Add alembic migration path

alembic/versions/eff1387cfd0b_add_deletedconversation_table.py

@@ -0,0 +1,33 @@
+"""add deletedconversation table
+
+Revision ID: eff1387cfd0b
+Revises: bd57477f19a2
+Create Date: 2022-02-24 13:11:22.227528
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = 'eff1387cfd0b'
+down_revision = 'bd57477f19a2'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    # Add deletedconversation table to manage locally-deleted records
+    # and ensure they do not get re-downloaded to the database during
+    # a network race condition.
+    # UUID was chosen as PK to avoid storing data such as source_id that
+    # could divulge information about the source account creation timeline.
+    # Note that records in this table are purged every 15 seconds.
+    op.create_table('deletedconversation',
+    sa.Column('uuid', sa.String(length=36), nullable=False),
+    sa.PrimaryKeyConstraint('uuid', name=op.f('pk_deletedconversation'))
+    )
+
+
+def downgrade():
+    op.drop_table('deletedconversation')