05/06 Fix some notable and quality issues

migrations/versions/phase15_audit_log_indexes.py

@@ -0,0 +1,62 @@
+"""phase15 — add indexes on audit_logs action and entity_type
+
+The audit log filter UI allows filtering by action and entity_type.
+Without indexes, every filter invocation performs a full table scan.
+As the log grows toward the 180/365-day purge threshold this degrades
+noticeably.  This migration adds individual indexes on both columns.
+
+A composite index on (action, entity_type, created_at) would be ideal
+for the combined-filter case, but individual indexes are added here to
+keep the migration additive and safe for re-run.  created_at already
+has an index from the model definition.
+
+Existence checks use information_schema so the migration is safe to
+re-run on any MySQL version (compatible back to 5.7).
+
+Revision ID: phase15_audit_log_indexes
+Revises: phase14_facility_created_at
+"""
+
+revision      = 'phase15_audit_log_indexes'
+down_revision = 'phase14_facility_created_at'
+branch_labels = None
+depends_on    = None
+
+from alembic import op
+from sqlalchemy import text
+
+
+def _index_exists(conn, table: str, index_name: str) -> bool:
+    """Return True if the named index already exists on the given table."""
+    result = conn.execute(text(
+        "SELECT COUNT(*) FROM information_schema.statistics "
+        "WHERE table_schema = DATABASE() "
+        "  AND table_name   = :table "
+        "  AND index_name   = :index"
+    ), {'table': table, 'index': index_name})
+    return result.scalar() > 0
+
+
+# (table, index_name, column)
+INDEXES = [
+    ('audit_logs', 'ix_audit_logs_action',      'action'),
+    ('audit_logs', 'ix_audit_logs_entity_type', 'entity_type'),
+]
+
+
+def upgrade():
+    conn = op.get_bind()
+    for table, index_name, column in INDEXES:
+        if not _index_exists(conn, table, index_name):
+            op.execute(text(
+                f'CREATE INDEX {index_name} ON {table} ({column})'
+            ))
+
+
+def downgrade():
+    conn = op.get_bind()
+    for table, index_name, _column in INDEXES:
+        if _index_exists(conn, table, index_name):
+            op.execute(text(
+                f'DROP INDEX {index_name} ON {table}'
+            ))