From: Bill Erickson <berickxx@gmail.com>
Date: Thu, 15 Mar 2018 15:16:25 +0000 (-0400)
Subject: JBAS-1997 Prevent sequential scans in hold queue pos func
X-Git-Url: https://old-git.evergreen-ils.org/?a=commitdiff_plain;h=213ed9b3c964e9d1d5e8bef0b0ad87356c9e962c;p=working%2FEvergreen.git

JBAS-1997 Prevent sequential scans in hold queue pos func

Brute-force the PG planner to make it use index scans instead of
sequential scans in the hold queue position stored proc.  This resolves
a problem where the planner starts using seq scans over time as the
stats morph in the presence of lots of active, large-queue holds.

Avoidin the seq scan shows consistently better performance.

Signed-off-by: Bill Erickson <berickxx@gmail.com>
---

diff --git a/KCLS/sql/schema/deploy/hold-queue-pos-func.sql b/KCLS/sql/schema/deploy/hold-queue-pos-func.sql
index d63e29b35a..fec832877e 100644
--- a/KCLS/sql/schema/deploy/hold-queue-pos-func.sql
+++ b/KCLS/sql/schema/deploy/hold-queue-pos-func.sql
@@ -18,6 +18,7 @@ DECLARE
     related_id INTEGER;
     queue_pos INTEGER DEFAULT 1;
 BEGIN
+    SET enable_seqscan = false;
     FOR related_id IN SELECT id FROM (
         SELECT ahr.id, ahr.cut_in_line, ahr.request_time
         FROM action.hold_request ahr
@@ -29,10 +30,12 @@ BEGIN
         ORDER BY COALESCE (ahr.cut_in_line, FALSE) DESC, ahr.request_time
     ) related_holds LOOP
         IF related_id = hold_id THEN
+            RESET enable_seqscan;
             RETURN queue_pos;
         END IF;
         queue_pos = queue_pos + 1;
     END LOOP;
+    RESET enable_seqscan;
     RETURN -1; -- No such hold
 END;
 $FUNK$ LANGUAGE PLPGSQL;