improve performance of multi-class searches

Backport of trunk commit 18233.

For as yet unknown reasons, Postgres sometimes uses
nested loops instead of hash joins when joining subqueries
in a multi-class bib search.  This can result in searches
such as "author:rowling title:harry potter" never completing.

Removing the interior limit clause can both speed up the query
and make search results more accurate when combining queries
of two or more common words.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
git-svn-id: svn://svn.open-ils.org/ILS/branches/rel_1_6_0@19265 dcc99617-32d9-48b4-a31d-7c20da2025e4

diff --git a/Open-ILS/src/sql/Pg/300.schema.staged_search.sql b/Open-ILS/src/sql/Pg/300.schema.staged_search.sql
index 30ef658..aaa73b7 100644 (file)
--- a/Open-ILS/src/sql/Pg/300.schema.staged_search.sql
+++ b/Open-ILS/src/sql/Pg/300.schema.staged_search.sql
@@ -232,7 +232,7 @@ BEGIN
 
         from_clause := from_clause ||
             ' JOIN ( SELECT * FROM ' || query_table || ' WHERE ' || inner_where_clause ||
-                    CASE WHEN core_rel_limit > 0 THEN ' LIMIT ' || core_rel_limit::TEXT ELSE '' END || ' ) AS ' || query_part.table_alias ||
+                    ' ) AS ' || query_part.table_alias ||
                 ' ON ( m.source = ' || query_part.table_alias || '.source )' ||
             ' JOIN config.metabib_field AS ' || query_part.table_alias || '_weight' ||
                 ' ON ( ' || query_part.table_alias || '.field = ' || query_part.table_alias || '_weight.id  AND  ' || query_part.table_alias || '_weight.search_field)';
@@ -349,7 +349,8 @@ BEGIN
     END IF;
 
     core_rel_query := select_clause || from_clause || where_clause ||
-                        ' GROUP BY 1 ORDER BY 4' || CASE WHEN sort_desc THEN ' DESC' ELSE ' ASC' END || ';';
+                        ' GROUP BY 1 ORDER BY 4' || CASE WHEN sort_desc THEN ' DESC' ELSE ' ASC' END ||
+                        CASE WHEN core_rel_limit > 0 THEN ' LIMIT ' || core_rel_limit::TEXT ELSE '' END || ';';
     --RAISE NOTICE 'Base Query:  %', core_rel_query;
 
     IF param_search_ou > 0 THEN