[IMP] snippets: move all work from parent to mp workers

In `convert_html_columns()`, we select 100MiB worth of DB tuples and pass them
to a ProcessPoolExecutor together with a converter callable. So far, the
converter returns all tuples, changed or unchanged together with the
information if it has changed something. All this is returned through IPC to
the parent process. In the parent process, the caller only acts on the changed
tuples, though, the rest is ignored. In any scenario I've seen, only a small
proportion of the input tuples is actually changed, meaning that a large
proportion is returned through IPC unnecessarily.

What makes it worse is that processing of the converted results in the parent
process is often slower than the conversion, leading to two effects:
1) The results of all workers sit in the parent process's memory, possibly
   leading to MemoryError (upg-2021031)
2) The parallel processing is being serialized on the feedback, defeating a
   large part of the intended performance gains

To improve this, this commit
- moves all work into the workers, meaning not just the conversion filter, but
  also the DB query as well as the DB updates.
  - by doing so reduces the amount of data passed by IPC to just the query
    texts
  - by doing so distributes the data held in memory to all worker processes
- reduces the chunk size by one order of magnitude, which means
  - a lot less memory used at a time
  - a lot better distribution of "to-be-changed" rows when these rows are
    clustered in the table

All in all, in my test case, this
- reduces maximum process size in memory to 300MiB for all processes compared
  to formerly >2GiB (and MemoryError) in the parent process
- reduces runtime from 17 minutes to less than 2 minutes

Author: cawo-odoo

src/base/tests/test_util.py

@@ -15,7 +15,7 @@
 except ImportError:
     import mock
 
-from odoo import modules
+from odoo import SUPERUSER_ID, api, modules
 from odoo.tools import mute_logger
 
 from odoo.addons.base.maintenance.migrations import util
@@ -1965,24 +1965,27 @@ def testsnip(self):
                 </script>
             </html>
         """
-        view_id = self.env["ir.ui.view"].create(
-            {
-                "name": "not_for_anything",
-                "type": "qweb",
-                "mode": "primary",
-                "key": "test.htmlconvert",
-                "arch_db": view_arch,
-            }
-        )
-        cr = self.env.cr
-        snippets.convert_html_content(
-            cr,
-            snippets.html_converter(
-                not_doing_anything_converter, selector="//*[hasclass('fake_class_not_doing_anything')]"
-            ),
-        )
-        util.invalidate(view_id)
-        res = self.env["ir.ui.view"].search_read([("id", "=", view_id.id)], ["arch_db"])
+        vals = {
+            "name": "not_for_anything",
+            "type": "qweb",
+            "mode": "primary",
+            "key": "test.htmlconvert",
+            "arch_db": view_arch,
+        }
+        # util.convert_html_columns() commits the cursor, use a new transaction to not mess up the test_cr
+        with self.registry.cursor() as cr:
+            env = api.Environment(cr, SUPERUSER_ID, {})
+            view_id = env["ir.ui.view"].create(vals)
+            snippets.convert_html_content(
+                cr,
+                snippets.html_converter(
+                    not_doing_anything_converter, selector="//*[hasclass('fake_class_not_doing_anything')]"
+                ),
+            )
+            util.invalidate(view_id)
+            res = env["ir.ui.view"].search_read([("id", "=", view_id.id)], ["arch_db"])
+            # clean up committed data
+            view_id.unlink()
         self.assertEqual(len(res), 1)
         oneline = lambda s: re.sub(r"\s+", " ", s.strip())
         self.assertEqual(oneline(res[0]["arch_db"]), oneline(view_arch))

src/util/snippets.py

@@ -1,4 +1,6 @@
 # -*- coding: utf-8 -*-
+import concurrent
+import contextlib
 import inspect
 import logging
 import re
@@ -11,6 +13,9 @@
 from psycopg2.extensions import quote_ident
 from psycopg2.extras import Json
 
+with contextlib.suppress(ImportError):
+    from odoo.sql_db import db_connect
+
 from .const import NEARLYWARN
 from .exceptions import MigrationError
 from .helpers import table_of_model
@@ -243,11 +248,24 @@ def _dumps(self, node):
 
 
 class Convertor:
-    def __init__(self, converters, callback):
+    def __init__(self, converters, callback, dbname=None, update_query=None):
         self.converters = converters
         self.callback = callback
-
-    def __call__(self, row):
+        self.dbname = dbname
+        self.update_query = update_query
+
+    def __call__(self, row_or_query):
+        # backwards compatibility: caller passes rows and expects us to return them converted
+        if not self.dbname:
+            return self._convert_row(row_or_query)
+        # improved interface: caller passes a query for us to fetch input rows, convert and update them
+        with db_connect(self.dbname).cursor() as cr:
+            cr.execute(row_or_query)
+            for changes in filter(None, map(self._convert_row, cr.fetchall())):
+                cr.execute(self.update_query, changes)
+        return None
+
+    def _convert_row(self, row):
         converters = self.converters
         columns = self.converters.keys()
         converter_callback = self.callback
@@ -267,7 +285,7 @@ def __call__(self, row):
             changes[column] = new_content
             if has_changed:
                 changes["id"] = res_id
-        return changes
+        return changes if "id" in changes else None
 
 
 def convert_html_columns(cr, table, columns, converter_callback, where_column="IS NOT NULL", extra_where="true"):
@@ -305,17 +323,25 @@ def convert_html_columns(cr, table, columns, converter_callback, where_column="I
     update_sql = ", ".join(f'"{column}" = %({column})s' for column in columns)
     update_query = f"UPDATE {table} SET {update_sql} WHERE id = %(id)s"
 
+    cr.commit()
     with ProcessPoolExecutor(max_workers=get_max_workers()) as executor:
-        convert = Convertor(converters, converter_callback)
-        for query in log_progress(split_queries, logger=_logger, qualifier=f"{table} updates"):
-            cr.execute(query)
-            for data in executor.map(convert, cr.fetchall(), chunksize=1000):
-                if "id" in data:
-                    cr.execute(update_query, data)
+        convert = Convertor(converters, converter_callback, cr.dbname, update_query)
+        futures = [executor.submit(convert, query) for query in split_queries]
+        for future in log_progress(
+            concurrent.futures.as_completed(futures),
+            logger=_logger,
+            qualifier=f"{table} updates",
+            size=len(split_queries),
+            estimate=False,
+            log_hundred_percent=True,
+        ):
+            # just for raising any worker exception
+            future.result()
+    cr.commit()
 
 
 def determine_chunk_limit_ids(cr, table, column_arr, where):
-    bytes_per_chunk = 100 * 1024 * 1024
+    bytes_per_chunk = 10 * 1024 * 1024
     columns = ", ".join(quote_ident(column, cr._cnx) for column in column_arr if column != "id")
     cr.execute(
         f"""