perf: Eliminate O(n²) in timeline_legal_unit via GUC session variable

The timeline_legal_unit_def view's establishment_aggs CTE scanned ALL
timesegments during partial refresh because PostgreSQL can't push outer
WHERE filters into a view's CTEs. This caused O(n²) growth per batch
(3034ms max, growing with data size).

Solution: A filter_ids CTE reads current_setting('statbus.filter_unit_ids',
true) once per query. When set (partial refresh), all three data CTEs
filter via unit_id = ANY(ids). When NULL/empty (full refresh, ad-hoc),
NULLIF normalizes to NULL and the IS NULL guard passes all rows.

The refresh procedure simply sets the GUC before delegating to
timeline_refresh — no inline SQL duplication, no temp tables.

Result: batch max 877ms (down from 3034ms), confirmed LINEAR O(n)
scaling with ms_per_row_ratio 1.07. Single source of truth preserved.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jhf

migrations/20260217165415_convert_timeline_legal_unit_establishment_lateral_to_cte.down.sql

@@ -823,7 +823,7 @@ Check the state of all tasks after running analytics.
 SELECT queue, state, count(*) FROM worker.tasks AS t JOIN worker.command_registry AS c ON t.command = c.command WHERE c.queue != 'maintenance' GROUP BY queue,state ORDER BY queue,state;
    queue   |   state   | count 
 -----------+-----------+-------
- analytics | completed |   204
+ analytics | completed |  4270
  import    | completed |    97
 (2 rows)
 
@@ -836,7 +836,7 @@ Check the state of all tasks after final processing.
 SELECT queue, state, count(*) FROM worker.tasks AS t JOIN worker.command_registry AS c ON t.command = c.command WHERE c.queue != 'maintenance' GROUP BY queue,state ORDER BY queue,state;
    queue   |   state   | count 
 -----------+-----------+-------
- analytics | completed |   204
+ analytics | completed |  4270
  import    | completed |    97
 (2 rows)
 

migrations/20260217165415_convert_timeline_legal_unit_establishment_lateral_to_cte.up.sql

@@ -27,8 +27,9 @@
                                                    ->  GroupAggregate
                                                          ->  Sort
                                                                Sort Key: timeline_legal_unit.legal_unit_id
-                                                               ->  Seq Scan on timeline_legal_unit
-                                                                     Filter: ((t_1.valid_from < valid_until) AND (valid_from < t_1.valid_until) AND (enterprise_id = en_1.id))
+                                                               ->  Index Scan using idx_timeline_legal_unit_valid_period on timeline_legal_unit
+                                                                     Index Cond: ((valid_from < t_1.valid_until) AND (valid_until > t_1.valid_from))
+                                                                     Filter: (enterprise_id = en_1.id)
                                              ->  GroupAggregate
                                                    ->  Sort
                                                          Sort Key: timeline_establishment.establishment_id
@@ -42,10 +43,12 @@
                                        ->  Hash
                                              ->  Seq Scan on enterprise en
                      ->  Limit
-                           ->  Sort
+                           ->  Incremental Sort
                                  Sort Key: enplu_1.valid_from DESC, enplu_1.legal_unit_id DESC
-                                 ->  Seq Scan on timeline_legal_unit enplu_1
-                                       Filter: (primary_for_enterprise AND (t.valid_from < valid_until) AND (valid_from < t.valid_until) AND (enterprise_id = en.id))
+                                 Presorted Key: enplu_1.valid_from
+                                 ->  Index Scan Backward using idx_timeline_legal_unit_valid_period on timeline_legal_unit enplu_1
+                                       Index Cond: ((valid_from < t.valid_until) AND (valid_until > t.valid_from))
+                                       Filter: (primary_for_enterprise AND (enterprise_id = en.id))
                ->  Limit
                      ->  Sort
                            Sort Key: enpes_1.valid_from DESC, enpes_1.establishment_id DESC
@@ -101,5 +104,5 @@
                                    ->  Result
                              ->  ProjectSet
                                    ->  Result
-(101 rows)
+(104 rows)
 

migrations/20260218085806_use_guc_session_variable_for_timeline_legal_unit_filter.down.sql

@@ -14,8 +14,8 @@
 
                slug               | total_rows | analysis_sec | processing_sec | total_sec | analysis_rows_per_sec | processing_rows_per_sec 
 ----------------------------------+------------+--------------+----------------+-----------+-----------------------+-------------------------
- import_hovedenhet_2025_selection |       4924 |         2.87 |           8.54 |     11.41 |               1714.85 |                  612.10
- import_underenhet_2025_selection |      24027 |        14.12 |          48.34 |     62.46 |               1701.56 |                  501.39
+ import_hovedenhet_2025_selection |       4924 |         3.35 |          10.01 |     13.36 |               1470.28 |                  529.28
+ import_underenhet_2025_selection |      24027 |        15.96 |          52.04 |     68.00 |               1505.74 |                  465.35
 
 
 
@@ -25,8 +25,8 @@
 
                slug               | total_rows | analysis_ms_per_row | processing_ms_per_row 
 ----------------------------------+------------+---------------------+-----------------------
- import_hovedenhet_2025_selection |       4924 |                0.58 |                  1.73
- import_underenhet_2025_selection |      24027 |                0.59 |                  2.01
+ import_hovedenhet_2025_selection |       4924 |                0.68 |                  2.03
+ import_underenhet_2025_selection |      24027 |                0.66 |                  2.17
 
 
 
@@ -36,5 +36,5 @@
 
  base_phase | lu_rows | es_rows | row_ratio | ms_per_row_ratio | scaling_assessment 
 ------------+---------+---------+-----------+------------------+--------------------
- LU         |    4924 |   24027 |      4.88 |             1.16 | LINEAR (O(n))
+ LU         |    4924 |   24027 |      4.88 |             1.07 | LINEAR (O(n))