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diff --git a/lib/pleroma/migrators/hashtags_table_migrator.ex b/lib/pleroma/migrators/hashtags_table_migrator.ex
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+++ b/lib/pleroma/migrators/hashtags_table_migrator.ex
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+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2021 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Migrators.HashtagsTableMigrator do
+  defmodule State do
+    use Pleroma.Migrators.Support.BaseMigratorState
+
+    @impl Pleroma.Migrators.Support.BaseMigratorState
+    defdelegate data_migration(), to: Pleroma.DataMigration, as: :populate_hashtags_table
+  end
+
+  use Pleroma.Migrators.Support.BaseMigrator
+
+  alias Pleroma.Hashtag
+  alias Pleroma.Migrators.Support.BaseMigrator
+  alias Pleroma.Object
+
+  @impl BaseMigrator
+  def feature_config_path, do: [:features, :improved_hashtag_timeline]
+
+  @impl BaseMigrator
+  def fault_rate_allowance, do: Config.get([:populate_hashtags_table, :fault_rate_allowance], 0)
+
+  @impl BaseMigrator
+  def perform do
+    data_migration_id = data_migration_id()
+    max_processed_id = get_stat(:max_processed_id, 0)
+
+    Logger.info("Transferring embedded hashtags to `hashtags` (from oid: #{max_processed_id})...")
+
+    query()
+    |> where([object], object.id > ^max_processed_id)
+    |> Repo.chunk_stream(100, :batches, timeout: :infinity)
+    |> Stream.each(fn objects ->
+      object_ids = Enum.map(objects, & &1.id)
+
+      results = Enum.map(objects, &transfer_object_hashtags(&1))
+
+      failed_ids =
+        results
+        |> Enum.filter(&(elem(&1, 0) == :error))
+        |> Enum.map(&elem(&1, 1))
+
+      # Count of objects with hashtags: `{:noop, id}` is returned for objects having other AS2 tags
+      chunk_affected_count =
+        results
+        |> Enum.filter(&(elem(&1, 0) == :ok))
+        |> length()
+
+      for failed_id <- failed_ids do
+        _ =
+          Repo.query(
+            "INSERT INTO data_migration_failed_ids(data_migration_id, record_id) " <>
+              "VALUES ($1, $2) ON CONFLICT DO NOTHING;",
+            [data_migration_id, failed_id]
+          )
+      end
+
+      _ =
+        Repo.query(
+          "DELETE FROM data_migration_failed_ids " <>
+            "WHERE data_migration_id = $1 AND record_id = ANY($2)",
+          [data_migration_id, object_ids -- failed_ids]
+        )
+
+      max_object_id = Enum.at(object_ids, -1)
+
+      put_stat(:max_processed_id, max_object_id)
+      increment_stat(:iteration_processed_count, length(object_ids))
+      increment_stat(:processed_count, length(object_ids))
+      increment_stat(:failed_count, length(failed_ids))
+      increment_stat(:affected_count, chunk_affected_count)
+      put_stat(:records_per_second, records_per_second())
+      persist_state()
+
+      # A quick and dirty approach to controlling the load this background migration imposes
+      sleep_interval = Config.get([:populate_hashtags_table, :sleep_interval_ms], 0)
+      Process.sleep(sleep_interval)
+    end)
+    |> Stream.run()
+  end
+
+  @impl BaseMigrator
+  def query do
+    # Note: most objects have Mention-type AS2 tags and no hashtags (but we can't filter them out)
+    # Note: not checking activity type, expecting remove_non_create_objects_hashtags/_ to clean up
+    from(
+      object in Object,
+      where:
+        fragment("(?)->'tag' IS NOT NULL AND (?)->'tag' != '[]'::jsonb", object.data, object.data),
+      select: %{
+        id: object.id,
+        tag: fragment("(?)->'tag'", object.data)
+      }
+    )
+    |> join(:left, [o], hashtags_objects in fragment("SELECT object_id FROM hashtags_objects"),
+      on: hashtags_objects.object_id == o.id
