Enhance documentation, update comments

doc/CDB_Overviews.md

@@ -7,6 +7,8 @@ The *reduction* consists in a fewer number of records
 and/or simplified record geometries.
 
 Overviews are created through the `CDB_CreateOverviews`.
+The statement timeout may need to be adjusted before using this function,
+as overview creation for large tables is a time-consuming operation.
 
 The `CDB_Overviews` function can be used determine what overview tables
 exist for a given dataset table and which zoom levels correspond tt
@@ -31,12 +33,14 @@ SELECT CDB_CreateOverviews('table_name');
 CDB_CreateOverviews(table_name, ref_z_strategy, reduction_strategy)
 
 * **table_name** regclass, table for which overviews will be generated
-* **ref_z_strategy** regproc, function that provides the Z-scale strategy.
+* **ref_z_strategy** regproc, optional function that provides
+  the Z-scale strategy.
   It returns the base Z level for the dataset.
   It should have these arguments:
   - **table_name** regclass, table to compute the reference Z scale for
-* **reduction_strategy** regproc, function that provides the reduction strategy
-  to generate an overview table from a table for a smaller scale (higher Z number).
+* **reduction_strategy** regproc, optional function that provides
+  the reduction strategy to generate an overview table from a table
+  for a smaller scale (higher Z number).
   It returns the name of the generated table.
   It should have these arguments:
   - **base_table_name** regclass, base table to be reduced.

scripts-available/CDB_Overviews.sql

@@ -257,9 +257,8 @@ AS $$
 
     PERFORM _CDB_Add_Indexes(overview_table);
 
-    -- TODO: we'll need to store metadata somewhere to define
-    -- which overlay levels are available. Here we should add this metadata
-    -- (or replace existing metadata)
+    -- TODO: If metadata about existing overviews is to be stored
+    -- it should be done here (CDB_Overviews would consume such metadata)
   END
 $$ LANGUAGE PLPGSQL;
 
@@ -417,7 +416,6 @@ AS $$
     SELECT string_agg(s.column, ',') FROM (
       SELECT * FROM cols
     ) AS s INTO columns;
-    RAISE NOTICE 'COLUMNS: %s', columns;
 
 
     EXECUTE Format('DROP TABLE IF EXISTS %s CASCADE;', overview_rel);
@@ -474,8 +472,6 @@ DECLARE
   overview_tables REGCLASS[];
   overviews_step integer := 1;
 BEGIN
-  -- TODO: adjust statement_timeout here based on input table size?
-
   -- Determine the referece zoom level
   EXECUTE 'SELECT ' || quote_ident(refscale_strategy::text) || Format('(''%s'');', reloid) INTO ref_z;