matcher: cache query results for the same query

There is a possiblity that if the index record is referring to the same
package but different repositories and the Query() function isn't adding
a matcher constraint for the repository, queries to the DB can end up
being identical. This patch makes sure that the same query is only
executed once by caching the results and using them for subsequent
calls.

Signed-off-by: crozzy <joseph.crosland@gmail.com>

datastore/postgres/get.go

@@ -36,6 +36,11 @@ var (
 	)
 )
 
+type recordQuery struct {
+	record *claircore.IndexRecord
+	query  string
+}
+
 // Get implements vulnstore.Vulnerability.
 func (s *MatcherStore) Get(ctx context.Context, records []*claircore.IndexRecord, opts datastore.GetOpts) (map[string][]*claircore.Vulnerability, error) {
 	ctx = zlog.ContextWithValues(ctx, "component", "internal/vulnstore/postgres/Get")
@@ -46,6 +51,8 @@ func (s *MatcherStore) Get(ctx context.Context, records []*claircore.IndexRecord
 	defer tx.Rollback(ctx)
 	// start a batch
 	batch := &pgx.Batch{}
+	resCache := map[string]pgx.Rows{}
+	rqs := []*recordQuery{}
 	for _, record := range records {
 		query, err := buildGetQuery(record, &opts)
 		if err != nil {
@@ -56,8 +63,13 @@ func (s *MatcherStore) Get(ctx context.Context, records []*claircore.IndexRecord
 				Msg("could not build query for record")
 			continue
 		}
+		rqs = append(rqs, &recordQuery{query: query, record: record})
+		if _, ok := resCache[query]; ok {
+			continue
+		}
 		// queue the select query
 		batch.Queue(query)
+		resCache[query] = nil
 	}
 	// send the batch
 
@@ -70,11 +82,18 @@ func (s *MatcherStore) Get(ctx context.Context, records []*claircore.IndexRecord
 	// gather all the returned vulns for each queued select statement
 	results := make(map[string][]*claircore.Vulnerability)
 	vulnSet := make(map[string]map[string]struct{})
-	for _, record := range records {
-		rows, err := res.Query()
-		if err != nil {
-			res.Close()
-			return nil, err
+	for _, rq := range rqs {
+		rows, ok := resCache[rq.query]
+		if !ok {
+			return nil, fmt.Errorf("unexpected vulnerability query: %s", rq.query)
+		}
+		if rows == nil {
+			rows, err = res.Query()
+			if err != nil {
+				res.Close()
+				return nil, err
+			}
+			resCache[rq.query] = rows
 		}
 
 		// unpack all returned rows into claircore.Vulnerability structs
@@ -121,7 +140,7 @@ func (s *MatcherStore) Get(ctx context.Context, records []*claircore.IndexRecord
 				return nil, fmt.Errorf("failed to scan vulnerability: %v", err)
 			}
 
-			rid := record.Package.ID
+			rid := rq.record.Package.ID
 			if _, ok := vulnSet[rid]; !ok {
 				vulnSet[rid] = make(map[string]struct{})
 			}