chore: add example how to delete keys without a ttl

example/del-keys-without-ttl/README.md

@@ -0,0 +1,11 @@
+# Delete keys without a ttl
+
+This example demonstrates how to use `SCAN` and pipelines to efficiently delete keys without a TTL.
+
+To run this example:
+
+```shell
+go run .
+```
+
+See [documentation](https://redis.uptrace.dev/guide/get-all-keys.html) for more details.

example/del-keys-without-ttl/go.mod

@@ -0,0 +1,7 @@
+module github.com/go-redis/redis/example/del-keys-without-ttl
+
+go 1.14
+
+replace github.com/go-redis/redis/v8 => ../..
+
+require github.com/go-redis/redis/v8 v8.0.0-00010101000000-000000000000

example/del-keys-without-ttl/go.sum

@@ -0,0 +1,101 @@
+github.com/cespare/xxhash/v2 v2.1.2 h1:YRXhKfTDauu4ajMg1TPgFO5jnlC2HCbmLXMcTG5cbYE=
+github.com/cespare/xxhash/v2 v2.1.2/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
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example/del-keys-without-ttl/main.go

@@ -0,0 +1,142 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"sync"
+
+	"github.com/go-redis/redis/v8"
+)
+
+func main() {
+	ctx := context.Background()
+
+	rdb := redis.NewClient(&redis.Options{
+		Addr: ":6379",
+	})
+
+	ch := make(chan string, 100)
+	var wg sync.WaitGroup
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		deleted, err := process(ctx, rdb, ch)
+		if err != nil {
+			panic(err)
+		}
+		fmt.Println("deleted", deleted, "keys")
+	}()
+
+	iter := rdb.Scan(ctx, 0, "", 0).Iterator()
+	for iter.Next(ctx) {
+		ch <- iter.Val()
+	}
+	if err := iter.Err(); err != nil {
+		panic(err)
+	}
+
+	close(ch)
+	wg.Wait()
+}
+
+func process(ctx context.Context, rdb *redis.Client, in <-chan string) (int, error) {
+	var wg sync.WaitGroup
+
+	out := make(chan string, 100)
+	defer func() {
+		close(out)
+		wg.Wait()
+	}()
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		if err := del(ctx, rdb, out); err != nil {
+			panic(err)
+		}
+	}()
+
+	var deleted int
+
+	keys := make([]string, 0, 100)
+	for key := range in {
+		keys = append(keys, key)
+		if len(keys) < 100 {
+			continue
+		}
+
+		var err error
+		keys, err = checkTTL(ctx, rdb, keys)
+		if err != nil {
+			return 0, err
+		}
+
+		for _, key := range keys {
+			out <- key
+		}
+		deleted += len(keys)
+
+		keys = keys[:0]
+	}
+
+	if len(keys) > 0 {
+		keys, err := checkTTL(ctx, rdb, keys)
+		if err != nil {
+			return 0, err
+		}
+
+		for _, key := range keys {
+			out <- key
+		}
+		deleted += len(keys)
+	}
+
+	return deleted, nil
+}
+
+func checkTTL(ctx context.Context, rdb *redis.Client, keys []string) ([]string, error) {
+	cmds, err := rdb.Pipelined(ctx, func(pipe redis.Pipeliner) error {
+		for _, key := range keys {
+			pipe.TTL(ctx, key)
+		}
+		return nil
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	for i := len(cmds) - 1; i >= 0; i-- {
+		d, err := cmds[i].(*redis.DurationCmd).Result()
+		if err != nil {
+			return nil, err
+		}
+		if d != -1 {
+			keys = append(keys[:i], keys[i+1:]...)
+		}
+	}
+
+	return keys, nil
+}
+
+func del(ctx context.Context, rdb *redis.Client, in <-chan string) error {
+	pipe := rdb.Pipeline()
+
+	for key := range in {
+		pipe.Del(ctx, key)
+
+		if pipe.Len() < 100 {
+			continue
+		}
+
+		if _, err := pipe.Exec(ctx); err != nil {
+			return err
+		}
+	}
+
+	if _, err := pipe.Exec(ctx); err != nil {
+		return err
+	}
+
+	return nil
+}

example/lua-scripting/README.md

@@ -1,6 +1,6 @@
 # Redis Lua scripting example
 
-This is an example for [Redis Lua scripting #](https://redis.uptrace.dev/guide/lua-scripting.html)
+This is an example for [Redis Lua scripting](https://redis.uptrace.dev/guide/lua-scripting.html)
 article. To run it:
 
 ```shell

pipeline.go

@@ -24,6 +24,7 @@ type pipelineExecer func(context.Context, []Cmder) error
 // depends of your batch size and/or use TxPipeline.
 type Pipeliner interface {
 	StatefulCmdable
+	Len() int
 	Do(ctx context.Context, args ...interface{}) *Cmd
 	Process(ctx context.Context, cmd Cmder) error
 	Close() error
@@ -53,6 +54,15 @@ func (c *Pipeline) init() {
 	c.statefulCmdable = c.Process
 }
 
+// Len returns the number of queued commands.
+func (c *Pipeline) Len() int {
+	c.mu.Lock()
+	ln := len(c.cmds)
+	c.mu.Unlock()
+	return ln
+}
+
+// Do queues the custom command for later execution.
 func (c *Pipeline) Do(ctx context.Context, args ...interface{}) *Cmd {
 	cmd := NewCmd(ctx, args...)
 	_ = c.Process(ctx, cmd)