Badger example with prefix?

awillis · February 26, 2019, 1:10am

I’m looking for an example of how to set and iterate over a data using prefixes. Could someone please point me in the right direction?

mrjn · February 26, 2019, 6:53am

See: GitHub - dgraph-io/badger: Fast key-value DB in Go.

awillis · February 27, 2019, 2:18am

github.com

awillis/sluus/blob/master/processor/queue.go#L123


		if len(q.head.Get(direction)) > 0 {
			iter.Seek(q.head.Get(direction))
		}

		prefixKey := u64ToBytes(direction)

		key := make([]byte, 0, 32)
		key = append(key, prefixKey...)
		table := crc64.MakeTable(crc64.ECMA)

		for msg := range batch.Iter() {

			payload, err := msg.ToBytes()

			if err != nil {
				q.Logger().Error(err)
			}

			timeKey := u64ToBytes(uint64(time.Now().UnixNano()))
			sizeKey := u64ToBytes(uint64(len(payload)))
			crcKey := u64ToBytes(crc64.Checksum(payload, table))

The prefix key used in the example casts a string as a byte array. I’m using binary.LittleEndian.PutUint64 to create byte arrays from uint64 values. I can store the data, but prefix scans don’t return any data. I didn’t want to have to use a string as a prefix key.

mrjn · February 27, 2019, 3:22am

Someone else can probably help you better, but generally speaking, you’d use a BigEndian encoding for Uint64s so they maintain their order when sorted lexicographically.

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Badger example with prefix?

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