Support upserts in database

This is required as codespaces' state will change over time

metrics/timescaledb/db.py

@@ -12,22 +12,42 @@
 log = structlog.get_logger()
 
 
+MAX_PARAMS = 65535  # limit for postgresql
+
+
 def reset_table(table, batch_size=None):
     _drop_table(table, batch_size)
     _ensure_table(table)
     log.info("Reset table", table=table.name)
 
 
 def write(table, rows):
-    max_params = 65535  # limit for postgresql
-    batch_size = max_params // len(table.columns)
+    batch_size = _batch_size(table)
 
     with _get_engine().begin() as connection:
         for values in batched(rows, batch_size):
             connection.execute(insert(table).values(values))
             log.info("Inserted %s rows", len(values), table=table.name)
 
 
+def upsert(table, rows):
+    _ensure_table(table)
+    batch_size = _batch_size(table)
+    non_pk_columns = set(table.columns) - set(table.primary_key.columns)
+
+    with _get_engine().begin() as connection:
+        for values in batched(rows, batch_size):
+            insert_stmt = insert(table).values(values)
+
+            set_ = {c: insert_stmt.excluded[c.name] for c in non_pk_columns}
+
+            insert_stmt = insert_stmt.on_conflict_do_update(
+                constraint=table.primary_key, set_=set_
+            )
+            connection.execute(insert_stmt)
+            log.info("Inserted %s rows", len(values), table=table.name)
+
+
 def _drop_table(table, batch_size):
     with _get_engine().begin() as connection:
         log.debug("Removing table: %s", table.name)
@@ -114,6 +134,10 @@ def _ensure_table(table):
             )
 
 
+def _batch_size(table):
+    return MAX_PARAMS // len(table.columns)
+
+
 @functools.cache
 def _get_engine():
     return create_engine(_get_url())

tests/metrics/timescaledb/test_db.py

@@ -164,3 +164,33 @@ def test_write(engine, table):
     # check rows are in table
     rows = get_rows(engine, table)
     assert len(rows) == 3
+
+
+def test_upsert(engine, table):
+    # add a non-PK column to the table
+    table.append_column(Column("value2", Text))
+
+    # set up a table to upsert into
+    db._ensure_table(table)
+
+    # insert intital rows
+    rows = [{"value": i, "value2": i} for i in range(1, 4)]
+
+    db.upsert(table, rows)
+
+    # second batch of rows, some with differing value2s, some new
+    rows = [{"value": i, "value2": 2 * i} for i in range(3, 6)]
+
+    db.upsert(table, rows)
+
+    # check rows are in table
+    rows = get_rows(engine, table)
+    assert len(rows) == 5
+
+    # check upsert leaves unmatched rows intact
+    original_rows = [int(r[0]) / int(r[1]) for r in rows if int(r[0]) < 3]
+    assert set(original_rows) == {1}
+
+    # check upsert modifies matched rows
+    modified_rows = [int(r[0]) / int(r[1]) for r in rows if int(r[0]) >= 3]
+    assert set(modified_rows) == {0.5}