+    )
+    |> where([_o, hashtags_objects], is_nil(hashtags_objects.object_id))
+  end
+
+  @spec transfer_object_hashtags(Map.t()) :: {:noop | :ok | :error, integer()}
+  defp transfer_object_hashtags(object) do
+    embedded_tags = if Map.has_key?(object, :tag), do: object.tag, else: object.data["tag"]
+    hashtags = Object.object_data_hashtags(%{"tag" => embedded_tags})
+
+    if Enum.any?(hashtags) do
+      transfer_object_hashtags(object, hashtags)
+    else
+      {:noop, object.id}
+    end
+  end
+
+  defp transfer_object_hashtags(object, hashtags) do
+    Repo.transaction(fn ->
+      with {:ok, hashtag_records} <- Hashtag.get_or_create_by_names(hashtags) do
+        maps = Enum.map(hashtag_records, &%{hashtag_id: &1.id, object_id: object.id})
+        base_error = "ERROR when inserting hashtags_objects for object with id #{object.id}"
+
+        try do
+          with {rows_count, _} when is_integer(rows_count) <-
+                 Repo.insert_all("hashtags_objects", maps, on_conflict: :nothing) do
+            object.id
+          else
+            e ->
+              Logger.error("#{base_error}: #{inspect(e)}")
+              Repo.rollback(object.id)
+          end
+        rescue
+          e ->
+            Logger.error("#{base_error}: #{inspect(e)}")
+            Repo.rollback(object.id)
+        end
+      else
+        e ->
+          error = "ERROR: could not create hashtags for object #{object.id}: #{inspect(e)}"
+          Logger.error(error)
+          Repo.rollback(object.id)
+      end
+    end)
+  end
+
+  @impl BaseMigrator
+  def retry_failed do
+    data_migration_id = data_migration_id()
+
+    failed_objects_query()
+    |> Repo.chunk_stream(100, :one)
+    |> Stream.each(fn object ->
+      with {res, _} when res != :error <- transfer_object_hashtags(object) do
+        _ =
+          Repo.query(
+            "DELETE FROM data_migration_failed_ids " <>
+              "WHERE data_migration_id = $1 AND record_id = $2",
+            [data_migration_id, object.id]
+          )
+      end
+    end)
+    |> Stream.run()
+
+    put_stat(:failed_count, failures_count())
+    persist_state()
+
+    force_continue()
+  end
+
+  defp failed_objects_query do
+    from(o in Object)
+    |> join(:inner, [o], dmf in fragment("SELECT * FROM data_migration_failed_ids"),
+      on: dmf.record_id == o.id
+    )
+    |> where([_o, dmf], dmf.data_migration_id == ^data_migration_id())
+    |> order_by([o], asc: o.id)
+  end
+
+  @doc """
+  Service func to delete `hashtags_objects` for legacy objects not associated with Create activity.
+  Also deletes unreferenced `hashtags` records (might occur after deletion of `hashtags_objects`).
+  """
+  def delete_non_create_activities_hashtags do
+    hashtags_objects_cleanup_query = """
+    DELETE FROM hashtags_objects WHERE object_id IN
+      (SELECT DISTINCT objects.id FROM objects
+        JOIN hashtags_objects ON hashtags_objects.object_id = objects.id LEFT JOIN activities
+          ON COALESCE(activities.data->'object'->>'id', activities.data->>'object') =
+            (objects.data->>'id')
+          AND activities.data->>'type' = 'Create'
+        WHERE activities.id IS NULL);
+    """
+
+    hashtags_cleanup_query = """
+    DELETE FROM hashtags WHERE id IN
+      (SELECT hashtags.id FROM hashtags
+        LEFT OUTER JOIN hashtags_objects
+          ON hashtags_objects.hashtag_id = hashtags.id
+        WHERE hashtags_objects.hashtag_id IS NULL);
+    """
+
+    {:ok, %{num_rows: hashtags_objects_count}} =
+      Repo.query(hashtags_objects_cleanup_query, [], timeout: :infinity)
+
+    {:ok, %{num_rows: hashtags_count}} =
+      Repo.query(hashtags_cleanup_query, [], timeout: :infinity)
+
+    {:ok, hashtags_objects_count, hashtags_count}
+  end
+end