a/catalog/templates/_item_comments.html b/catalog/templates/_item_comments.html
index 706e3a0e..07dc3622 100644
--- a/catalog/templates/_item_comments.html
+++ b/catalog/templates/_item_comments.html
@@ -46,10 +46,10 @@
                data-uuid="{{ comment.item.uuid }}"><i class="fa-regular fa-circle-play"></i></a>
           </span>
         {% endif %}
-        {% if comment.post %}
-          {% include "action_reply_post.html" with post=comment.post %}
-          {% include "action_like_post.html" with post=comment.post %}
-          {% include "action_open_post.html" with post=comment.post %}
+        {% if comment.latest_post %}
+          {% include "action_reply_piece.html" with post=comment.latest_post piece=comment %}
+          {% include "action_like_post.html" with post=comment.latest_post %}
+          {% include "action_open_post.html" with post=comment.latest_post %}
         {% endif %}
       </span>
       <span>
@@ -66,7 +66,7 @@
       </span>
       {% if comment.item != item %}<a href="{{ comment.item_url }}">{{ comment.item.title }}</a>{% endif %}
       <div>{{ comment.html|safe }}</div>
-      {% if comment.post_id %}<div id="replies_{{ comment.post_id }}"></div>{% endif %}
+      {% if comment.latest_post %}<div id="replies_{{ comment.latest_post.pk }}"></div>{% endif %}
     </section>
   {% else %}
     <a hx-get="{% url 'catalog:comments' comment.item.url_path comment.item.uuid %}?last={{ comment.created_time|date:'Y-m-d H:i:s.uO'|urlencode }}"
diff --git a/journal/migrations/0016_piecepost_piece_posts_piecepost_unique_piece_post.py b/journal/migrations/0016_piecepost_piece_posts_piecepost_unique_piece_post.py
new file mode 100644
index 00000000..50ab1043
--- /dev/null
+++ b/journal/migrations/0016_piecepost_piece_posts_piecepost_unique_piece_post.py
@@ -0,0 +1,56 @@
+# Generated by Django 4.2.4 on 2023-08-25 18:50
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("takahe", "0001_initial"),
+        ("journal", "0015_use_identity_support_remote_piece"),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name="PiecePost",
+            fields=[
+                (
+                    "id",
+                    models.BigAutoField(
+                        auto_created=True,
+                        primary_key=True,
+                        serialize=False,
+                        verbose_name="ID",
+                    ),
+                ),
+                (
+                    "piece",
+                    models.ForeignKey(
+                        on_delete=django.db.models.deletion.CASCADE, to="journal.piece"
+                    ),
+                ),
+                (
+                    "post",
+                    models.ForeignKey(
+                        db_constraint=False,
+                        on_delete=django.db.models.deletion.CASCADE,
+                        to="takahe.post",
+                    ),
+                ),
+            ],
+        ),
+        migrations.AddField(
+            model_name="piece",
+            name="posts",
+            field=models.ManyToManyField(
+                related_name="pieces", through="journal.PiecePost", to="takahe.post"
+            ),
+        ),
+        migrations.AddConstraint(
+            model_name="piecepost",
+            constraint=models.UniqueConstraint(
+                fields=("piece", "post"), name="unique_piece_post"
+            ),
+        ),
+    ]
diff --git a/journal/migrations/0017_alter_piece_options_and_more.py b/journal/migrations/0017_alter_piece_options_and_more.py
new file mode 100644
index 00000000..b9411324
--- /dev/null
+++ b/journal/migrations/0017_alter_piece_options_and_more.py
@@ -0,0 +1,25 @@
+# Generated by Django 4.2.4 on 2023-08-26 00:59
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("journal", "0016_piecepost_piece_posts_piecepost_unique_piece_post"),
+    ]
+
+    operations = [
+        migrations.AlterModelOptions(
+            name="piece",
+            options={"base_manager_name": "objects"},
+        ),
+        migrations.RemoveIndex(
+            model_name="piece",
+            name="journal_pie_post_id_6a74ff_idx",
+        ),
+        migrations.RemoveField(
+            model_name="piece",
+            name="post_id",
+        ),
+    ]
diff --git a/journal/models/comment.py b/journal/models/comment.py
index dc566dee..2af04e22 100644
--- a/journal/models/comment.py
+++ b/journal/models/comment.py
@@ -38,12 +38,12 @@ class Comment(Content):
             "text": content,
             "local": False,
             "remote_id": obj["id"],
-            "post_id": post_id,
             "visibility": visibility,
             "created_time": datetime.fromisoformat(obj["published"]),
             "edited_time": datetime.fromisoformat(obj["updated"]),
         }
         p, _ = cls.objects.update_or_create(owner=owner, item=item, defaults=d)
+        p.link_post_id(post_id)
         return p
 
