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simple.go
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simple.go
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// Copyright (c) 2013 Couchbase, Inc.
// Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
// except in compliance with the License. You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
// Unless required by applicable law or agreed to in writing, software distributed under the
// License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
// either express or implied. See the License for the specific language governing permissions
// and limitations under the License.
package simple
import (
"github.com/couchbaselabs/clog"
"github.com/couchbaselabs/tuqtng/optimizer"
"github.com/couchbaselabs/tuqtng/plan"
"github.com/couchbaselabs/tuqtng/query"
)
type SimpleOptimizer struct {
}
func NewSimpleOptimizer() *SimpleOptimizer {
return &SimpleOptimizer{}
}
// simplest possible implementation
// 1. read all plans off plan channel
// 2. return last plan
func (this *SimpleOptimizer) Optimize(planChannel plan.PlanChannel, errChannel query.ErrorChannel) (*plan.Plan, query.Error) {
plans := make([]plan.Plan, 0)
var p plan.Plan
var err query.Error
ok := true
for ok {
select {
case p, ok = <-planChannel:
if ok {
clog.To(optimizer.CHANNEL, "See plan %v", p)
plans = append(plans, p)
}
case err, ok = <-errChannel:
if err != nil {
return nil, err
}
}
}
if len(plans) > 0 {
chosenPlan := plans[len(plans)-1]
clog.To(optimizer.CHANNEL, "Choosing plan %v", chosenPlan)
return &chosenPlan, nil
}
return nil, query.NewError(nil, "No plans produced for optimizer to choose from")
}