more iops cheese testing - sort by downloaded_at not host id

pipeline/04_best_icon/select.sql

@@ -21,7 +21,7 @@ SET work_mem = '2GB';
 \timing on
 
 CREATE TEMP TABLE best_icons AS
-SELECT DISTINCT ON (host_id) host_id, icon_hash
+SELECT DISTINCT ON (host_id) host_id, icon_hash, downloaded_at
 FROM icons
 WHERE scan_state = 'completed'
   AND icon_hash IS NOT NULL
@@ -50,7 +50,7 @@ ORDER BY host_id,
 
 \echo 'Step 2: Updating hosts...'
 
-UPDATE hosts h SET best_icon_hash = b.icon_hash
+UPDATE hosts h SET best_icon_hash = b.icon_hash, icon_downloaded_at = b.downloaded_at
 FROM best_icons b WHERE h.id = b.host_id;
 
 \timing off

pipeline/05_bundle_gen/db.go

@@ -2,7 +2,9 @@ package main
 
 import (
 	"context"
+	"time"
 
+	"github.com/jackc/pgx/v5"
 	"github.com/jackc/pgx/v5/pgxpool"
 )
 
@@ -13,19 +15,43 @@ type HostRow struct {
 	HtmlTitle        string
 	IframeAllowed    bool
 	BestIconHash     string
+	IconDownloadedAt *time.Time
 }
 
-// fetchHostsPage gets a page of hosts with titles, ordered by id for disk locality.
+// fetchHostsPage gets a page of hosts with titles, ordered by icon_downloaded_at for disk locality.
-// Icons were downloaded roughly in host-ID order, so reading by ID approximates
+// Icons written to disk at similar times are physically adjacent on the EBS volume —
-// the physical write order on disk — improves EBS readahead cache hits.
+// reading in write order maximizes OS readahead cache hits.
-func fetchHostsPage(ctx context.Context, pool *pgxpool.Pool, lastID int64, limit int) ([]HostRow, error) {
+func fetchHostsPage(ctx context.Context, pool *pgxpool.Pool, lastTime *time.Time, lastID int64, limit int) ([]HostRow, error) {
-	rows, err := pool.Query(ctx, `
+	// Two-phase: first hosts with icons (ordered by download time), then hosts without
-		SELECT id, hostname, protocol, html_title, COALESCE(iframe_allowed, true), COALESCE(best_icon_hash, '')
+	var rows pgx.Rows
+	var err error
+	if lastTime != nil {
+		rows, err = pool.Query(ctx, `
+			SELECT id, hostname, protocol, html_title, COALESCE(iframe_allowed, true), COALESCE(best_icon_hash, ''), icon_downloaded_at
 			FROM hosts
-		WHERE html_title IS NOT NULL AND id > $1
+			WHERE html_title IS NOT NULL AND icon_downloaded_at > $1
+			ORDER BY icon_downloaded_at
+			LIMIT $2
+		`, lastTime, limit)
+	} else if lastID > 0 {
+		// No more timestamped hosts — fetch remaining (no icon) by id
+		rows, err = pool.Query(ctx, `
+			SELECT id, hostname, protocol, html_title, COALESCE(iframe_allowed, true), '', NULL::timestamptz
+			FROM hosts
+			WHERE html_title IS NOT NULL AND icon_downloaded_at IS NULL AND id > $1
 			ORDER BY id
 			LIMIT $2
 		`, lastID, limit)
+	} else {
+		// Start: fetch timestamped hosts first
+		rows, err = pool.Query(ctx, `
+			SELECT id, hostname, protocol, html_title, COALESCE(iframe_allowed, true), COALESCE(best_icon_hash, ''), icon_downloaded_at
+			FROM hosts
+			WHERE html_title IS NOT NULL AND icon_downloaded_at IS NOT NULL
+			ORDER BY icon_downloaded_at
+			LIMIT $1
+		`, limit)
+	}
 	if err != nil {
 		return nil, err
 	}
@@ -34,7 +60,7 @@ func fetchHostsPage(ctx context.Context, pool *pgxpool.Pool, lastID int64, limit
 	var hosts []HostRow
 	for rows.Next() {
 		var h HostRow
-		if err := rows.Scan(&h.ID, &h.Hostname, &h.Protocol, &h.HtmlTitle, &h.IframeAllowed, &h.BestIconHash); err != nil {
+		if err := rows.Scan(&h.ID, &h.Hostname, &h.Protocol, &h.HtmlTitle, &h.IframeAllowed, &h.BestIconHash, &h.IconDownloadedAt); err != nil {
 			return nil, err
 		}
 		hosts = append(hosts, h)

pipeline/05_bundle_gen/main.go

@@ -128,7 +128,9 @@ func main() {
 	// Stage 1: DB fetcher — continuously fetches pages into hostCh
 	go func() {
 		defer close(hostCh)
+		var lastTime *time.Time
 		var lastID int64
+		iconPhase := true // first: hosts with icons (by download time), then: hosts without
 		pageSize := 50000
 		fetched := 0
 		for {
@@ -143,14 +145,26 @@ func main() {
 				}
 			}
 			fetchStart := time.Now()
-			hosts, err := fetchHostsPage(ctx, pool, lastID, limit)
+			hosts, err := fetchHostsPage(ctx, pool, lastTime, lastID, limit)
 			if err != nil {
 				log.Fatalf("Failed to fetch hosts: %v", err)
 			}
 			if len(hosts) == 0 {
+				if iconPhase {
+					// Switch to no-icon hosts
+					iconPhase = false
+					lastTime = nil
+					lastID = 0
+					continue
+				}
 				break
 			}
-			lastID = hosts[len(hosts)-1].ID
+			last := hosts[len(hosts)-1]
+			if last.IconDownloadedAt != nil {
+				lastTime = last.IconDownloadedAt
+			} else {
+				lastID = last.ID
+			}
 			fmt.Printf("[fetcher] %d hosts in %dms (hostCh: %d/%d)\n",
 				len(hosts), time.Since(fetchStart).Milliseconds(), len(hostCh), cap(hostCh))
 			for _, h := range hosts {