     @property
diff --git a/journal/models/common.py b/journal/models/common.py
index 3c694394..f48f5575 100644
--- a/journal/models/common.py
+++ b/journal/models/common.py
@@ -1,5 +1,7 @@
 import re
 import uuid
+from functools import cached_property
+from typing import TYPE_CHECKING
 
 from django.conf import settings
 from django.db import connection, models
@@ -10,13 +12,14 @@ from django.utils.translation import gettext_lazy as _
 from polymorphic.models import PolymorphicModel
 
 from catalog.common.models import AvailableItemCategory, Item, ItemCategory
-from catalog.models import *
+from catalog.models import item_categories, item_content_types
 from takahe.utils import Takahe
 from users.models import APIdentity, User
 
 from .mixins import UserOwnedObjectMixin
 
-_logger = logging.getLogger(__name__)
+if TYPE_CHECKING:
+    from takahe.models import Post
 
 
 class VisibilityType(models.IntegerChoices):
@@ -117,12 +120,9 @@ class Piece(PolymorphicModel, UserOwnedObjectMixin):
     url_path = "p"  # subclass must specify this
     uid = models.UUIDField(default=uuid.uuid4, editable=False, db_index=True)
     local = models.BooleanField(default=True)
-    post_id = models.BigIntegerField(null=True, default=None)
-
-    class Meta:
-        indexes = [
-            models.Index(fields=["post_id"]),
-        ]
+    posts = models.ManyToManyField(
+        "takahe.Post", related_name="pieces", through="PiecePost"
+    )
 
     @property
     def uuid(self):
@@ -140,32 +140,32 @@ class Piece(PolymorphicModel, UserOwnedObjectMixin):
     def api_url(self):
         return f"/api/{self.url}" if self.url_path else None
 
-    @property
-    def post(self):
-        return Takahe.get_post(self.post_id) if self.post_id else None
-
     @property
     def shared_link(self):
-        return Takahe.get_post_url(self.post_id) if self.post_id else None
+        return Takahe.get_post_url(self.latest_post.pk) if self.latest_post else None
 
     @property
     def like_count(self):
         return (
-            Takahe.get_post_stats(self.post_id).get("likes", 0) if self.post_id else 0
+            Takahe.get_post_stats(self.latest_post.pk).get("likes", 0)
+            if self.latest_post
+            else 0
         )
 
     def is_liked_by(self, user):
-        return self.post_id and Takahe.post_liked_by(self.post_id, user)
+        return self.latest_post and Takahe.post_liked_by(self.latest_post.pk, user)
 
     @property
     def reply_count(self):
         return (
-            Takahe.get_post_stats(self.post_id).get("replies", 0) if self.post_id else 0
+            Takahe.get_post_stats(self.latest_post.pk).get("replies", 0)
+            if self.latest_post
+            else 0
         )
 
     def get_replies(self, viewing_identity):
-        return Takahe.get_post_replies(
-            self.post_id, viewing_identity.pk if viewing_identity else None
+        return Takahe.get_replies_for_posts(
+            self.all_post_ids, viewing_identity.pk if viewing_identity else None
         )
 
     @classmethod
@@ -189,6 +189,37 @@ class Piece(PolymorphicModel, UserOwnedObjectMixin):
     def ap_object(self):
         raise NotImplemented
 
