Rewritten list query, test and fix [#82]

pkg/kine/drivers/generic/generic.go

@@ -24,14 +24,17 @@ var (
 
 	listSQL = fmt.Sprintf(`
 		SELECT %s
-		FROM kine AS kv
-			LEFT JOIN kine kv2
-				ON kv.name = kv2.name
-				AND kv.id < kv2.id
-		WHERE kv2.name IS NULL
-			AND kv.name >= ? AND kv.name < ?
-			AND (? OR kv.deleted = 0)
-			%%s
+		FROM kine kv
+		JOIN (
+			SELECT MAX(mkv.id) as id
+			FROM kine mkv
+			WHERE
+				mkv.name >= ? AND mkv.name < ?
+				%%s
+			GROUP BY mkv.name) maxkv
+	    	ON maxkv.id = kv.id
+		WHERE
+			  (kv.deleted = 0 OR ?)
 		ORDER BY kv.id ASC
 	`, columns)
 
@@ -200,7 +203,7 @@ func Open(ctx context.Context, driverName, dataSourceName string, paramCharacter
 			WHERE kv.id = ?`, columns), paramCharacter, numbered),
 
 		GetCurrentSQL:        q(fmt.Sprintf(listSQL, ""), paramCharacter, numbered),
-		ListRevisionStartSQL: q(fmt.Sprintf(listSQL, "AND kv.id <= ?"), paramCharacter, numbered),
+		ListRevisionStartSQL: q(fmt.Sprintf(listSQL, "AND mkv.id <= ?"), paramCharacter, numbered),
 		GetRevisionAfterSQL:  q(revisionAfterSQL, paramCharacter, numbered),
 
 		CountSQL: q(fmt.Sprintf(`

test/update_test.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"testing"
+	"time"
 
 	. "github.com/onsi/gomega"
 	clientv3 "go.etcd.io/etcd/client/v3"
@@ -77,6 +78,24 @@ func TestUpdate(t *testing.T) {
 			g.Expect(resp.Kvs[0].ModRevision).To(BeNumerically(">", resp.Kvs[0].CreateRevision))
 		}
 	})
+	t.Run("UpdateSameKeyLinearity", func(t *testing.T) {
+		g := NewWithT(t)
+
+		// Add a large number of entries, two times and
+		// it should take approximately same amout of time
+		numAddEntries := 1000
+
+		startFirst := time.Now()
+		addSameEntries(ctx, g, client, numAddEntries, true)
+		durationFirstBatch := time.Since(startFirst)
+
+		startSecond := time.Now()
+		addSameEntries(ctx, g, client, numAddEntries, false)
+		durationSecondBatch := time.Since(startSecond)
+
+		g.Expect(durationSecondBatch <= durationFirstBatch*2).To(BeTrue())
+
+	})
 
 	// Trying to update an old revision(in compare) should fail
 	t.Run("UpdateOldRevisionFails", func(t *testing.T) {
@@ -125,6 +144,37 @@ func TestUpdate(t *testing.T) {
 
 }
 
+func addSameEntries(ctx context.Context, g Gomega, client *clientv3.Client, numEntries int, create_first bool) {
+	for i := 0; i < numEntries; i++ {
+		key := "testkey-same"
+		value := fmt.Sprintf("value-%d", i)
+
+		if i != 0 || !create_first {
+			updateEntry(ctx, g, client, key, value)
+		} else {
+			addEntry(ctx, g, client, key, value)
+		}
+	}
+}
+
+func updateEntry(ctx context.Context, g Gomega, client *clientv3.Client, key string, value string) {
+
+	resp, err := client.Get(ctx, key, clientv3.WithRange(""))
+
+	g.Expect(err).To(BeNil())
+	g.Expect(resp.Kvs).To(HaveLen(1))
+
+	resp2, err2 := client.Txn(ctx).
+		If(clientv3.Compare(clientv3.ModRevision(key), "=", resp.Kvs[0].ModRevision)).
+		Then(clientv3.OpPut(key, value)).
+		Else(clientv3.OpGet(key, clientv3.WithRange(""))).
+		Commit()
+
+	g.Expect(err2).To(BeNil())
+	g.Expect(resp2.Succeeded).To(BeTrue())
+
+}
+
 // BenchmarkUpdate is a benchmark for the Update operation.
 func BenchmarkUpdate(b *testing.B) {
 	ctx := context.Background()