Optimize software/versions queries.

changes/34677-software-versions-endpoint

@@ -0,0 +1 @@
+Improved performance of `/api/latest/fleet/software/versions` API endpoint.

frontend/pages/SoftwarePage/SoftwareTitles/SoftwareTitles.tsx

@@ -134,6 +134,15 @@ const SoftwareTitles = ({
     }
   );
 
+  // This query checks if there are any installable software titles (VPP apps or Fleet-managed
+  // installers) available for the team. It only runs when the versions table is empty, to
+  // determine which empty state message to show:
+  // - If installable software exists: "Install software on your hosts to see versions."
+  // - If no installable software: "Expecting to see software? Check back later."
+  // See PR #21118 (issue #21053) for context.
+  //
+  // The enabled condition ensures this query only fires after the versions query has fully loaded
+  // and confirmed it's actually empty, preventing unnecessary API call delay during page transitions.
   const {
     data: titlesAvailableForInstallResponse,
     isFetching: isTitlesAFIFetching,
@@ -164,7 +173,9 @@ const SoftwareTitles = ({
       ...QUERY_OPTIONS,
       enabled:
         location.pathname === PATHS.SOFTWARE_VERSIONS &&
-        versionsData &&
+        !isVersionsLoading &&
+        !isVersionsFetching &&
+        versionsData !== undefined &&
         versionsData.count === 0,
     }
   );

server/datastore/mysql/common_mysql/retry.go

@@ -77,10 +77,10 @@ func WithRetryTxx(ctx context.Context, db *sqlx.DB, fn TxFn, logger log.Logger)
 	return backoff.Retry(operation, bo)
 }
 
-// retryableError determines whether a MySQL error can be retried. By default
+// RetryableError determines whether a MySQL error can be retried. By default
 // errors are considered non-retryable. Only errors that we know have a
 // possibility of succeeding on a retry should return true in this function.
-func retryableError(err error) bool {
+func RetryableError(err error) bool {
 	base := ctxerr.Cause(err)
 	if b, ok := base.(*mysql.MySQLError); ok {
 		switch b.Number {
@@ -95,3 +95,9 @@ func retryableError(err error) bool {
 
 	return false
 }
+
+// retryableError is the internal (non-exported) version that calls RetryableError.
+// Kept for backwards compatibility with existing callers in this package.
+func retryableError(err error) bool {
+	return RetryableError(err)
+}

server/datastore/mysql/migrations/tables/20251117020000_OptimizeSoftwareHostCountsIndex.go

@@ -0,0 +1,40 @@
+package tables
+
+import (
+	"database/sql"
+	"fmt"
+)
+
+func init() {
+	MigrationClient.AddMigration(Up_20251117020000, Down_20251117020000)
+}
+
+func Up_20251117020000(tx *sql.Tx) error {
+	// Drop the old index that doesn't include global_stats
+	_, err := tx.Exec(`
+			DROP INDEX idx_software_host_counts_team_id_hosts_count_software_id
+			ON software_host_counts
+		`)
+	if err != nil {
+		return fmt.Errorf("failed to drop old index: %w", err)
+	}
+
+	// Create new optimized index with global_stats and DESC on hosts_count
+	// This allows MySQL to:
+	// 1. Seek directly to team_id + global_stats combination
+	// 2. Read rows in descending hosts_count order (already sorted)
+	// 3. Stop after finding LIMIT rows
+	_, err = tx.Exec(`
+			CREATE INDEX idx_software_host_counts_team_global_hosts_desc
+			ON software_host_counts (team_id, global_stats, hosts_count DESC, software_id)
+		`)
+	if err != nil {
+		return fmt.Errorf("failed to create new index: %w", err)
+	}
+
+	return nil
+}
+
+func Down_20251117020000(_ *sql.Tx) error {
+	return nil
+}