+    def link_post_id(self, post_id: int):
+        PiecePost.objects.get_or_create(piece=self, post_id=post_id)
+
+    def link_post(self, post: "Post"):
+        return self.link_post_id(post.pk)
+
+    @cached_property
+    def latest_post(self):
+        # local post id is ordered by their created time
+        pp = PiecePost.objects.filter(piece=self).order_by("-post_id").first()
+        return Takahe.get_post(pp.post_id) if pp else None  # type: ignore
+
+    @cached_property
+    def all_post_ids(self):
+        post_ids = list(
+            PiecePost.objects.filter(piece=self).values_list("post_id", flat=True)
+        )
+        return post_ids
+
+
+class PiecePost(models.Model):
+    piece = models.ForeignKey(Piece, on_delete=models.CASCADE)
+    post = models.ForeignKey(
+        "takahe.Post", db_constraint=False, db_index=True, on_delete=models.CASCADE
+    )
+
+    class Meta:
+        constraints = [
+            models.UniqueConstraint(fields=["piece", "post"], name="unique_piece_post"),
+        ]
+
 
 class Content(Piece):
     owner = models.ForeignKey(APIdentity, on_delete=models.PROTECT)
diff --git a/journal/models/mark.py b/journal/models/mark.py
index 48499f5a..3657efc5 100644
--- a/journal/models/mark.py
+++ b/journal/models/mark.py
@@ -20,7 +20,6 @@ from catalog.collection.models import Collection as CatalogCollection
 from catalog.common import jsondata
 from catalog.common.models import Item, ItemCategory
 from catalog.common.utils import DEFAULT_ITEM_COVER, piece_cover_path
-from catalog.models import *
 from mastodon.api import boost_toot
 from takahe.utils import Takahe
 from users.models import APIdentity
@@ -137,7 +136,8 @@ class Mark:
             or visibility != self.visibility
         )
         if shelf_type is None or visibility != self.visibility:
-            Takahe.delete_mark(self)
+            if self.shelfmember:
+                Takahe.delete_posts(self.shelfmember.all_post_ids)
         if created_time and created_time >= timezone.now():
             created_time = None
         post_as_new = shelf_type != self.shelf_type or visibility != self.visibility
diff --git a/journal/models/rating.py b/journal/models/rating.py
index b9034ab2..80479c93 100644
--- a/journal/models/rating.py
+++ b/journal/models/rating.py
@@ -59,12 +59,12 @@ class Rating(Content):
             "grade": value,
             "local": False,
             "remote_id": obj["id"],
-            "post_id": post_id,
             "visibility": visibility,
             "created_time": datetime.fromisoformat(obj["published"]),
             "edited_time": datetime.fromisoformat(obj["updated"]),
         }
         p, _ = cls.objects.update_or_create(owner=owner, item=item, defaults=d)
+        p.link_post_id(post_id)
         return p
 
     @staticmethod
diff --git a/journal/models/shelf.py b/journal/models/shelf.py
index d7b28852..8f9352ab 100644
--- a/journal/models/shelf.py
+++ b/journal/models/shelf.py
@@ -92,12 +92,12 @@ class ShelfMember(ListMember):
             "position": 0,
             "local": False,
             # "remote_id": obj["id"],
-            "post_id": post_id,
             "visibility": visibility,
             "created_time": datetime.fromisoformat(obj["published"]),
             "edited_time": datetime.fromisoformat(obj["updated"]),
         }
         p, _ = cls.objects.update_or_create(owner=owner, item=item, defaults=d)
+        p.link_post_id(post_id)
         return p
 
     @cached_property
@@ -277,12 +277,11 @@ class ShelfManager:
 
     @classmethod
     def get_action_label(
-        cls, shelf_type: ShelfType, item_category: ItemCategory
+        cls, shelf_type: ShelfType | str, item_category: ItemCategory
     ) -> str:
-        sts = [
-            n[2] for n in ShelfTypeNames if n[0] == item_category and n[1] == shelf_type
-        ]
-        return sts[0] if sts else str(shelf_type)
+        st = str(shelf_type)
+        sts = [n[2] for n in ShelfTypeNames if n[0] == item_category and n[1] == st]
+        return sts[0] if sts else st
 
