Skip to content

Instantly share code, notes, and snippets.

@Preetam
Created January 26, 2018 03:17
Show Gist options
  • Save Preetam/5b7f75e0cdff36898aa0d1fade227726 to your computer and use it in GitHub Desktop.
Save Preetam/5b7f75e0cdff36898aa0d1fade227726 to your computer and use it in GitHub Desktop.
package main
import (
"fmt"
"io/ioutil"
"log"
"os"
"strconv"
"github.com/dgraph-io/badger"
)
func mustParseNum(v []byte) int {
n, err := strconv.ParseInt(string(v), 10, 64)
if err != nil {
log.Fatal(err)
}
return int(n)
}
func getCounts(it *badger.Iterator) (aggregateEvens, aggregateOdds, evens, odds int) {
for it.Rewind(); it.Valid(); it.Next() {
if it.ValidForPrefix([]byte{'_'}) {
v, err := it.Item().Value()
if err != nil {
log.Fatal(err)
}
n := mustParseNum(v)
if string(it.Item().Key()) == "_even" {
aggregateEvens = n
} else {
aggregateOdds = n
}
continue
}
n := mustParseNum(it.Item().Key())
if n%2 == 0 {
evens++
} else {
odds++
}
}
return
}
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("%d", i))
}
// Initialize
txn := db.NewTransaction(true)
// Set keys 0, 2, 4
for i := 0; i <= 4; i += 2 {
err := txn.Set(bkey(i), []byte{})
if err != nil {
log.Fatal(err)
}
}
err = txn.Commit(nil)
if err != nil {
log.Fatal(err)
}
// Now start two concurrent transactions.
txnA := db.NewTransaction(true)
txnB := db.NewTransaction(true)
{
// txnA adds an even number to the set and updates _odd aggregate count
err = txnA.Set(bkey(6), []byte{})
if err != nil {
log.Fatal(err)
}
it := txnA.NewIterator(badger.DefaultIteratorOptions)
_, _, _, odds := getCounts(it)
// Update count
err = txnA.Set([]byte("_odd"), []byte(fmt.Sprintf("%d", odds)))
if err != nil {
log.Fatal(err)
}
}
{
// txnB adds an odd number to the set and updates _even aggregate count
err = txnB.Set(bkey(1), []byte{})
if err != nil {
log.Fatal(err)
}
it := txnB.NewIterator(badger.DefaultIteratorOptions)
_, _, evens, _ := getCounts(it)
// Update count
err = txnB.Set([]byte("_even"), []byte(fmt.Sprintf("%d", evens)))
if err != nil {
log.Fatal(err)
}
}
err = txnA.Commit(nil)
if err != nil {
log.Fatal(err)
}
err = txnB.Commit(nil)
if err != nil {
log.Fatal(err)
}
err = db.View(func(txn *badger.Txn) error {
it := txn.NewIterator(badger.DefaultIteratorOptions)
aggregateEvens, aggregateOdds, evens, odds := getCounts(it)
if aggregateEvens != evens || aggregateOdds != odds {
return fmt.Errorf("Total (evens, odds) = (%d, %d) doesn't match (_even, _odd) = (%d, %d)",
evens, odds, aggregateEvens, aggregateOdds)
}
return nil
})
if err != nil {
log.Fatal(err)
}
}
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment