func (d *datastore) Query(q dsq.Query) (dsq.Results, error) {
// we can use multiple iterators concurrently. see:
// https://godoc.org/github.com/syndtr/goleveldb/leveldb#DB.NewIterator
// advance the iterator only if the reader reads
//
// run query in own sub-process tied to Results.Process(), so that
// it waits for us to finish AND so that clients can signal to us
// that resources should be reclaimed.
qrb := dsq.NewResultBuilder(q)
qrb.Process.Go(func(worker goprocess.Process) {
d.runQuery(worker, qrb)
})
// go wait on the worker (without signaling close)
go qrb.Process.CloseAfterChildren()
// Now, apply remaining things (filters, order)
qr := qrb.Results()
for _, f := range q.Filters {
qr = dsq.NaiveFilter(qr, f)
}
for _, o := range q.Orders {
qr = dsq.NaiveOrder(qr, o)
}
return qr, nil
}
func (bd *boltDatastore) Query(q query.Query) (query.Results, error) {
qrb := query.NewResultBuilder(q)
qrb.Process.Go(func(worker goprocess.Process) {
bd.db.View(func(tx *bolt.Tx) error {
buck := tx.Bucket(bd.bucketName)
c := buck.Cursor()
var prefix []byte
if qrb.Query.Prefix != "" {
prefix = []byte(qrb.Query.Prefix)
}
cur := 0
sent := 0
for k, v := c.Seek(prefix); k != nil; k, v = c.Next() {
if cur < qrb.Query.Offset {
cur++
continue
}
if qrb.Query.Limit > 0 && sent >= qrb.Query.Limit {
break
}
dk := ds.NewKey(string(k)).String()
e := query.Entry{Key: dk}
if !qrb.Query.KeysOnly {
buf := make([]byte, len(v))
copy(buf, v)
e.Value = buf
}
select {
case qrb.Output <- query.Result{Entry: e}: // we sent it out
sent++
case <-worker.Closing(): // client told us to end early.
break
}
cur++
}
return nil
})
})
// go wait on the worker (without signaling close)
go qrb.Process.CloseAfterChildren()
qr := qrb.Results()
for _, f := range q.Filters {
qr = query.NaiveFilter(qr, f)
}
for _, o := range q.Orders {
qr = query.NaiveOrder(qr, o)
}
return qr, nil
}