     @classmethod
     def get_label(cls, shelf_type: ShelfType, item_category: ItemCategory):
diff --git a/journal/templates/action_reply_piece.html b/journal/templates/action_reply_piece.html
new file mode 100644
index 00000000..3d3a22ea
--- /dev/null
+++ b/journal/templates/action_reply_piece.html
@@ -0,0 +1,9 @@
+<span>
+  <a hx-get="{% url 'journal:piece_replies' piece.uuid %}"
+     hx-swap="outerHTML"
+     hx-trigger="click once"
+     hx-target="#replies_{{ post.pk }}">
+    <i class="fa-solid fa-reply"></i>
+    {% if post.stats.replies %}<span>{{ post.stats.replies }}</span>{% endif %}
+  </a>
+</span>
diff --git a/journal/templatetags/user_actions.py b/journal/templatetags/user_actions.py
index 528a553b..d0d33a89 100644
--- a/journal/templatetags/user_actions.py
+++ b/journal/templatetags/user_actions.py
@@ -23,9 +23,9 @@ def wish_item_action(context, item):
 def like_piece_action(context, piece):
     user = context["request"].user
     action = {}
-    if user and user.is_authenticated and piece and piece.post_id:
+    if user and user.is_authenticated and piece and piece.latest_post:
         action = {
-            "taken": Takahe.post_liked_by(piece.post_id, user),
+            "taken": Takahe.post_liked_by(piece.latest_post.pk, user),
             "url": reverse("journal:like", args=[piece.uuid]),
         }
     return action
diff --git a/journal/views/mark.py b/journal/views/mark.py
index 1e24269c..e30d89c9 100644
--- a/journal/views/mark.py
+++ b/journal/views/mark.py
@@ -51,8 +51,9 @@ def like(request: AuthedHttpRequest, piece_uuid):
     piece = get_object_or_404(Piece, uid=get_uuid_or_404(piece_uuid))
     if not piece:
         raise Http404()
-    if piece.post_id:
-        Takahe.like_post(piece.post_id, request.user.identity.pk)
+    post = piece.latest_post
+    if post:
+        Takahe.like_post(post.pk, request.user.identity.pk)
     if request.GET.get("back"):
         return HttpResponseRedirect(request.META.get("HTTP_REFERER", "/"))
     elif request.GET.get("stats"):
@@ -76,8 +77,9 @@ def unlike(request: AuthedHttpRequest, piece_uuid):
     piece = get_object_or_404(Piece, uid=get_uuid_or_404(piece_uuid))
     if not piece:
         raise Http404()
-    if piece.post_id:
-        Takahe.unlike_post(piece.post_id, request.user.identity.pk)
+    post = piece.latest_post
+    if post:
+        Takahe.unlike_post(post.pk, request.user.identity.pk)
     if request.GET.get("back"):
         return HttpResponseRedirect(request.META.get("HTTP_REFERER", "/"))
     elif request.GET.get("stats"):
diff --git a/journal/views/post.py b/journal/views/post.py
index 96779d7b..cc10e615 100644
--- a/journal/views/post.py
+++ b/journal/views/post.py
@@ -4,7 +4,6 @@ from django.shortcuts import get_object_or_404, redirect, render
 from django.urls import reverse
 from django.utils.translation import gettext_lazy as _
 
-from catalog.models import *
 from common.utils import (
     AuthedHttpRequest,
     PageLinksGenerator,
@@ -23,12 +22,14 @@ def piece_replies(request: AuthedHttpRequest, piece_uuid: str):
     if not piece.is_visible_to(request.user):
         raise PermissionDenied()
     replies = piece.get_replies(request.user.identity)
-    return render(request, "replies.html", {"post": piece.post, "replies": replies})
+    return render(
+        request, "replies.html", {"post": piece.latest_post, "replies": replies}
+    )
 
