two phase best icon selection with a temporary table

pipeline/04_best_icon/select.sql

@@ -10,41 +10,52 @@
 --   4. Tiebreaker: smaller file size
 --   SVGs excluded (not supported in bundle generation). Icons ≤2x2 excluded (tracking pixels).
 --
+-- Two-step: SELECT into temp table (index-only scan, no heap), then single bulk UPDATE.
+-- Requires idx_icons_best covering index on (host_id) INCLUDE (s3_key, content_type, width, height, file_size).
+--
 -- Usage: psql $DATABASE_URL -f pipeline/04_best_icon/select.sql
 
-UPDATE hosts h SET best_icon_s3_key = sub.s3_key
-FROM (
-  SELECT DISTINCT ON (i.host_id) i.host_id, i.s3_key
-  FROM icons i
-  WHERE i.scan_state = 'completed'
-    AND i.s3_key IS NOT NULL
-    AND i.content_type != 'image/svg+xml'
-    AND (i.width IS NULL OR i.width > 2)
-    AND (i.height IS NULL OR i.height > 2)
-  ORDER BY i.host_id,
-    -- Tier: ≥32 preferred over <32. NULL dimensions go last.
+SET work_mem = '2GB';
+
+\echo 'Step 1: Finding best icon per host...'
+\timing on
+
+CREATE TEMP TABLE best_icons AS
+SELECT DISTINCT ON (host_id) host_id, s3_key
+FROM icons
+WHERE scan_state = 'completed'
+  AND s3_key IS NOT NULL
+  AND content_type != 'image/svg+xml'
+  AND (width IS NULL OR width > 2)
+  AND (height IS NULL OR height > 2)
+ORDER BY host_id,
   CASE
-      WHEN LEAST(COALESCE(i.width, 0), COALESCE(i.height, 0)) >= 32 THEN 0
-      WHEN COALESCE(i.width, 0) > 0 THEN 1
+    WHEN LEAST(COALESCE(width, 0), COALESCE(height, 0)) >= 32 THEN 0
+    WHEN COALESCE(width, 0) > 0 THEN 1
     ELSE 2
   END,
-    -- Within ≥32: smallest first (closest to 32). Within <32: largest first.
   CASE
-      WHEN LEAST(COALESCE(i.width, 0), COALESCE(i.height, 0)) >= 32
-        THEN GREATEST(COALESCE(i.width, 0), COALESCE(i.height, 0))
-      ELSE -GREATEST(COALESCE(i.width, 0), COALESCE(i.height, 0))
+    WHEN LEAST(COALESCE(width, 0), COALESCE(height, 0)) >= 32
+      THEN GREATEST(COALESCE(width, 0), COALESCE(height, 0))
+    ELSE -GREATEST(COALESCE(width, 0), COALESCE(height, 0))
   END,
-    -- Format preference
   CASE
-      WHEN i.content_type = 'image/png' THEN 0
-      WHEN i.content_type IN ('image/x-icon', 'image/vnd.microsoft.icon') THEN 1
-      WHEN i.content_type IN ('image/gif', 'image/jpeg', 'image/bmp') THEN 2
-      WHEN i.content_type = 'image/webp' THEN 3
+    WHEN content_type = 'image/png' THEN 0
+    WHEN content_type IN ('image/x-icon', 'image/vnd.microsoft.icon') THEN 1
+    WHEN content_type IN ('image/gif', 'image/jpeg', 'image/bmp') THEN 2
+    WHEN content_type = 'image/webp' THEN 3
     ELSE 4
   END,
-    i.file_size ASC
-) sub
-WHERE h.id = sub.host_id;
+  file_size ASC;
+
+\echo 'Step 2: Updating hosts...'
+
+UPDATE hosts h SET best_icon_s3_key = b.s3_key
+FROM best_icons b WHERE h.id = b.host_id;
+
+\timing off
+
+DROP TABLE best_icons;
 
 -- Stats (human-readable)
 \echo '--- Best Icon Selection Stats ---'