Merge pull request IQSS#10096 from GlobalDataverseCommunityConsortium…

…/IQSS/10095-download_estimate-bug

IQSS/10095-download estimate bug fix

src/main/resources/db/migration/V6.0.0.3__10095-guestbook-at-request2.sql

@@ -0,0 +1,34 @@
+-- This creates a function that ESTIMATES the size of the
+-- GuestbookResponse table (for the metrics display), instead
+-- of relying on straight "SELECT COUNT(*) ..."
+-- It uses statistics to estimate the number of guestbook entries
+-- and the fraction of them related to downloads,
+-- i.e. those that weren't created for 'AccessRequest' events.
+-- Significant potential savings for an active installation.
+-- See https://github.com/IQSS/dataverse/issues/8840 and 
+-- https://github.com/IQSS/dataverse/pull/8972 for more details
+
+CREATE OR REPLACE FUNCTION estimateGuestBookResponseTableSize()
+RETURNS bigint AS $$
+DECLARE
+  estimatedsize bigint;
+BEGIN
+  SELECT CASE WHEN relpages<10 THEN 0
+              ELSE ((reltuples / relpages)
+               * (pg_relation_size('public.guestbookresponse') / current_setting('block_size')::int))::bigint
+               * (SELECT CASE WHEN ((select count(*) from pg_stats where tablename='guestbookresponse') = 0 
+                   OR (select array_position(most_common_vals::text::text[], 'AccessRequest') 
+                       FROM pg_stats WHERE tablename='guestbookresponse' AND attname='eventtype') IS NULL) THEN 1
+                   ELSE 1 - (SELECT (most_common_freqs::text::text[])[array_position(most_common_vals::text::text[], 'AccessRequest')]::float
+                       FROM pg_stats WHERE tablename='guestbookresponse' and attname='eventtype') END)
+         END
+     FROM   pg_class
+     WHERE  oid = 'public.guestbookresponse'::regclass INTO estimatedsize;
+
+     if estimatedsize = 0 then
+     SELECT COUNT(id) FROM guestbookresponse WHERE eventtype!= 'AccessRequest' INTO estimatedsize;
+     END if;   
+
+  RETURN estimatedsize;
+END;
+$$ LANGUAGE plpgsql IMMUTABLE;