perf, fix random recipient table scan

Signed-off-by: RonniSkansing <rskansing@gmail.com>

backend/repository/recipient.go

@@ -2,6 +2,7 @@ package repository
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"slices"
 	"strconv"
@@ -744,19 +745,31 @@ func (r *Recipient) GetRandomByCompanyID(
 ) (*model.Recipient, error) {
 	var dbRecipient database.Recipient
 
-	db := r.DB.Table(database.RECIPIENT_TABLE)
-
-	// apply company filter
-	db = whereCompany(db, database.RECIPIENT_TABLE, companyID)
-
-	// exclude specific recipient if provided
-	if excludeRecipientID != nil {
-		db = db.Where(fmt.Sprintf("%s != ?", TableColumnID(database.RECIPIENT_TABLE)), excludeRecipientID)
+	// build the company (and optional exclude) filter into a fresh query each call
+	filtered := func() *gorm.DB {
+		q := r.DB.Table(database.RECIPIENT_TABLE)
+		q = whereCompany(q, database.RECIPIENT_TABLE, companyID)
+		if excludeRecipientID != nil {
+			q = q.Where(fmt.Sprintf("%s != ?", TableColumnID(database.RECIPIENT_TABLE)), excludeRecipientID)
+		}
+		return q
 	}
 
-	// order randomly and get one
-	res := db.Order("RANDOM()").Limit(1).First(&dbRecipient)
-
+	// pick a random rowid threshold and take the first matching row at or after it.
+	// this rides the rowid index; ORDER BY RANDOM instead sorts the whole table on
+	// every call, which gets slower as the recipients table grows. if the threshold
+	// lands past the last match, wrap to the first matching row.
+	res := filtered().
+		Where(fmt.Sprintf(
+			"%[1]s.rowid >= (abs(random()) %% (SELECT max(rowid) + 1 FROM %[1]s))",
+			database.RECIPIENT_TABLE,
+		)).
+		Order(database.RECIPIENT_TABLE + ".rowid").
+		Limit(1).
+		First(&dbRecipient)
+	if errors.Is(res.Error, gorm.ErrRecordNotFound) {
+		res = filtered().Order(database.RECIPIENT_TABLE + ".rowid").Limit(1).First(&dbRecipient)
+	}
 	if res.Error != nil {
 		return nil, res.Error
 	}

backend/service/templateService.go

@@ -78,8 +78,21 @@ func (t *Template) CreateMail(
 		apiSender,
 	)
 
-	// add random recipient data to template context (excluding current recipient)
-	(*data)["RandomRecipient"] = t.getRandomRecipientData(ctx, companyID, &rid)
+	// add random recipient data only when the email actually uses it (the lookup is
+	// costly), excluding the current recipient
+	if email != nil {
+		subject := ""
+		if v, err := email.MailHeaderSubject.Get(); err == nil {
+			subject = v.String()
+		}
+		content := ""
+		if v, err := email.Content.Get(); err == nil {
+			content = v.String()
+		}
+		if usesRandomRecipient(subject, content) {
+			(*data)["RandomRecipient"] = t.getRandomRecipientData(ctx, companyID, &rid)
+		}
+	}
 
 	// full report endpoint URL for this recipient on the campaign domain, so a report
 	// header can carry a ready-to-call link instead of just the token
@@ -524,12 +537,15 @@ func (t *Template) CreatePhishingPageWithCampaignAndRecipient(
 		nil, // apiSender
 	)
 
-	// add random recipient data to template context (excluding current recipient)
-	var excludeRecipientID *uuid.UUID
-	if rid, err := recipient.ID.Get(); err == nil {
-		excludeRecipientID = &rid
+	// add random recipient data only when the page template uses it (the lookup is
+	// costly), excluding the current recipient
+	if usesRandomRecipient(contentToRender) {
+		var excludeRecipientID *uuid.UUID
+		if rid, err := recipient.ID.Get(); err == nil {
+			excludeRecipientID = &rid
+		}
+		(*data)["RandomRecipient"] = t.getRandomRecipientData(ctx, companyID, excludeRecipientID)
 	}
-	(*data)["RandomRecipient"] = t.getRandomRecipientData(ctx, companyID, excludeRecipientID)
 
 	// direct URLs to each stage of the flow, available when this page is served as part
 	// of a real campaign. before and after stay empty when the flow has no such stage.
@@ -953,6 +969,18 @@ func (t *Template) TemplateFuncsWithDeviceCode(
 	return funcs
 }
 
+// usesRandomRecipient reports whether any of the template texts reference the
+// RandomRecipient variable. The random recipient lookup is costly, so it is only
+// done when a template actually uses it.
+func usesRandomRecipient(texts ...string) bool {
+	for _, s := range texts {
+		if strings.Contains(s, "RandomRecipient") {
+			return true
+		}
+	}
+	return false
+}
+
 // getRandomRecipientData gets a random recipient from a company and returns a map of their data
 func (t *Template) getRandomRecipientData(ctx context.Context, companyID *uuid.UUID, excludeRecipientID *uuid.UUID) map[string]string {
 	data := map[string]string{