 
 @login_required
 def post_replies(request: AuthedHttpRequest, post_id: int):
-    replies = Takahe.get_post_replies(post_id, request.user.identity.pk)
+    replies = Takahe.get_replies_for_posts([post_id], request.user.identity.pk)
     return render(
         request, "replies.html", {"post": Takahe.get_post(post_id), "replies": replies}
     )
@@ -41,7 +42,7 @@ def post_reply(request: AuthedHttpRequest, post_id: int):
     if request.method != "POST" or not content:
         raise BadRequest()
     Takahe.reply_post(post_id, request.user.identity.pk, content, visibility)
-    replies = Takahe.get_post_replies(post_id, request.user.identity.pk)
+    replies = Takahe.get_replies_for_posts([post_id], request.user.identity.pk)
     return render(
         request, "replies.html", {"post": Takahe.get_post(post_id), "replies": replies}
     )
diff --git a/takahe/ap_handlers.py b/takahe/ap_handlers.py
index 5fdc87f1..3c9ce8cd 100644
--- a/takahe/ap_handlers.py
+++ b/takahe/ap_handlers.py
@@ -97,7 +97,7 @@ def post_updated(pk, obj):
 
 
 def post_deleted(pk, obj):
-    Piece.objects.filter(post_id=pk, local=False).delete()
+    Piece.objects.filter(posts__id=pk, local=False).delete()
 
 
 def user_follow_updated(source_identity_pk, target_identity_pk):
diff --git a/takahe/utils.py b/takahe/utils.py
index 8048167d..a0931ced 100644
--- a/takahe/utils.py
+++ b/takahe/utils.py
@@ -377,18 +377,21 @@ class Takahe:
         return post
 
     @staticmethod
-    def get_post(post_pk: int) -> str | None:
+    def get_post(post_pk: int) -> Post | None:
         return Post.objects.filter(pk=post_pk).first()
 
+    @staticmethod
+    def get_posts(post_pks: list[int]):
+        return Post.objects.filter(pk__in=post_pks)
+
     @staticmethod
     def get_post_url(post_pk: int) -> str | None:
         post = Post.objects.filter(pk=post_pk).first() if post_pk else None
         return post.object_uri if post else None
 
     @staticmethod
-    def delete_mark(mark):
-        if mark.shelfmember and mark.shelfmember.post_id:
-            Post.objects.filter(pk=mark.shelfmember.post_id).update(state="deleted")
+    def delete_posts(post_pks):
+        Post.objects.filter(pk__in=post_pks).update(state="deleted")
 
     @staticmethod
     def post_mark(mark, share_as_new_post: bool) -> Post | None:
@@ -428,26 +431,21 @@ class Takahe:
             v = Takahe.Visibilities.public
         else:
             v = Takahe.Visibilities.unlisted
+        existing_post = None if share_as_new_post else mark.shelfmember.latest_post
         post = Takahe.post(
             mark.owner.pk,
             pre_conetent,
             content,
             v,
             data,
-            None if share_as_new_post else mark.shelfmember.post_id,
+            existing_post.pk if existing_post else None,
             mark.shelfmember.created_time,
         )
         if not post:
             return
-        if post.pk != mark.shelfmember.post_id:
-            mark.shelfmember.post_id = post.pk
-            mark.shelfmember.save(update_fields=["post_id"])
-        if mark.comment and post.pk != mark.comment.post_id:
-            mark.comment.post_id = post.pk
-            mark.comment.save(update_fields=["post_id"])
-        if mark.rating and post.pk != mark.rating.post_id:
-            mark.rating.post_id = post.pk
-            mark.rating.save(update_fields=["post_id"])
+        for piece in [mark.shelfmember, mark.comment, mark.rating]:
+            if piece:
+                piece.link_post(post)
         return post
 
     @staticmethod
@@ -522,11 +520,11 @@ class Takahe:
         return post.stats or {}
 
     @staticmethod
-    def get_post_replies(post_pk: int | None, identity_pk: int | None):
-        if not post_pk:
-            return Post.objects.none()
-        node = Post.objects.filter(pk=post_pk).first()
-        if not node:
+    def get_replies_for_posts(post_pks: list[int], identity_pk: int | None):
+        post_uris = Post.objects.filter(pk__in=post_pks).values_list(
+            "object_uri", flat=True
+        )
+        if not post_uris.exists():
             return Post.objects.none()
         identity = (
             Identity.objects.filter(pk=identity_pk).first() if identity_pk else None
@@ -542,7 +540,7 @@ class Takahe:
                 "author",
                 "author__domain",
             )
-            .filter(in_reply_to=node.object_uri)
+            .filter(in_reply_to__in=post_uris)
             .order_by("published")
         )
         if identity: