[badger] Prefix + reverse lookup

mrjn · March 20, 2018, 7:22pm

You might be going past the search space. See:

github.com/dgraph-io/badger

Seek iterator with Reverse doesn't work

opened 11:42PM - 09 Mar 18 UTC

closed 08:17PM - 12 Mar 18 UTC

brk0v

kind/question

Code: ```go package main import ( "fmt" "io/ioutil" "log" "os" … "github.com/dgraph-io/badger" ) func main() { dir, err := ioutil.TempDir("", "badger") if err != nil { log.Fatal(err) } defer os.RemoveAll(dir) opts := badger.DefaultOptions opts.Dir = dir opts.ValueDir = dir db, err := badger.Open(opts) if err != nil { log.Fatal(err) } defer db.Close() bkey := func(i int) []byte { return []byte(fmt.Sprintf("%09d", i)) } bval := func(i int) []byte { return []byte(fmt.Sprintf("%025d", i)) } txn := db.NewTransaction(true) // Fill in 1000 items n := 1000 for i := 0; i < n; i++ { err := txn.Set(bkey(i), bval(i)) if err != nil { log.Fatal(err) } } err = txn.Commit(nil) if err != nil { log.Fatal(err) } opt := badger.DefaultIteratorOptions opt.PrefetchSize = 10 opt.Reverse = true // Iterate over 1000 items var count int err = db.View(func(txn *badger.Txn) error { it := txn.NewIterator(opt) for it.Seek([]byte("0")); it.ValidForPrefix([]byte("0")); it.Next() { count++ } return nil }) if err != nil { log.Fatal(err) } fmt.Printf("Counted %d elements", count) } ``` This code returns 0 elements in reverse mode and 1000 elements with reverse = false

github.com/dgraph-io/badger

Iterating in reverse Order - Empty Content

opened 11:56PM - 10 Dec 17 UTC

closed 01:33PM - 11 Dec 17 UTC

rebootcode

kind/question

I am trying to Iterate in Reverse Order, but every time, I set `Reverse` to `tru…e`. It gives empty value. Below is code - ``` txn := db.NewTransaction(false) defer txn.Discard() err = db.View(func(txn *badger.Txn) error { DefaultIteratorOptions := badger.DefaultIteratorOptions DefaultIteratorOptions.Reverse = true it = txn.NewIterator(DefaultIteratorOptions) key := strconv.Itoa(t.Year()) + "-" + strconv.Itoa(int(t.Month())) + "-" + strconv.Itoa(int(t.Day())) prefix := []byte(key) for it.Seek(prefix); it.ValidForPrefix(prefix); it.Next() { item := it.Item() k := item.Key() v, err := item.ValueCopy([]byte(k)) if err != nil { ctx.WriteString("Content not available") return err } blogList, err := decodeBlog(v) if err != nil { fmt.Println("Error: decode: " + err.Error()) } buffer.WriteString("My Content First") } }) ```

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[badger] Prefix + reverse lookup

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